Foreign exchange transactions involved in international currency exchange in the world market. For example, buying a book and the dollar exchange rate. Equivalent use this transaction is a unit of other currencies.
Well, this is a simple explanation of foreign exchange. In foreign exchange trading can bring wealth. You just need to take risks, to see if you do.
Forex market is the largest and most liquid planet. There is no actual construction can move into action to testify Exchange. Unlike in New York and Chicago Stock Exchange, the exchange took place in the position of completely virtual world. Banks, government and large corporations trading continuously, all day and night in the open market and other countries to shut down. Foreign exchange, in itself is a series of computer networks and systems.
Money does not have a fixed value. Monetary value of each country's rapidly changing, and many times during the day and evening classes trade. Including foreign exchange value of money can be changed, because there are too many or no reason. Because of this uncertainty, all foreign exchange transactions is based primarily on speculation.
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New York (Dow Jones) - the dollar rose slightly against major currencies on Friday as traders booked profits and squared positions ahead of the week the high-level public policy.
In addition, the contribution to the crowd on Friday, the euro and other high-yielding currencies back part of the day, as the dollar rebounded late in the day. The dollar has been slipping for two weeks over a wide range of currencies stopped falling even lower Thursday U.S. stocks.
"The dollar has become very oversold in recent weeks, there are no U.S. economic data (Friday), which was ideal environment for profit," said Kathy Liene, chief strategist of world currencies trade in New York.
And U.K. Sterling under pressure on Friday on reports that the UK's largest financial controls designed to Lloyds Banking Group PLC, will probably not attract enough capital to leave the United Kingdom Government's plan for property insurance.
Late Friday night in New York, the euro was 1.4699 from $ 1.4737 late Thursday, according to the iron through CQG. Dollar at Y91.44 from Y91.17. Euro at Y134.41 from Y134.38. And U.K. The British pound to $ 1.6232 from $ 1.6440 and the dollar to CHF1.0297 from CHF1.0285.
Forex: Dealing with your losses
One of the most important rules of Forex trading is to keep your losses as small as you possibly can. With small Forex trading losses, you can stick it out longer than those times when the market moves against you, and be well positioned for when the trend turns around. The one proven method to keeping your losses small is to set your maximum loss before you even open a Forex trading position.
The maximum loss is the greatest amount of capital that you are comfortable losing on any one trade. With your maximum loss set as a small percentage of your Forex trading effort, a string of losses won't stop you from trading for any particular amount of time. Unlike the 95% of Forex traders out there who lose money because they haven't begun to use wise money management rules to their Forex trading system, you will be ok with this money management rule.
To use as an example, If I had a Forex trading float of $1000, and I began trading with $100 a trade, it would be reasonable for me to experience three losses in a row. This would reduce my Forex trading capital to $400. It would then be decided that they're going to bet $200 on the next trade because they think they have a higher chance of winning after having lost three times already.
If that trader did bet $100 dollars on the next trade because they thought they were going to win, their capital could be reduced to $250 dollars. The chances of making money now are practically nil because I would need to make 150% on the next trade just to break even. If the maximum loss had been determined, and stuck to, they would not be in this position.
In this case, the reason for failure was because the trader risked too much money, and didn't apply good money management to the play. Remember, the goal here is to keep our losses as small as possible while also making sure that we open a large enough position to capitalize on profits and minimize losses. With your money management rules in place, in your Forex trading system, you will always be able to do this.
Opening A Forex Brokerage Account
Trading forex is similar to the equity market because individuals interested in trading need to open up a trading account. Like the equity market, each forex account and the services it provides differ, so it is important that you find the right one. Below we will talk about some of the factors that should be considered when selecting a forex account.
Leverage
Leverage is basically the ability to control large amounts of capital, using very little of your own capital; the higher the leverage, the higher the level of risk. The amount of leverage on an account differs depending on the account itself, but most use a factor of at least 50:1, with some being as high as 250:1. A leverage factor of 50:1 means that for every dollar you have in your account you control up to $50. For example, if a trader has $1,000 in his or her account, the broker will lend that person $50,000 to trade in the market. This leverage also makes your margin, or the amount you have to have in the account to trade a certain amount, very low. In equities, margin is usually at least 50%, while the leverage of 50:1 is equivalent to 2%.
Leverage is seen as a major benefit of forex trading, as it allows you to make large gains with a small investment. However, leverage can also be an extreme negative if a trade moves against you because your losses also are amplified by the leverage. With this kind of leverage, there is the real possibility that you can lose more than you invested - although most firms have protective stops preventing an account from going negative. For this reason, it is vital that you remember this when opening an account and that when you determine your desired leverage you understand the risks involved.
Commissions and Fees
Another major benefit of forex accounts is that trading within them is done on a commission-free basis. This is unlike equity accounts, in which you pay the broker a fee for each trade. The reason for this is that you are dealing directly with market makers and do not have to go through other parties like brokers.
This may sound too good to be true, but rest assured that market makers are still making money each time you trade. Remember the bid and ask from the previous section? Each time a trade is made, it is the market makers that capture the spread between these two. Therefore, if the bid/ask for a foreign currency is 1.5200/50, the market maker captures the difference (50 basis points).
If you are planning on opening a forex account, it is important to know that each firm has different spreads on foreign currency pairs traded through them. While they will often differ by only a few pips (0.0001), this can be meaningful if you trade a lot over time. So when opening an account make sure to find out the pip spread that it has on foreign currency pairs you are looking to trade.
How to Trade Forex
Now that you know some important factors to be aware of when opening a forex account, we will take a look at what exactly you can trade within that account. The two main ways to trade in the foreign currency market is the simple buying and selling of currency pairs, where you go long one currency and short another. The second way is through the purchasing of derivatives that track the movements of a specific currency pair. Both of these techniques are highly similar to techniques in the equities market.The most common way is to simply buy and sell currency pairs, much in the same way most individuals buy and sell stocks. In this case, you are hoping the value of the pair itself changes in a favorable manner. If you go long a currency pair, you are hoping that the value of the pair increases. For example, let's say that you took a long position in the USD/CAD pair - you will make money if the value of this pair goes up, and lose money if it falls. This pair rises when the U.S. dollar increases in value against the Canadian dollar, so it is a bet on the U.S. dollar.
The other option is to use derivative products, such as options and futures, to profit from changes in the value of currencies. If you buy an option on a currency pair, you are gaining the right to purchase a currency pair at a set rate before a set point in time. A futures contract, on the other hand, creates the obligation to buy the currency at a set point in time. Both of these trading techniques are usually only used by more advanced traders, but it is important to at least be familiar with them. (For more on this, try Getting Started in Forex Options and our tutorials, Option Spread Strategies and Options Basics Tutorial.)
Types of Orders
A trader looking to open a new position will likely use either a market order or a limit order. The incorporation of these order types remains the same as when they are used in the equity markets. A market order gives a forex trader the ability to obtain the currency at whatever exchange rate it is currently trading at in the market, while a limit order allows the trader to specify a certain entry price. (For a brief refresher of these orders, see The Basics of Order Entry.)
Forex traders who already hold an open position may want to consider using a take-profit order to lock in a profit. Say, for example, that a trader is confident that the GBP/USD rate will reach 1.7800, but is not as sure that the rate could climb any higher. A trader could use a take-profit order, which would automatically close his or her position when the rate reaches 1.7800, locking in their profits.
Forex and Go (Part 2)
Like with the other two PDFT strategies we saw earlier (Forex Cash Cow and Forex Runner) I will teach you step by step how to identify and place a high probability Forex Flip & Go trade. And again, as with all my strategies , Forex Flip & Go is 100% mechanical! You will not use any type of judgment or discretion in your trading. You will only learn to follow simple rules: if A = B do C!
All the strategies you will learn in Forex Trading Methods have incredible benefits that simply make them unique, the best of the best. Forex Flip & Go is no different: One of the only daytrading strategies that is capable of catching a large part of those 80-100 pip EUR/USD daily moves! Rules are 100% mechanical. You will not use any type of judgment or discretion, all your trades will be placed according to simple objective rules. This is a very important aspect of all my strategies and is one of the reasons why Forex Trading Machine traders are so successful. Large profit objectives and VERY small stop losses. This is key. As a daytrader you want to always limit your risk but at the same time you want to ride your winners and squeeze out the last available pip!
Forex Flip & Go allows you to do exactly that. In fact, in order to accomplish this objective I created a mechanism that I have not seen in any other forex daytrading strategy. You will be amazed how this small "trick" keeps you out of bad trades BEFORE you even know you are in a bad trade! Completely disclosed rules. Stop using those trading services or so called "black box" systems. Be in control of your trading. So simple to learn that a 15 year old can trade Forex Flip & Go! No indicators, no vague patterns, no pivots, nothing! Since this is a PDFT strategy you will only use the price of the currency to identify, enter and exit trades. No sitting in front of the computer all day long. Most days you will not trade more than 3 hours. Some days much less. Once 90% of traders realize the market started moving to a certain direction you will already be in the move and profiting from it. Profit objective is pre-set. This means you do not have to think and speculate where to place it. Once you enter the trade you will simply enter a "take profit" order and forget about it.
While most traders will struggle in choppy market days (and of course, lose money in the process!) Forex Flip & Go will keep you out. And much more...
Forex and Go (Part 1)
You already know that the forex market is a 24 hour market. But did you know that every currency pair has it's own special behavior (sort of "personality"!) throughout this 24 hour period? Well, professional traders sure know this and they exploit this characteristic of the forex market to pull in incredible profits day after day.
Now, with Forex Flip & Go (another of my PDFT day trading strategies), you can take advantage of a certain EXPLOSIVE characteristic of the EUR/USD pair (the most liquid of all currency pairs) which produces HIGH PROBABILITY/LOW RISK trades over and over again.
The EUR/USD's daily range is about 80-100 pips ($800-$1,000). As daytraders we want to catch a big portion of this daily move and we want to do it with as little risk as possible. Here is where this beautiful strategy comes to our help! The strength of the Forex Flip & Go strategy is that it catches a large part of these $1,000 swings right at the beginning of the move.Let's look at some examples so you can see exactly what I mean when I say that Forex Flip & Go catches large swings at the very beginning of the move and impressively limits risk:NOTE: Trade examples open in a new window.
Many of the best performing professional traders agree that the key to make serious money in daytrading is having small losses and large gains. That is exactly what Forex Flip & Go does, it identifies a large move at the beginning BUT if it is wrong it will get you out of the market with a minimal loss. I hope you had the chance to view the example charts I put above, they show exactly how Forex Flip & Go does an amazing job of exiting the market when it is wrong (with losses many times smaller than 10 pips!) and how it exploits large moves from beginning to end.If you are serious about being a successful forex daytrader and learning one of the best methods to consistently capture profitable trades then Forex Flip & Go is for you!
Forex Cash Cow Strategy
Forex Cash Cow strategy is truly amazing. I consider it by far my best PDFT swing trading strategy. This incredible system is 100% mechanical, this means it requires ABSOLUTELY NO discretion, interpretention, or judgment. You will simply learn to follow strict rules: if A = B then do C!Since it is a PDFT strategy you will not use ANY type of indicators, the only thing you will need to know is the price of the currency pair you are trading.It truly takes 1 minute per week to implement this strategy, making it perfect for people who do not have the necessary time to monitor the market. In fact, I constantly get emails from Forex Cash Cow traders who say they are making more money trading this system than at their current day jobs!Let's look at how easy it is to trade the Forex Cash Cow strategy:
STEP 1 : Every day after the end of the trading day the trader checks to see if condition one of the system has been met. No interpretation or judgment, it is either yes or no, black or white! This step takes exactly 10 seconds. If condition one has not been met, nothing happens. If met it means there could be an entry signal the next trading day (the trader already knows to what direction, long or short) and step 2 comes into play.
STEP 2 : The next day the trader simply enters three types of orders with his or her broker: a limit order for initiating the trade, a stop loss order to limit risk and a profit objective. All these three numbers are exact pre-set numbers that you will learn how to calculate in less then 10 seconds. Again, no interpretation or judgment, just follow exact rules.
STEP 3 : Wait for results!As traders say, a chart is worth 1000 words! Let's look at several examples of Forex Cash Cow trades. Simply click on the below chart images, chart will open in new window
Forex Trading Methods!
One of the true strength of Forex Cash Cow (and of the other 2 systems I teach in my course) is the fact that it is 100% mechanical. Traders who have been around for some time know the incredible benefits a mechanical system has over non-mechanical trading strategies.
Let's look at some of the amazing benefits of the Forex Cash Cow strategy: No interpretation or judgment required. Since this is a 100% mechanical trading strategy you will be trading completely stress free. This is key with ANY trading strategy. Human emotions is what ultimately breaks traders. With Forex Cash Cow you are guaranteed to not have this problem.Easy to follow rules. As simple as if A = B do C!Works the same for everyone who follow the exact rules (unlike non-mechanical trading methods that work for the very few, and most of the time not even that) Impressively easy to learn. Most Forex Cash Cow traders can put this amazing strategy to work the next day after learning it.
Know today if tomorrow there will be a trade. Yes! You will know a day ahead if a trade is going to be triggered or not.
No monitoring the market. Many people want to trade the forex market but simply don't have the necessary time. Now, with Forex Cash Cow you can trade even if you have a day job! It simply takes 1 minute per week to implement it.
The forex market is known for it's large price swings that when properly traded result in amazing profits. Forex Cash Cow not only trades these price swings with great success BUT it identifies only the best of the best swings, the top percent.No more buying "black box" systems or subscribing to signal providers. All the strategies rules are 100% disclosed and explained. You will have complete control over your trading.
A unique PDFT (Price Driven Forex Trading) strategy. No indicators, no vague chart patterns, no pivots, no support and resistance, no anything you have seen or read until now.And much more....!
Forex Runner
Learn how to day trade the forex market and consistently nail $200, $300 or $400 trades over and over again. Forex Runner is simply one of the best day trading systems I have ever traded. And, being one of my unique PDFT strategies, you will not use any tools or indicators to trade it, the ONLY thing you will need is the price of the currency pair.Forex Runner let's you trade 100% emotion-free since it is completely mechanical. It's rules are incredibly easy to understand, it will not take you more than one hour to learn how to trade it.
One of the amazing characteristics of Forex Runner is that it let's you trade when ever you have time. Since the forex market is a 24 hour market, you have the luxury to decide exactly when it is best for you to put Forex Runner to work.
If you have been around for some time in the trading business you know how hard it is to find a consistently profitable day trading strategy. Forex Runner was built to be consistent. Small stop losses, large profit objectives and a large percentage of winning trades makes Forex Runner one of the top performing forex trading systems.Here are some of the many benefits Forex Runner traders have:A revolutionary Price Driven Forex Trading (PDFT) strategy.
You will not use any type of indicators, identify any vague patterns, or use support or resistance levels etc. You will only use the price of the currency pair to identify, enter and profit from the trade.You will learn how to exploit the daily range of the major currency pairs.How to enter "hit and run" trades; i.e. Identify fast, enter fast and profit fast!Fully disclosed system: no need to buy, rent or subscribe to any service. You control your trading, you decide when to trade, you decide how much to trade.
So easy to learn that most of my traders (many who are completely new to forex trading) put Forex Runner to work only 1 day after learning it.
No stress, no emotions: Since Forex Runner is 100% mechanical you will only follow strict rules to identify, enter and exit trades. No interpretation or judgment what so ever (if you trade already, you most likely know the value of 100% mechanical trading)!Cheat most daytradres! While 90% of traders will identify trades only after the market started moving (and trust me, most enter as the move is ending!), you will have already identified and entered trades BEFORE the market started moving.
Be your own boss, chose when to trade. Since the forex market is active 24 hours a day, no matter what part of the world you live in you can put Forex Runner to work for you!Profit objective is pre-set. This means you do not have to think and speculate where to place it. Once you enter the trade you will simply enter a "take profit" order and forget about it.
Factors affecting Forex trade
The value of a country's currency is influenced by a number of factors: The economics of the country, its trade deficit, political and social environment.
If the current government's deficit increases, its currency's value will fall. As the government decreases its deficit, the currency can begin to recover value and the exchange rate will become more favorable. The same relationship holds true with a country's trade deficit. If the country imports more goods and services than it exports it will have a negative influence on the currency.
Inflation lessens the ability of a unit of currency to buy less and less, so the currency loses value. If the inflation becomes rampant the currency is valued less because it's also viewed as unstable. As the rate of inflation begins to decline the currency begins to increase in value.
Politics and social changes can play havoc with the currency exchange rates. Changes in the regime that are viewed negatively can lower the value of the country's currency in the short term and continue into the long term. If the present government makes decisions that are looked at negatively it can decrease the currency value as well. The opposite can happen. Current government officials can make policy changes that are viewed positively by the rest of the world and that can increase the value of the currency.
For the United States, interest rates and the price of oil can have a major impact on the value of the US dollar.
Interest rates effect how much it's going to cost to borrow money and how much can be earned on investments. Historically if the US raises its interest rates it attracts foreign investors. Those investors have to sell their own currency in order to buy U.S. dollars to purchase treasury bonds. If the interest begins to drop, or the perception is that the rates won't rise any more, investors may purchase Euros as an alternative investment which lowers the value of the US dollar.
The United States is dependent on foreign oil production. Many US industries are dependent on oil and an increase in the price of oil means an increase in their expenses and a drop in profits. In a similar way, a country's dependency on oil influences how the country's currency is valued and will be impacted by changes in oil prices. The US's dependency on oil makes the dollar more sensitive to oil prices than countries who aren't so dependent. As the price of oil increases the value of the dollar drops.
World events and wise Forex trading
Forex trading has the great potential of becoming a profitable and fulfilling career that will let you have a lifestyle that few other lucrative activities in the world can offer to people from many roads in life and without asking any of those men and women for a diploma or some special certification.
But Forex trading is not easy; it may be simple to enter and place your first trade but becoming a profitable trader is a different thing. You will need to acquire the right knowledge and techniques in order to understand and know when to enter or leave a trade always fulfilling the main objective every trader must have; making money.
There are two kinds of analysis you can perform on the Forex markets. They are known as technical analysis and fundamental analysis. It is common that traders tend to divide themselves into "technical" and "fundamentalists". Each group devoting themselves to the main tools each kind of analysis gives them.
Technical forex traders base their trading on the analysis of the charts and the number of indicators derived from the plots of price oscillations and patterns. Meanwhile Fundamentalists traders base their trading mostly on the fundamental numbers and economical indicators of countries economies. Though, even if divided, both tendencies tend to complement each other to some degree.
In this article I will place myself on the "fundamentalists" side and focus on one of the situations every forex trader must be aware of and don't let the events involved affect his trading efforts.
This risky situation is that when unprecedented chaotic world events start to develop as the trading day goes on. The power of the media (tv, internet, printed) can magnify and sometimes it may even distort the events taking place and impacting the trading journey in a significant manner. The result of this magnification and rapid diffusion of the news about the series of unfavorable events taking place is an increased atmosphere of fear, confusion and uncertainty in the trading world. And fearful traders are not prone to make the best trading choices because they have given themselves to panic and emotional reactions instead of reasoned and intelligent decisions.
If you need to have more specific examples of these kind of events you can search a bit inside your memories and consider the impact of just a few types of unfavorable chaotic world events as the political upheavals or corporate scandals of companies as; Enron, WorldCom, or of people as the case of Martha Stewart trial, etc. There is also the example of the terrorist attacks on Sep 11 in New York, March 11 in Spain, etc. Also natural disasters: tsunamis, earthquakes, floods, freezes, droughts, hurricanes along with wars can cause great disruption in a trading journey.
In short, every forex trader should be totally sure that his method of trading has built-in safe guards (stops, limit orders) to prevent a major financial loss from his trading account in case any of the unfavorable events I mentioned above ever takes place. And being realistic, many of those events will surely happen in the future.
Online Forex Trading
Do you know what Forex trading is? Some people have heard of this type of trading, others have not. If you haven't, it might be something you are interested in trying. Forex trading stands for foreign exchange trading. What it consists of is the buying and selling of different currencies. This is done simultaneously, and there are people who make a lot of money with this kind of trading. This is apparent by the 1.9 million dollar turnover in this market that happens every day. Also a lot of it is done online. Online Forex trading is very popular.
The most common currencies to trade are the Euro and the U.S. dollar, and the U.S. dollar and the Japanese Yen. However, nearly all of the Forex trading done involves the major currencies of the world. These include the Euro, Japanese Yen, U.S. dollar, Canadian dollar, British Pound, Australian dollar, and the Swiss franc. The Forex exchange is different from other exchanges, such as the New York Stock Exchange, in that it does not have a physical location or central exchange. The exchange day begins in Sydney, then moves to Tokyo, on to London, and finally ends in New York. Each country takes the responsibility of regulating the Forex exchange activities in their own country. So there is no overall regulatory agency. However, this does not seem to be a problem and most countries do very well at overseeing Forex exchange activities.
There are a lot of things that influence the Forex rate. For instance, economic things, like interest rates and inflation, and also political things, such as political unrest in other countries and major changes in government cause up and down changes in the Forex rate. However, these things tend to be short-term, and don't affect it for long.
Online Forex trading sites are easy to find by surfing the Internet. Most of them provide a wealth of information for the first time trader. You can find out about the history of Forex trading, how to co it, tips on being successful, etc. You can also start trading with as little as $250 in your account on some sites. For anyone who is interested in currency or trading, it is something you should check out.
As with any type of trading, there are no guarantees that you will make money or that you won't make money. It is a smart choice to learn as much as you can about online Forex trading before investing any money and doing any trading. It is a fact that informed investors do better than those who don't know much about what they are trading. So get the fact before you dive in. You might just make a little money in a very interesting currency exchange.
Advantages of the Forex Market
What are the advantages of the Forex Market over other types of investments?
When thinking about various investments, there is one investment vehicle that comes to mind. The Forex or Foreign Currency Market has many advantages over other types of investments. The Forex market is open 24 hrs a day, unlike the regular stock markets. Most investments require a substantial amount of capital before you can take advantage of an investment opportunity. To trade Forex, you only need a small amount of capital. Anyone can enter the market with as little as $300 USD to trade a "mini account", which allows you to trade lots of 10,000 units. One lot of 10,000 units of currency is equal to 1 contract. Each "pip" or move up or down in the currency pair is worth a $1 gain or loss, depending on which side of the market you are on. A standard account gives you control over 100,000 units of currency and a pip is worth $10.
The Forex market is also very liquid. When trading Forex you have full control of your capital.
Many other types of investments require holding your money up for long periods of time. This is a disadvantage because if you need to use the capital it can be difficult to access to it without taking a huge loss. Also, with a small amount of money, you can control
Forex traders can be profitable in bullish or bearish market conditions. Stock market traders need stock prices to rise in order to take a profit. Forex traders can make a profit during up trends and downtrends. Forex Trading can be risky, but with having the ability to have a good system to follow, good money management skills, and possessing self discipline, Forex trading can be a relatively low risk investment.
The Forex market can be traded anytime, anywhere. As long as you have access to a computer, you have the ability to trade the Forex market. An important thing to remember is before jumping into trading currencies, is it wise to practice with "paper money", or "fake money." Most brokers have demo accounts where you can download their trading station and practice real time with fake money. While this is no guarantee of your performance with real money, practicing can give you a huge advantage to become better prepared when you trade with your real, hard earned money. There are also many Forex courses on the internet, just be careful when choosing which ones to purchase.
Forex: Dealing with your losses
One of the most important rules of Forex trading is to keep your losses as small as you possibly can. With small Forex trading losses, you can stick it out longer than those times when the market moves against you, and be well positioned for when the trend turns around. The one proven method to keeping your losses small is to set your maximum loss before you even open a Forex trading position.
The maximum loss is the greatest amount of capital that you are comfortable losing on any one trade. With your maximum loss set as a small percentage of your Forex trading effort, a string of losses won't stop you from trading for any particular amount of time. Unlike the 95% of Forex traders out there who lose money because they haven't begun to use wise money management rules to their Forex trading system, you will be ok with this money management rule.
To use as an example, If I had a Forex trading float of $1000, and I began trading with $100 a trade, it would be reasonable for me to experience three losses in a row. This would reduce my Forex trading capital to $400. It would then be decided that they're going to bet $200 on the next trade because they think they have a higher chance of winning after having lost three times already.
If that trader did bet $100 dollars on the next trade because they thought they were going to win, their capital could be reduced to $250 dollars. The chances of making money now are practically nil because I would need to make 150% on the next trade just to break even. If the maximum loss had been determined, and stuck to, they would not be in this position.
In this case, the reason for failure was because the trader risked too much money, and didn't apply good money management to the play. Remember, the goal here is to keep our losses as small as possible while also making sure that we open a large enough position to capitalize on profits and minimize losses. With your money management rules in place, in your Forex trading system, you will always be able to do this.
Doppler Shift
Precise measurement of the velocity or change of position of stars tells us the extent of the star's movement induced by a planet's gravitational tug. From that information, scientists can deduce the planet's mass and orbit.
Why does a planet cause a star to sway? If a star has a single companion, both move in nearly circular orbits around their common center of mass. Even if one body is much smaller, the laws of physics dictate that both will orbit the center of the combined star and planet system. The center of mass is the point at which the two bodies balance each other.
The radial velocity method measures slight changes in a star's velocity as the star and the planet move about their common center of mass. In this case, however, the motion
detected is toward the observer and away from the observer. Astronomers can detect these variances by analyzing the spectrum of starlight. In an effect known as Doppler shift, light waves from a star moving toward us are shifted toward the blue end of the spectrum. If the star is moving away, the light waves shift toward the red end of the spectrum.
This happens because the waves become compressed when the star is approaching the observer and spread out when the star is receding. The effect is similar to the change in pitch we hear in a train's whistle as it approaches and passes.
The larger the planet and the closer it is to the host star, the faster the star moves about the center of mass, causing a larger color shift in the spectrum of starlight. That's why many of the first planets discovered are Jupiter-class (300 times as massive as Earth), with orbits very close to their parent stars.
Astrometric Measurement
As with the radial velocity technique, this methods depends on the slight motion of the star caused by the orbiting planet. In this case, however, astronomers are searching for the tiny displacements of the stars on the sky.
The planets of our solar system have this effect on the Sun, producing a to-and-fro motion that could be detected by an observer positioned several light years away.
An important goal of the Space Interferometry Mission is to detect the presence of Earth-size planets orbiting nearby solar type stars via narrow angle astrometry. Similarly, the Keck Interferometry will conduct an astrometric survey of hundreds of stars to search for planets with masses as small as UranuTransit Method
If a planet passes directly between a star and an observer's line of sight, it blocks out a tiny portion of the star's light, thus reducing its apparent brightness.
Sensitive instruments can detect this periodic dip in brightness. From the period and depth of the transits, the orbit and size of the planetary companions can be calculated. Smaller planets will produce a smaller effect, and vice-versa. A terrestrial planet in an Earth-like orbit, for example, would produce a minute dip in stellar brightness that would last just a few hoursGravitational Microlensing
This method derives from one of the insights of Einstein's theory of general relativity: gravity bends space. We normally think of light as traveling in a straight line, but light rays become bent when passing through space that is warped by the presence of a massive object such as a star. This effect has been proven by observations of the Sun's gravitational effect on starlight.
When a planet happens to pass in front of a star along our line of sight, the planet's gravity will behave like a lens. This focuses the light rays and causes a temporary sharp increase in brightness and change of the apparent position of the star
Astronomers can use the gravitational microlensing effect to find objects that emit no light or are otherwise undetectable.
Science - Finding Planets
Since planets do not give off their own light, observing them directly presents formidable challenges. Missions such as Terrestrial Planet Finder will rely on advanced technologies that can harness special properties of light to extend our vision. For a more detailed discussion of planet imaging
Science - Finding Planets
Since planets do not give off their own light, observing them directly presents formidable challenges. Missions such as Terrestrial Planet Finder will rely on advanced technologies that can harness special properties of light to extend our vi
How to Take Snapshots of Distant Worlds
One of the grand challenges of NASA's search for new worlds is to develop technologies that will allow us to obtain the first images of planets circling distant stars.
While the parent star is the source of light that will make any planet visible, its glare is between a million and 10 billion times brighter than the faint little speck we are looking for. Therefore, any detailed study of extrasolar planets will require methods to cover up or otherwise control the glare of the parent star so that we can study its immediate surroundings.
Another challenge stems from the fact that, compared to the separation between most things in the universe, planets are located extremely close to their parent stars. For this reason, we need very high resolution to separate the planet from its nearby host.
The following is an overview of several techniques in development that could overcome these obstacles and make extrasolar planet imaging a reality.
Coronagraphs
Originally invented to study the Sun, a coronagraph is a telescope designed to block light coming from the solar disk, in order to see the extremely faint emission from the region around the Sun, called the corona. It was invented in 1930 by B. Lyot to study the Sun's corona at times other than during a solar eclipse. The coronagraph, at its simplest, is an occulting disk in the focal plane of a telescope or out in front of the entrance aperture that blocks out the image of the solar disk, and various other features to reduce stray light so that the corona surrounding the occulting disk can be studied.
However, this technology is now being refined and adapted for the purpose of studying the region around distant stars in search of planets themselves or spectral evidence of planets. One challenge with this approach lies in the diffraction of light around the edges of the occulting shape, which detracts greatly from the potential angular resolution of the image.
The diffraction pattern of a simple round telescope, for example, is a series of concentric rings with a bright central spot. Blocking the light from a star in order to see an orbiting planet requires suppressing the first several bright rings without blocking out the planet. By using a different shape, the diffraction pattern can be controlled so that the starlight is much dimmer closer to the center in some areas, and brighter in others. The telescope can be rotated about its line-of-sight so that the planet image passes in an out of the regions where the starlight is dim.
Managing this diffraction pattern isn't too difficult -- there are a number of options available to accomplish this. So, the technologies under study include various tricks to block out as much of the starlight as possible, while managing the diffraction pattern such that the planet can be seen peeping out from beyond the diffraction bands.
Other proposed solutions for dealing with scattered light within the telescope include novel-shaped apertures, odd-shaped pupils, pupil masks to suppress some of the diffraction, and deformable mirrors.
To appreciate the difficulty the phenomenon of diffraction presents to the development of a coronagraph technology for studying other solar systems, see A closer look at diffraction .
Another possibility is to combine techniques of coronagraphy with interferometry. A coronagraph could also incorporate a spectrometer, so that chemical signs of life could be sought within the light reflected from a planet.
Interferometers and Nulling
An alternative way to get a picture of a distant planet is to replace one large mirror with a number of smaller mirrors and combining their light in a process called interferometry.
Using optical interferometers to study distant planets would allow for smaller mirrors, which can obtain a resolution equal to a single telescope as big as the largest separation between the individual telescopes.
To get enough of this information to build up a good picture, the interferometer must rotate around to different relative positions and repeat the "exposures." As well as taking a picture, an interferometer can obtain spectra of the targets it is looking at.
Interferometers provide extremely good angular resolution. That means they are very good at sorting out which light waves come from which part of the star system. Additionally, an interferometer can be "tuned" so that the light coming from the exact center in the field of view (where the star is) will be blanked out or nulled, while the light from any other area will be viewed normally.
The form of Universal Gravitation
The first thing to note is that the force of gravity must be independent of the type of material since all objects fall with the same acceleration, g. Therefore, the gravitational force must depend on mass alone. The dependence appears to be linear since Fgrav. = mg for an object of mass m. Consider two point masses, m1 and m2, as shown below.
The force acting on m1 should be F12 = m1k1, where k1 depends, at the very least, on the distance between the point masses. We have already established that k1 must be proportional to 1/r122, the distance between the point masses and that the force should be directed along a line connecting the two and pointing toward m2 (the latter comes from the fact that we assumed that the force of attraction for a circular orbit was a central one, i.e. the force connects the centers-of-mass). By the same reasoning, the force acting on m2 should be F21 = m2k2. But, by Newton's Third Law, we must have F21 = F12 and oppositely directed along the line between the point masses and pointing toward m1. The simplest consistent mathematical form is to have
k1 = Gm2/r 122
k2 = Gm1/r 122
where G is the universal constant of gravitation and must have units of Nt*m2/kg2. Therefore, Newton asserted that the gravitational force between two point masses is proportional to the product of the masses and inversely proportional to the square of the distance between the masses.
Introduction of The Solar System
Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system.
The Sun's nearest known stellar neighbor is a red dwarf star called Proxima Centauri, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space. The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun's north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides.
Does life exist on other planets beyond our Solarsystem
Does life exist on other planets beyond our Solarsystem? There is a high probability that life does exist on other planets than Earth.
But what do mean by 'life'? When we're talking about life we mean life as we know it: carbon based organic life forms that needs liquid water to exist.
So not all planets are capable of sustaining life. We know that already for quite some time, because in our Solarsytem Earth is the only planet of which we certain know that it sustains life. Mars could also have had life on it, but that isn't for sure. A planet has to meet certain conditions to be able to support life; the main condition is that the planet has to lie in the habitable zone. This is the region around a star in which life-supporting planets can exist; the boundaries are named the inner and outer edge of the habitable zone.
This means the habitable zone of a star requires certain conditions for a planet:
the star has to be a main sequence star (i.e. a star burning steadily light elements into heavy ones) the planet has to be solid to allow for a liquid-solid interface, this to enhance the exchange between molecules the planet has to be at the right distance from the star to allow for liquid water (temperature dependence) With the formula below (J. Schneider)¹ we can calculate the equilibrium temperature of a planet orbiting a certain star. A planet acquires, by heating, an equilibrium temperature Tp given by: ,Where A is the mean albedo (reflectance) of the planet surface at a distance a around a star with radius Rs and temperature Ts. On this page I will outline some things related to the question on top of this page.
The habitable zone (HZ) is the region around a star in which life-supporting planets can exist (Huang 1959,1960).
The habitable zone for Earth-like planets orbiting main sequence stars, is determined by water loss on the inner edge and by CO2 condensation, leading to runaway glaciation, on the outer edge. Planetary habitability is critically dependent on atmospheric CO2 and its control by the carbonate-silicate cycle. Conservative estimates for the boundaries of the Sun's (G type star) current HZ are 0.95 AU for the inner edge and 1.37 AU for the outer edge. The actual HZ width is probably greater, but is difficult to determine an exact value because of uncertainties regarding clouds which affect the planetary albedo. HZ widths around other stars in the spectral classification range of interest, F to M (~7200 to ~3000 Kelvin), are approximately the same if distances are expressed on a logarithmic scale (i.e. if you plot the distances from the inner and outer edges of the CHZs for different stars on a logarithmic axis, you will find that the widths of the CHZs for the different stars is about the same on this scale). If planets exist around other stars (they do) and if planetary spacing is logarithmic, as in our Solar System, the chances that one or more planets will be found within a star's HZ are fairly good.
The continuously habitable zone (CHZ) is the HZ that stays the HZ during the lifetime of the star. Because the star evolves the boundaries of the HZ will change slightly too, the CHZ will not change so the width of the CHZ will be smaller than the width of the HZ.
The width of the continuously habitable zone (CHZ) around a star depends on the time that a planet is required to remain habitable and on whether a planet that is initially frozen can be cold-started by a modest increase in stellar luminosity. CHZs are generally narrower than HZs because the boundaries of the CHZ migrate outward as a star ages. Despite this, the 4.6 Gyr CHZ around our own Sun extends from at least 0.95 to 1.15 AU and is probably considerably wider. CHZs around early K stars should be somewhat wider (in log distance) than around G stars because the K stars evolve more slowly. Equivalently, one could say that their CHZs are longer-lived. Since there are approximately three times as many K stars as G stars, this suggests that the majority of habitable planets may reside around K stars. Late K stars and M stars would have even wider CHZs, but the planets within them are susceptible to tidal damping and will probably rotate synchronously after a few billion years. F stars should have narrower CHZs than do G stars (on a log distance scale) because they evolve more rapidly. High ultraviolet flux are another potential problem for life around F stars. Stars earlier than ~F0 have main sequence lifetimes of less than 2 Gyr, so their planets are probably not suitable for evolving intelligent life. But 'simple life' could evolve here.
Discovered planets
Most extra-solar planets that have been discovered have been found by using Doppler technique. I've listed a table and a schematic diagram of the recently discovered planets around main sequence stars. I've also made a table with some data on Jupiter and Earth. These are planets who are the most likely to support life. As you can see most planets have small orbital values, and the mass is also quite big. Solid planets most have masses of ~15 Earthmasses, planets with higher mass are mostly of the gaseous type. This means the surface temperature would be way to high to support life, and the planets would all be of the gaseous type. None of them is likely to be solid and none of them is likely to be a candidate for a life sustaining planet.
There have also been planets found orbiting pulsars. A pulsars is a radio source that emits signals in very short, regular bursts; it's a highly magnetic, rotating star of extremely high density and small size that is composed mainly of very tightly neutrons (neutron star, mass no bigger than ~3 solar masses). We expect here more extreme conditions, and a habitable zone is not very likely. The object orbiting these pulsars are most Earth like masses and solid, but there have also Jupiter like masses been found; data can be found at Darwin Project and Extra-solar Planets Catalog.
Objects with mass > 13 Jupiter masses are commonly named Brown Dwarfs. This is a very low mass objects (~0.01-0.08 solar mass) of low temperature and luminosity that never becomes hot enough in its core to ignite thermonuclear reactions. So you can't really call them planets, they are some kind of stars that have failed to become a star. Several of these kind of object have also been found orbiting stars; data can be found at Darwin Project and Extra-solar Planets Catalog.
But why have only these kind of planets been found orbiting main sequence stars? The answer lies in the Doppler technique used to find these planets. These kind of planets are easiest to discern using this observation technique. To discover less massive planets in more high orbit you would need more high-precision Doppler observations, but that isn't conceivable yet. You could also use more precise observation techniques like micro-lensing, but micro-lensing events are more rare and there's only one chance to collect the data.
Let's make some assumptions for the quantities in the formula above to estimate the planets surface temperature.
The stars listed in the table are all of the F and G type. This means the temperatures of the stars ranges from ~5100 to ~7200 degrees Kelvin. Use this for Ts. The mean albedo A for earth is 0.39, that of Jupiter is 0.51. Use a value of the same size here also. The radius Rs of typeV G and F stars is about the same as the radius of the sun, 6.96 .10^5 km (range is about 1.3 Rsun (F0V) to 0.85 Rsun (G9V)). The value for a is given in the table below, the radius of the orbit. 1 AU = 1.496 .10^8km The estimated temperatures of the stars and the calculated temperatures of the planets are listed in table 1. One can see as the orbit becomes bigger the temperature drops. Some of the planets have high eccentricity's, this means that the temperature will vary a lot, because of the smaller and greater distance from the star. Since all planets are probably gaseous, you wouldn't expect life to evolve there.
table 1: Some data of planets around main sequence stars (data from Darwin Project and Extra-solar Planets Catalog) :
As you might notice, the mass is given in Jupiter mass·sin i, where i is the inclination of the planet's orbit. Because the orbital inclination cannot be retreived from the observations, the mass range could be quite big. For the temperature estimate is used: Albedo = 0.5, Rs = Rsun (~ 4.74 .10^-3 AU) then Tp = (0.041/a^1/2).Ts, a in AU
Which primary conditions are necessaryfor life as we know it?
Going to extremes
Life can exist in the strangest inhospitable places on earth. It are mostly bacteria or algae that apperently choose extreme lifeconditions.Especially in the deep-seas live so-called "super-thermophilic" (=extremely-heatloving) micro-organisms, these not only exist, but thrive at temperatures even beyond 150 ° C (Baross & Deming, 1993). They inhabit pressurized enviroments beneath deep-sea hydrothermal vents. At this temperatures you might expect the water to boil, but it doesn't because of the immense pressure. Recently bacteria were discovered which live at an astonishing 169 ° C! It's not only the temperature, lots of organisms at places where no sunlight ever comes use chemicals like hydrogen sulfite as their energy source. The bacteria inturn sustain larger organisms in the ventcommunity. Also well into the Earths crust, the toplayer of the earth, microbes are found. The mounting pressure has little direct effect on them even at several kilometres below groundlevel. It is the increasing temperature that limits the depth of life beneath the surface. In the oceanic crust the temperature rises about 15 ° C per kilometre. So microbial life extends on average about 7 kilometres below the sea floor. For continental crust the microscopic life should reach almost 4 kilometres into the earth, for the surface temperature is approximately 20 ° C and it rises with 25 ° C per kilometre. However the amount of micro-organisms will vary from place to place.
BacteriaFrom biology-courses we know that bacteria have an optimum curve, which means that at certain temperatures they have a peak where they thrive most. At too cold temperatures they go into somesort of stasis, you could compare it with hibernation, and they do not show any characteristics of life. If the temperatures increase they become active again. At too hot temperatures, however, they are damaged too severly that the damage is irretrivable.
Conditions necessary for life
If we want to investigate the possibility of life on other planets we have to figure out what exactly we are looking for. You cannot go marching off looking only for planets that resemble Earth as it is nowadays. We shall have to go back to the formation of the Earth and life's origin, things were very different then...
Origin of life
Earth formed about 4.6 billion years ago (= 4.6 Giga years) as third planet in a series of nine circling around a star, the Sun. The Sun and the planets are made from stellardebris of stars that came to the end of their existance. Everything we see around us is actually recycled stardust.After the formation Earth was a pockmarked planet of roughly uniform composition and had an early atmosphere of mainly hydrogen (H2). Then radioactive heating began to melt the interior and the core was formed. Now this heating had as a consequense that degassing from the planets interior created a second atmospere rich in water (H2O), carbon dioxide (CO2), methane (CH4) and Ammonia (NH3). When the surface had cooled enough intense rains began to fall and created the oceans.
It is generaly believed in science that this "prebiotic soup" as it is called is where life originated. The famous Miller-Urey experiment duplicated the conditions of early Earth in a laboratory (Orgel, 1994). In a self-contained apparatus an "atmosphere" consisting of hydrogen, water, methane and ammonia was created above an "ocean" of water. These gasses were subjected to "lightning" in the formof an electrical discharge. They found that 10% of the carbon (C) in the system had converted into organic compounds and 2% of this carbon went on to make amino-acids, the buildingblocks of our carbon-based life.Although doubt has arisen because recent investigations indicate that Earth's early atmosphere may have contained more gasses than in the experiment, like CO2 (Orgel, 1994)(De Jager, 1995). But it is still the best theory we have.These amino-acids that formed on Earth are very important, they are the buildingblocks of the nucleic-acids RNA and DNA which in their turn carry the genetic information of organisms. Whether RNA arose spontanous or replaced some earlier geneticsystem is not quite clear. But its development was probably the key in the development of life. It very likely led to the synthesis of proteins, the formation of DNA and the emergence of a cell that could be the ancestor of all
current lifeforms as theory implies. (Orgel, 1994).
Nowadays one of the vital needs for survival of complex organisms is the presence of oxigen (O2). Yet if one looks at Miller-Urey's experiment one sees that no free oxigen has been included in the initial mixture of gasses. Free oxigen was little or not present at the creation of life on the Earth. For it is an agressive element, it oxidizes other chemicals; it subtracts hydrogen from existing molecules. Therefore under oxidizing conditions amino-acids do not or very little form.The atmosphere plays a major part in the creation of life and sustaining it
Development of life
What has to be said, is that simple models of the evolution of life and its development do not apply. Webs and chains in the past are so intricate and full of random and chaotic events. All scientists have to make assumptions especially on this matter.
As stated before, Earth formed approximately 4.6 billion years ago. It had a to endure heavy bombardments of cosmicdebris. These heavy bombarments ended about 3.8 billion years ago (Kasting, 1993). We know this because the oldest rocks date from that period. The large impacts before this date melted the Earth's surface so no solid rock could exist. Still the oldest rocks to hold cellular fossils date from approximately 3.5 billion years ago(Gould, 1994). Which means that life on Earth evolved quickly and is really old. Those first fossils were of bacteria. Bacteria represent more or less the simplest forms of life, so the only way to expand was in width and height. Or to put it differently, to expand in diversity and in complexity.
After the bacterial cells the cells belonging to the plant- and animal kingdom began to to evolve around 2 billion years ago. Yet, life remained unicellular for the first five sixths of its history. Some of the multicellular algae evolved a bilion yars ago. But no record can be found of multicellular animal organization for the span of 3 bilion years. Even more surprisingly, all major stages organizing animal life's multicellular design occured in a very small timespan. It began less than 600 milion years ago and lasted until 530 million years ago, but the steps are not gradually, they're discontinous. Though it actually took only five million years of intense creativity to develop, called the Cambran explosion,followed by 500 million years of variation.It is not known how nature came up with these anatomical designs so quickly. But this first period of both internal and external flexability gave a range of invertabrate anatomies that may have outnumbered the full range of animal form in all Earth's enviroments today.
The question is why did most of these early experiments die out, while others survived. It's more by luck than by a predictable struggle for existance that those organisms we know survived. For mass extinction mark the boundaries of divisions of geologic-timescale. It is thought that these extinctions were mainly caused by impacts of large extraterrestrial objects which smashed into the Earth (the last of these, about 65 million years ago, is thought to have wiped out the dinosaures). Mass extinctions are not randomly distributed in their inpact on life. Some descendants die and others survive as a practical outcome on presence or absence of evolved characteristics. But if the triggering cause of the extinction is sudden catastrophic, reasons for death or life may lie very close to eachother, they may be random. (Gould, 1994).
What do we call life?
A reasonable biological definition of life: Living systems are capable of: metabolism, growth, reaction to stimuli, reproduction, mutation and reproduction of its mutations.
Necessity of water
It seems that for life on Earth water was and is of the utmost important to us. Earth is clearly distinct from other (terrestrial) planets by its wetness.We will now look at the right distance from a star to allow a planet to have liquid water.We have a planet orbiting at a star. This star has a radius Rs and a temperature Ts. The planet has an albedo (=reflectance) A of its surface. Then its equilibrium temperature will be Tp. The distance between the star and the planet we call a.
Tp = { (1-A) / sqrt2}power 1/4 • (Rs / a)power 1/2 • Ts (1) (J. Schneider, 1995).
If we fill in the values known for Earth we find that A=0.39, Tsun =5770 K, so Tp=280 K (which is very close to the actual 287 K)
So from equation (1) we have a planet having a temperature of approximately 300 ± 20 K to allow for liquid water must be located at a distance from the star given by
a = Rs ( Ts / 300)² (2)
where the albedo is A=1. This distance depends on the type of centralstar. So it ranges from approximately 0.1 Au (1Au is the distance between the Sun and the Earth) for cool stars with Ts = 3000 K to about 2 Au for hot stars with Ts = 6500 K. in the next section we will see that there is more to be dealth with in calculating the habitable distance .
However some assumptions were made in forwarding the two equations we just saw. The one of main interest to us, is that it has we assume to have a solid planet, which would exclude giant gaseous planets like Jupiter. But is this assumption correct? What do we know about Jupiter anyway?
Moreover in 1995 an anouncement was made that large ammount a gassious alcohol had been discovered around a star in its initial formationfase. The temperature of the gas was 125 K, very warm for conditions in interstellarspace. The alcohol and other complicated molecules had probably been formed on dustparticles, when the star got larger and heated the dustparticles, the precipitated gasses evaporated.In meteorites, some even older than the solarsystem itself, complicated organic molecules were found aswell. (De Jager, 1995). It seems that no prebioticsoup was needed to create those. But wether life would be able to originate in anyotherway, without the aid of water remains a mystery.
What's the difference between a star and a planet?
IntroductionIf you want to examine what conditions are necessary for a planet to support live, an important question will be: When do you call an object a planet? Or what is the difference between a star and a planet? In this article I will try to explain the exact difference between the two and I will look at the atmosphere, the mass and the temperature, to examine if live is possible on these objects. Star formationA star forms when a very big cloud of gas contracts under the influence of its own gravitational force. As this contraction takes place the object emits energy. This energy is called fall energy. As a result of this contraction the core gets denser and hotter. When the core reaches a temperature of about 3 million Kelvin, it starts to emit light, because of nuclear fusion ( Krane, K.S) reactions in the core. At this stage the gas cloud will stop its contraction because now the gravitational force is in equilibrium with the pressure build up by the hot gas. When this starts to happen you can say that a new star is born. Planet formationA planet on the other hand is build up out of the dust that surrounds a star. When a star is formed there is still a disk of gas surrounding it. As this gas cools, it condenses and forms solid grains. These grain particles accrete into large bodies called planetesimals, which then collide and accrete to make protoplanets. These protoplanets evolve into planets like the planets in our own solar system. So the formation of a star is totally different from that of a planet. This is the main difference between a star and a planet. If an object has a mass of 0.084 times the mass of our own sun (85 times the mass of Jupiter) the core reaches a point where it can start the process of nuclear fusion in its core (see fig.1). If the mass is smaller than this, the lowest temperature to support nuclear fusion will never be reached and the object will never shine like a star. But can we call all of these objects planets? No, objects with a mass between 85*Mj (85 times the mass of Jupiter) and 13*Mj can't sustain nuclear fusion of elements like hydrogen (H) and helium (He) but can support the fusion of two protons into deuterium (D), early in their lifetime. These objects are called brown dwarfs. They form the transition between stars and planets.
Brown dwarfs
Brown dwarfs form like stars so you can't call them planets, but they have a mass that is to small to sustain the nuclear fusion process that takes place inside a star, so they aren't really stars either. As such an object contracts under the influence of it's own gravity, it doesn't reach the temperature that is needed to start the nuclear fusion from H-nuclei into He-nuclei. But it does reach a high enough temperature for the fusion of protons into deuterium. Because of this fusion it emits light during the first period of it's lifetime. It also emits light because of the fall energy that is produced as a result of the contraction of the gas, but this forms only a minor contribution to the total emission of light. Because very little or no fusion takes place, the core of the star can't build up enough pressure to prevent the star from further contraction under the influence of the gravitational forces that are working on the gas. The gas in the center of the star gets so dense that it degenerates. Now the star won't contract any further because of the pressure that is build up by the degenerated matter. This pressure is called electron degeneracy pressure (EDP) (Kulkarni, S.R.). The origin of this pressure is explained by quantum mechanics as arising from oscillations of confined electrons. Because the fusion and contraction have stopped, the only light emission that is left is due to the cooling of the atoms of the star. During the rest of it's lifetime the star will get dimmer and dimmer and eventually and up as a cool object emitting light in the infrared. The chemical composition of the atmosphere of a brown dwarf strongly depends on it's temperature. But for an atmosphere similar to that of the first detected brown dwarf (gl229B), chemical equilibrium calculations indicate that the upper layers of it's atmosphere mainly exist out of methane (CH4), ammonia (NH3), water (H2O) hydrogen sulfide (H2S) and phosphine (PH3). However deep in the atmosphere methane is "replaced" by carbon monoxide (CO) and ammonia is "replaced" by nitrogen (N2) (Marley, M.S.).
Planets
Planets can be divided into two different groups. The smaller, solid terrestrial planets (like the earth) and the large, liquid Jovian planets (like Jupiter and Saturn). I will concentrate on the jovian planets because the border between brown dwarfs and planets lies in the mass range of these planets. I already explained how planets are formed, but Jupiter and Saturn may have formed in another way. They may have formed like stars. That is they may have formed out of a gas cloud that contracted under the influence of the gravitational force working on it. In this case the only difference between brown dwarfs and jovian planets is the fusion of protons into deuterium in the core of the brown dwarfs. The jovian planets are large gas bulbs with a small massive core, or in the case of bigger planets, the core may exist out of degenerated material. The very thick atmosphere is build up out of several different layers. The principal constituents of the atmospheres of the jovian planets are molecular hydrogen (H2) and helium (He). The outer most layer of the atmosphere (the photosphere), is build up out of a mixture of these gasses. Underneath this layer is a thick layer of liquid hydrogen. Then you get a layer liquid metallic hydrogen and in the center there possibly exists a rocky core. Although most of the atmosphere consists out of hydrogen and helium there are a lot of other molecules in the atmospheres of the jovian planets. As already mentioned, which elements there are, strongly depends on the temperature of the planets. The temperatures of the extra solar planets that have been discovered until now, differ very much from each other, with values ranging from 100-1500 Kelvin. So the chemical composition of the atmospheres are also very different. Figure 3 gives a rough plot of the chemical species that are likely to condense near the photosphere for a given effective temperature. It is most likely that these kinds of planets can't support life because they aren't solid like terrestrial planets, but for more information on this subject you have to visit Saskia's page.
MERCURY
Mercury is the planet closest to the Sun in our Solar System. This small, rocky planet has almost no atmosphere. Mercury has a very elliptical orbit and a huge range in temperature. During the long daytime (which lasts 58.65 Earth days or almost an entire Mercurian year, which is 88 days long), the temperature is hotter than an oven; during the long night (the same length), the temperature is colder than a freezer. Mercury is so close to the Sun that you can only see it near sunrise or sunset.
Craters on the surface of Mercury.
Mercury is a heavily cratered planet; its surface is similar to the surface of our Moon. Cratering on Mercury triggered volcanic eruptions that filled much of the surrounding area. Mercury does have a magnetic field (probably generated by a partly-liquid iron core).
SIZE
Mercury's thin atmosphere consist of trace amounts of hydrogen and helium. The atmospheric pressure is only about 1 x 10-9 millibars; this is a tiny fraction (about 2 trillionths) of the atmospheric pressure on Earth.
Since the atmosphere is so slight, the sky would appear pitch black (except for the sun, stars, and other planets, when visible), even during the day. Also, there is no "greenhouse effect" on Mercury. When the sun sets, the temperature drops very quickly since the atmosphere does not help retain the heat.
Mercury is about 3,031 miles (4,878 km) in diameter. It is the smallest planet in our solar system (it used to be considered the second-smallest planet, when Pluto was still considered to be a planet). Mercury is a bit over one third of the diameter of the Earth. Mercury is only slightly larger than the Earth's moon
MASS AND GRAVITY
Mercury's mass is about 3.3 x 1023 kg. This is about 1/20th of the mass of the Earth.
The gravity on Mercury is 38% of the gravity on Earth. A 100 pound person would weigh only 38 pounds on Mercury. To calculate your weight on Mercury, just multiply your weight by 0.38 (or go the planetary
MERCURY'S ORBIT AND DISTANCE FROM THE SUN
Mercury is closest planet to our Sun and the fastest moving planet in our Solar System. Mercury is just over a third as far from the sun as the Earth is; it is 0.387 A.U. from the sun (on average). Mercury's orbit is very eccentric; at aphelion (the point in the orbit farthest from the sun) Mercury is 70 million km from the sun, at perihelion Mercury is 46 million km from the sun.
There are no seasons on Mercury. Seasons are caused by the tilt of the axis relative to the planet's orbit. Since Mercury's axis is directly perpendicular to its motion (not tilted), it has no seasons.
If you were on the surface of Mercury, the Sun would look almost three times as big as it does from Earth!
TEMPERATURE RANGE
Mercury has a huge range in temperatures. Its surface ranges in temperature from -270°F to 800°F (-168°C to 427°C). During the very long daytime (88 Earth-days long), the temperatures are very high (the second-highest in the Solar System - only Venus is hotter); during the long night, the thin atmosphere lets the heat dissipate, and the temperature drops quickly.
MOONS
Mercury has no moons.
VENUS
Venus is the second planet from the sun in our solar system. It is the hottest planet in our Solar System. This planet is covered with fast-moving sulphuric acid clouds which trap heat from the Sun. Its thick atmosphere is mostly carbon dioxide. Venus has an iron core but only a very weak magnetic field. This is a planet on which a person would asphyxiate in the poisonous atmosphere, be cooked in the extremely high heat, and be crushed by the enormous atmospheric pressure.Venus is also known as the "morning star" or the "evening star" since it is visible and quite bright at either dawn or dusk. It is only visible at dawn or dusk since it is closer to the sun than we are.
Like the moon, Venus' appearance from Earth changes as it orbits around the Sun. It goes from full to gibbous to crescent to new and back.
SIZE
Venus is about 7,521 miles (12,104 km) in diameter. This is about 95% of the diameter of the Earth. Venus is the closest to Earth in size and mass of any of the other planets
MASS AND GRAVITY
Venus' mass is about 4.87 x 1024 kg. The gravity on Venus is 91% of the gravity on Earth. A 100-pound person would weigh 91 pounds on Venus. The density of Venus is 5,240 kg/m3, slightly less dense than the Earth and the third densest planet in our Solar System (after the Earth and Mercury).
LENGTH OF A DAY AND YEAR ON VENUS
Venus rotates VERY slowly. Each day on Venus takes 243 Earth days. A year on Venus takes 224.7 Earth days. It takes 224.7 Earth days for Venus to orbit the sun once. The same side of Venus always faces Earth when the Earth and Venus are closest together.
VENUS' ORBIT AND DISTANCE FROM THE SUN
Venus is 67,230,000 miles (108,200,000 km) from the sun. Venus has an almost circular orbit. On average, Venus is 0.72 AU, 67,230,000 miles = 108,200,000 km from the sun.
Venus rotates in the opposite direction of the Earth (and the other planets, except possibly Uranus). Looking from the north, Venus rotates clockwise, while the other planets rotate counterclockwise. From Venus, the Sun would seem to rise in the west and set in the east (the opposite of Earth). No one knows why Venus has this unusual rotation
TEMPERATURE ON VENUS
Venus is the hottest planet in our Solar System. Its cloud cover traps the heat of the sun (the greenhouse effect), giving Venus temperatures up to 480°C. The mean temperature on Venus is 726 K (452°C = 870°F).
MOONS
Venus has no moons
FIRST SPACECRAFT TO REACH VENUS
Venera 3 (from the U.S.S.R.) was the first manmade object to reach Venus. This Soviet spacecraft was launched on November 16, 1965. On March 1, 1966 , the spacecraft arrived at Venus and the capsule parachuted down to the planet, but contact was lost just before entry into the atmosphere.
VENUS' NAME AND SYMBOL
This is the symbol of the planet Venus. Venus was named after the Roman goddess of love.
EARTH
The Earth is the third planet from the Sun in our Solar System. It is the planet we evolved on and the only planet in our Solar System that is known to support life
SIZE
The Earth is about 7,926 miles (12,756 km) in diameter. The Earth is the fifth-largest planet in our Solar System (after Jupiter, Saturn, Uranus, and Neptune). Eratosthenes (276-194 BC) was a Greek scholar who was the first person to determine the circumference of the Earth. He compared the midsummer's noon shadow in deep wells in Syene (now Aswan on the Nile in Egypt) and Alexandria. He properly assumed that the Sun's rays are virtually parallel (since the Sun is so far away). Knowing the distance between the two locations, he calculated the circumference of the Earth to be 250,000 stadia. Exactly how long a stadia is is unknown, so his accuracy is uncertain, but he was very close. He also accurately measured the tilt of the Earth's axis and the distance to the sun and moon.
THE MOON
The Earth has one moon. The diameter of the moon is about one quarter of the diameter of the Earth.
The moon may have once been a part of the Earth; it may have been broken off the Earth during a catastrophic collision of a huge body with the Earth billions of years ago
MASS, DENSITY, AND ESCAPE VELOCITY
The Earth's mass is about 5.98 x 1024 kg.
The Earth has an average density of 5520 kg/m3 (water has a density of 1027 kg/m3). Earth is the densest planet in our Solar System.
To escape the Earth's gravitational pull, an object must reach a velocity of 24,840 miles per hour (11,180 m/sec).
LENGTH OF A DAY AND YEAR ON EARTH
Each day on Earth takes 23.93 hours (that is, it takes the Earth 23.93 hours to rotate around its axis once - this is a sidereal day). Each year on Earth takes 365.26 Earth days (that is, it takes the Earth 365.26 days to orbit the Sun once).
The Earth's rotation is slowing down very slightly over time, about one second every 10 years.
Orbital Eccentricity
The Earth has an orbit that is close to being circular; its orbital eccentricity is 0.017. (Eccentricity is a measure of how an orbit deviates from circular. A perfectly circular orbit has an eccentricity of zero; an eccentricity between 0 and 1 represents an elliptical orbit.)
THE EARTH'S AXIS TILT AND THE SEASONS
The Earth's axis is tilted from perpendicular to the plane of the ecliptic by 23.45°. This tilting is what gives us the four seasons of the year: Summer, Spring, Winter and Autumn. Since the axis is tilted, different parts of the globe are oriented towards the Sun at different times of the year. This affects the amount of sunlight each receives. For more information on the seasons, click here.
SPEED
At the equator, the Earth's surface moves 40,000 kilometers in 24 hours. That is a speed of about 1040 miles/hr (1670 km/hr). This is calculated by dividing the circumference of the Earth at the equator (about 24,900 miles or 40,070 km) by the number of hours in a day (24). As you move toward either pole, this speed decreases to almost zero (since the circumference at the extreme latitudes approaches zero).
TEMPERATURE ON EARTH
The temperature on Earth ranges from between -127°F to 136°F (-88°C to 58°C; 185 K to 311 K). The coldest recorded temperature was on the continent of Antarctica (Vostok in July, 1983). The hottest recorded temperature was on the continent of Africa (Libya in September, 1922).
The greenhouse effect traps heat in our atmosphere. The atmosphere lets some infrared radiation escape into space; some is reflected back to the planet.
ATMOSPHERE
The Earth's atmosphere is a thin layer of gases that surrounds the Earth. It is composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and trace amounts of other gases.
The atmosphere was formed by planetary degassing, a process in which gases like carbon dioxide, water vapor, sulphur dioxide and nitrogen were released from the interior of the Earth from volcanoes and other processes. Life forms on Earth have modified the composition of the atmosphere since their evolution.
MARS.The Red Planet
Mars, the red planet, is the fourth planet from the sun and the most Earth-like planet in our solar system. It is about half the size of Earth and has a dry, rocky surface and a very thin atmosphereMARS' SURFACEThe surface of Mars is dry, rocky, and mostly covered with iron-rich dust. There are low-lying plains in the northern hemisphere, but the southern hemisphere is dotted with impact craters. The ground is frozen; this permafrost extends for several kilometers. The north and south poles of Mars are covered by ice caps composed of frozen carbon dioxide and water. Scientists have long thought that there is no liquid water on the surface of Mars now, but recent photos from Mars indicate that there might be some liquid water near the surface. The surface of Mars shows much evidence of the effects of ancient waterways upon the landscape; there are ancient, dry rivers and lakes complete with huge inflow and outflow channels. These channels were probably caused by catastrophic flooding that quickly eroded the landscape.
Scientists think that most of the water on Mars is frozen in the land (as permafrost) and frozen in the polar ice caps.
G. Schiaparelli was an Italian astronomer who first mapped Mars (in 1877) and brought attention to the network of "canali" (Italian for canals or channels) on Mars. These "canals" were later found to be dry and not to be canals at all. A Martian impact crater (Crater Schiaparelli, 461 km = 277 mi in diameter) and a hemisphere of Mars have been named after Schiaparelli.
SIZE
Mars is about 4,222 miles (6790 km) in diameter. This is 53% (a little over half) of the diameter of the Earth.
PLANETARY COMPOSITION
Crust and Surface: Mars' surface is composed mostly of iron-rich basaltic rock (an igneous rock). Mars has a thin crust, similar to Earth's.
Mantle: Silicate rock, probably hotter than the Earth's mantle at corresponding depths.
Core: The core is probably iron and sulphides and may have a radius of 800-1,500 miles (1,300-2,400 km). More will be known when data from future Mars missions arrives and is analyzed
MASS AND GRAVITY
Mars' mass is about 6.42 x 10^23 kg. This is 1/9th of the mass of the Earth. A 100-pound person on Mars would weigh 38 pounds.
LENGTH OF A DAY AND YEAR ON MARS
Each day on Mars takes 1.03 Earth days (24.6 hours). A year on Mars takes 687 Earth days; it takes this long for Mars to orbit the sun once.
MARS' ORBIT
Mars is 1.524 times farther from than the sun than the Earth is. It averages 141.6 million miles (227.9 million km) from the sun. Its orbit is very elliptical; Mars has the highest orbital eccentricity of any planet in our Solar System except Pluto.
ATMOSPHERE
Mars has a very thin atmosphere. It consists of 95% carbon dioxide (CO2), 3% nitrogen, and 1.6% argon (there is no oxygen). The atmospheric pressure is only a fraction of that on Earth (about 1% of Earth's atmospheric pressure at sea level), and it varies greatly throughout the year. There are large stores of frozen carbon dioxide at the north and south poles. During the warm season in each hemisphere, the polar cap partly melts, releasing carbon dioxide. During the cold season in each hemisphere, the polar cap partly freezes, capturing atmospheric carbon dioxide.
The atmospheric pressure varies widely from season to season; the global atmospheric pressure on Mars is 25% different (there is less air, mostly carbon dioxide) during the (northern hemisphere) winter than during the summer. This is mostly due to Mars' highly eccentric orbit; Mars is about 20% closer to the Sun during the winter than during the summer. Because of this, the northern polar cap absorbs more carbon dioxide than the southern polar cap absorbs half a Martian year later.
Occasionally, there are clouds in Mars' atmosphere. Most of these clouds are composed of carbon dioxide ice crystals or, less frequently, of frozen water crystals.
There are a lot of fine dust particles suspended in Mars' atmosphere. These particles (which contain a lot of iron oxide) absorb blue light, so the sky appears to have little blue in it and is pink/yellow to butterscotch in color.
TEMPERATURE RANGE
Mars' surface temperature averages -81 °F (-63 °C). The temperature ranges from a high of 68° F(20° C) to a low of -220° F(-140° C). Mars is much colder than the Earth.
MARS' MOONS
Mars has 2 tiny moons, Phobos and Deimos. They were probably asteroids that were pulled into orbit around Mars.
SPACECRAFT VISITS
Mariner 4 was the first spacecraft to visit Mars (in 1965). Two Viking spacecraft landed in 1976. Mars Pathfinder landed on Mars on July 4, 1997, broadcasting photos.
DISCOVERY OF MARS
Mars has been known since ancient times.
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