Solar System

You are right that planets are not the same as stars. Stars burn hydrogen fuel by thermo-nuclear fusion which means they are very hot and give off light and heat. Planets on the other had are much smaller, and only shine from reflected star light.

Objects called Brown Dwarf stars lie inbetween the two objects. They are like the planet Jupiter only much bigger. They give off some faint light, but they are not quite big enough to start shining through thermonuclear fusion.

If your looking for information on comets, take a look at this site. It contains lots of useful information, including links to other comet sites.

The Sun's effect on the Earth is extremely great. It provides the energy needed for life, creates the seasons, day and night, powers the aurora, and affects just about every other aspect of life on Earth.

It's effect on the Moon is more subtle but also large. The temperature on the Moon varies significantly over the course of a lunar day and night from boiling hot to freezing cold and back.

The most noticable effect caused by the moon is the Earth's tides. As the Moon orbits the Earth, the oceans are pushed and pulled, altering sea level and generating huge amounts of tidal energy.

The effect of the Moon and Earth on the Sun is very small, but not completely insignificant. As the planets move around the Sun, the Sun wobbles slightly due to the pull of the planets. This effect is being used by scientists to indirectly detect planets around other stars.

I'm afraid my site is only really to do with the Solar System. Try taking a look at this site which is about the Milky Way.

I'm glad you enjoyed my site. Regarding the error on the Mercury page, it might seem strange but it's not actually a mistake - although I should try to explain it better.

Mercury's orbital period is 88 Earth days, that's the time it takes for Mercury to go round the Sun once, and end up where it started.

Mercury's rotational period is 58.6 Earth days, that's the time it takes for the planet to spin about its axis 360 degrees.

Because the two values are similar, to an observer standing on the surface of Mercury, a day (from Sunrise to Sunset) would seem to take much longer than the rotation period of 58.6 days. This is because as the planet spins (causing the Sun to set) the planet moves further round its orbit (causing the Sun to rise). This is what I meant when I said that on Mercury a day is twice as long as a year.

Hope that clears things up. If you wan't a bit more information about this effect take a look at this page, it explains it a bit more clearly!

Unlike stars, which give off light of their own, planets are only visible because light from the Sun is reflected back to us here on Earth. If any planets exist beyond the orbit of Pluto, then they would be extremely faint, and even with modern telescopes we haven't managed to find anything yet.

Working out the core temperatures of the planets is more complicated.

For the outer planets, like Jupiter, which are made up of gas, we can tell how hot they are by looking at their size. The hotter you make a gas the more it expands (think about hot air balloons) so by comparing the weight and the size of the planets we can make a guess about the temperature in the core.

The inner planets, like Earth, are made of rocks and metal, so this method won't work. Also the cores of planets like Earth are heated by radioactive rocks near the centre. We have to guess how much radiation is generated by the other planets to work out the core temperature.

There is a general distinction between the inner four planets (Mercury, Venus, Earth and Mars) and the outer planets (Jupiter, Saturn, Uranus and Neptune). Pluto is a bit of an oddball and doesn't fit the pattern. In general, the inner planets, called the terrestrial are small and dense, made mostly of rock and metal and have no or few moons. The outer planets (called the gas giants) are much bigger, have large gaseous atmospheres made from hydrogen, helium, methane and ammonia and tend to have lots of satellites.

Apart from a general trend that the outer planets are colder there isn't really a fixed formula for the temperature of the planets. This is because the temperature depends on lots of factors, including the composition of the atmosphere (how well it holds heat) and how reflective it is (how quickly heat is lost).

I hope that helps, for more information about the actual values take a look at my datastore pages, which give all the numbers for temperature, distance and size for each of the planets and most of the major moons in the solar system.

Take a look at this previous question.

Take a look at this previously asked question for details of all the known moons of the Solar System.

Nine Planets by Bill Arnett has a good general Solar System overview page.

Please send me information as soon as possible, because my project is due in about 10 days.

Most of the information you need is on this site. All the facts you need can be found on the Datastore page and the facts about the Solar System can be found by clicking on the "Did you know.." links on the planet pages. For more details about Mercury, try looking at the Mercury page of Bill Arnett's Nine Planets website.

I would be happy to recommend your site to my visitors. I am current working on a links section to add to my site and I will include your page when it's done. I will have to come up to York some time to cycle your model! There is another site like yours on the web you might be interested in, by the Bradley University Physics Department.

There are quite a few sites which you may find useful. For pictures of the Solar System, try NASA's Solar System Simulator which lets you look at any of the planets, from anywhere in the Solar System at any time. For an interactive model (called an orrery) look at the Solar System Live. It shows you where all the planets are right now, and lets you change the date and time too.

I have an interactive page on this site called the Datastore which contains lots of facts and figures about the planets in the Solar System, including the distance to the Sun for each of them.

The total area inside the orbit of Pluto is roughly 13,600,000,000,000,000,000 square miles. That's more than one thousand billion times the area of the United States.

If you mean why do the planets orbit the way they do, it's because of the force of gravity. All of the planets in the Solar System, are attracted most strongly to the Sun, because it has the largest mass. This force holds them in their orbits when they would otherwise fly off into empty space.

Take a look at the "Did you know..." link on each of the planet pages for a fact on each of the planets. The Nine Planets website contains lots of facts about Mercury.