Our Astounding Universe

The quick answer? Stars are big balls of gas. They are made up of mostly Hydrogen and Helium, which are the lightest elements in the universe. Their color depends on their surface temperature. Dark red stars are the least hot and blue stars the hottest. White dwarf stars can vary in temperature. There are an amazing amount of stars in space, as a matter of fact, there are more stars in the universe than there are grains of sand on Earth. Want to see more Hubble Images?

Watch How Stars are Born and Die on How Stuff Works.

Yep, the Sun is a star, but you probably already knew that. The Sun is a dwarf star. The sun spots are not entirely understood by scientists, but it is known that they are cooler than the rest of the sun, and are caused by an interaction with the sun's magnetic sphere. The Sun's magnetic sphere also causes solar flares and solar wind.

Watch The Sun and Solar Flares on How Stuff Works.

Well, we used to have 9 planets, but Pluto got demoted and is now a dwarf planet. They are in order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. You will get a chance to learn about each one individually as you travel down this page.

If you want loads of real time information on our own moon, you've got to try this Lunarphase software.

Learn How the Andromeda Galaxy Works on How Stuff Works.

Mercury is the closest planet to the sun and is about 1/3 the size of Earth, making it the smallest planet in our solar system. Mercury has no moon. Mercury orbits the Sun faster than any other planet, but has the second slowest rotation. One day on Mercury is the same as 58 days 16 hours on Earth. One year is 87.9 days, so one day on Mercury last almost a whole year. Okay kids, bedtime...but mom, it's still light outside!

Venus is the 6th largest planet and except for the Sun and Moon, is the brightest object in the sky. The orbit of Venus is the most circular and its retrograde rotation is slow, with one Venus day being equal to 243 Earth days.
The atmosphere of Venus is mostly carbon dioxide and has extremely thick clouds of sulfuric acid. These have caused a greenhouse effect which gives Venus a surface temperature of about 420°C, hot enough to melt lead. The surface of Venus is actually hotter than that of Mercury even though Mercury is closer to the Sun. Venus has no magnetic field and no moon.

Earth is the only planet whose name is not derived from mythology. The Earth's core is probably mostly iron, but that is theoretical, and the center of the core is thought to be hotter than the surface of the Sun. Earth is the only planet with tectonic plates. Liquid water covers 71% of the Earth's surface and is the only planet on which water can exist on the surface in liquid form. A combination of Earth's solar wind, magnetic field, and atmosphere cause the auroras. Earth has only one official satellite, called the Moon.

Mars, called the Red Planet, has the most varied terrain of all the planets. With a mountain over 14 miles high, a valley around 2485 miles long, a crater over 3 1/2 miles deep, and a unique bulge 2485 miles across. Mars has ice and solid carbon dioxide caps at both poles, also known as "dry ice"; therefore, there may be liquid water beneath the dry ice. Mars is the 6th largest planet and has two satellites: Phobos and Deimos, which mean Fear and Dread.

Watch The Mountain of Mars on How Stuff Works.

Jupiter is the largest planet in our solar system. It is so large that over 1,000 Earths could fit inside. Jupiter is a gas planet, meaning it has no solid surface, and is nearly 90% hydrogen and 10% helium, with other trace elements. Jupiter probably has a rocky core equal in mass to 10-15 Earths, with the main bulk of Jupiter being liquid metallic hydrogen. Jupiter has high velocity winds which are confined in bands, with adjacent bands always blowing in the opposite direction. The Great Red Spot is large enough to hold two Earths and is an area of high pressure. Jupiter has very faint small rings which probably come and go because of Jupiter's large gravitational and magnetic fields. Jupiter has 4 large moons: Io, Europa, Ganymede, and Callisto , and so many small moons that they haven't all been named.

Saturn is the least dense of the planets and is made up of about 75% hydrogen and 25% helium with other trace elements. If one found a body of water large enough, Saturn would actually float. Saturn also has unique auroras. Saturn has a liquid metallic hydrogen interior, rocky core, and molecular hydrogen layer, similar to Jupiter. Saturn's rings are extremely thin and made up of mostly ice particles. Saturn has 34 "named" moons, with the six largest moons being: Titan, Rhea, Iapetus, Dione, Tethys, and Enceladus. Learn about these at the Major Moons of Saturn.

Uranus is the 3rd largest planet and is composed of mostly rock and different ices. It is so tilted on it's axis, that the magnetic field is not centered on the planet and there is a debate as to which pole is it's north pole. Uranus has a blue color and also has 11 known faint rings. It takes 84 Earth years to make one orbit around the Sun. Uranus has 21 "named" moons. Learn about five of the moons of Uranus: Oberon, Titania, Umbriel, Ariel, and Miranda, at The Major Moons of Uranus.

Neptune is the 4th largest planet and since the orbit of Pluto is eccentric, there are times when Neptune is farther from the sun than Pluto. Neptune is similar to Uranus in composition and like Uranus has a blue color due to the absorption of red light because of methane in it's atmosphere, but what causes it to have such a rich blue tint is unknown. Neptune has the fastest winds in the universe, about 1,242 MPH. Neptune also has faint rings, with one of them looking oddly twisted. Neptune has three major moons: Triton, Proteus, and Nereid, though little is known about Proteus and Nereid, especially compared to the major moons of the other planets. Learn about them at the Major Moons of Neptune.

Asteroids are the large pieces left over from the formation of planets and are mostly found in the asteroid belt between the orbits of Mars and Jupiter.

Comets are particles of dust and frozen water and/or gas that are also left over from the formation of solar system. When the comet's orbit brings them close to the sun, the frozen ice vaporizes releasing the trapped dust particles which produces the sparkling "tail".

Meteroids are pieces that have broken off the asteroids or comets, and travel in their own orbits around the sun.

Meteors are the "shooting stars" that began as meteoroids, but burn up in the Earth's atmosphere.

Meteorites are the meteoroids that do not completely burn up in the atmosphere and survives impact with the surface of the Earth.

Watch asteroids and meteoroids on How Stuff Works.

Gamma Rays, discovered by French physicist Henri Becquerel in 1896, are the most energetic forms of light and have the smallest wavelengths known to man. These rays are produced in the hottest regions in the universe by nuclear explosions, supernova explosions, and the decay of radioactive materials. They can travel over vast distances and are absorbed, thankfully, by the Earth's atmosphere. These rays can be a danger to all life on Earth since they kill living cells, but doctors use this ability to their advantage by using Gamma Rays to kill cancerous cells. The difference in Gamma Rays and X-rays are that Gamma Rays form in the nucleus of an atom and X-rays form in the electron fields surrounding the nucleus and are produced by machinery.

Watch this excellent explaination on How Stuff Works.

Scientists know there are "Holes" in the universe, but they believe there could be holes of different sizes, worm holes where you can travel across vast distances in mere minutes, and white holes, which are the opposite of black holes. While white holes and worm holes have never been found, the theories exist.