The planets of our solar system are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto is no longer considered a planet. The first four, Mercury, Venus, Earth, and Mars, along with the Asteroid Belt, are termed the "Terrestrial Planets" or the Inner Solar System.
The second group of planets are known as the "Gas Giants." These include Jupiter, Saturn, Uranus, and Neptune. Pluto, a dwarf planet, is part of what is now known as the Kuiper Belt (pronounced Ki-Per). This field of icy debris, approximately 8 billion miles from the Sun, is also known as the final frontier of our Solar System. The debris in the Kuiper Belt are also known as transneptunian objects, or TNO for short.
It is easy to remember the order of the eight planets from the sun by creating a mnemonic aid. For example, "Merry Vincent Eats Mary's Jelly Sandwiches Until Noon. In this way, the first three letters of "Merry" go with "Mercury", and the first three letters of "Mary's" go with "Mars," in order to not mix up Mercury and Mars.
The Terrestrial Planets
Mercury is the second smallest planet but closest to the Sun. Its distance also makes it the hottest planet. Its gravity on the surface is about one-third of the Earth's. Mercury's orbit takes it around the Sun approximately every 88 Earth days. Mercury revolves slowly: one day here is equal to almost 59 Earth days. It can be seen with binoculars or even the naked eye.
Venus is the second from the Sun and closer to Earth's size. It is inhospitable to life at 864° F and almost 100 times more gravity pressure than Earth's. The atmosphere is almost entirely carbon dioxide with a cloud base of sulfuric acid surrounding it. Besides the sun and the moon, Venus is next brightest. It is often mistaken for a star in the morning and evening.
Earth is third from the sun. Seventy percent of the Earth's surface is covered with water, the only planet having water in its liquid phase on the surface of the planet. Earth is the only planet known to be hospitable to life.
Mars, the smallest planet, appears mostly red, hence it is also known as the Red Planet. At half Earth's diameter it is only about a tenth of Earth's mass and one third of Earth's gravity. It has a harsh, inhospitable climate, averaging -67° F. It's atmosphere is mostly carbon dioxide. At night, Mars is easily visible with the naked eye. With a telescope, it is possible to see details like its canals and two moons.
The Gas Giants
Jupiter is the fifth planet from the sun and the largest of the planets. Jupiter is a large ball of gas with no terrestrial (land) surface. It is extremely large, 318 times the mass of Earth. Gravity, when measured at the top of the atmospheric clouds is about 2.5 times Earth's gravity. One day on Jupiter is only around 10 hours, and it takes 12 Earth years to orbit the sun. It is often seen with the naked eye, but with binoculars or a telescope, its giant red spot or rings may be seen.
The second largest planet in the Solar system is Saturn. Saturn is made up of primarily gas with a small rocky core. It is most famous for its rings. Saturn appears to the naked eye as a small yellow object, but when viewed with a telescope, some of the rings are easily visible. Under very good conditions at least two more rings can be seen. Very strong telescopes will distinguish more rings, as well as the nine moons orbiting Saturn.
Uranus is seventh in line from the sun. It has a mass almost 15 times greater than Earth's, with a volume that is 67 times greater. Uranus has a rocky core, completely covered with water, mixed with rocky particles. Its atmosphere consists of hydrogen, helium, and methane. Gravity is not that much different from Earth, although it spins fast: its day is only 17 Earth hours. Uranus is so far from the sun, that its year is 84 Earth years. Uranus has at least 11 rings and 15 moons.
The last of the Gas Giants is Neptune, the fourth largest planet. It is similar to Uranus with its rocky core and water as well as size and atmospheric composition with some minor differences. A day on Neptune lasts only 16 Earth hours, but its yearly orbital around the sun takes nearly 165 Earth years. It has 4 rings.
This was just a quick overview of the solar system and planetary basics. The study of the Solar System is constantly filled with new discoveries as more and more information is discovered and transmitted back to Earth.
References
Greene, Nick. Accessed on April 29, 2010 About.com
Lyon, Jene Astronomy: Our Sun and Its Neighbors. Western Publishing Company, Racine Wisconsin, 1974
Rachel Schaus - Rachel Schaus, contributing writer,Minnesota-based freelance writer who has written hundreds of articles relating to classical education, ...
