Planets

A planet as defined by the International Astronomical Union (IAU), is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

The term planet is ancient, with ties to history, science, myth, and religion. The planets were originally seen by many early cultures as divine, or as emissaries of the gods. Even today, many people believe in astrology, which holds that the movement of the planets affects people's lives, although such a causation is rejected by the scientific community. As scientific knowledge advanced, human perception of the planets changed, incorporating a number of disparate objects. Even now there is no uncontested definition of what a planet is. In 2006, the IAU officially adopted a resolution defining planets within the Solar System. This definition has been both praised and criticized, and remains disputed by some scientists.

The planets were thought by Ptolemy to orbit the Earth in deferent and epicycle motions. Though the idea that the planets orbited the Sun had been suggested many times, it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations, performed by Galileo Galilei. By careful analysis of the observation data, Johannes Kepler found the planets' orbits to be not circular, but elliptical. As observational tools improved, astronomers saw that, like Earth, the planets rotated around tilted axes, and some share such features as ice-caps and seasons. Since the dawn of the Space Age, close observation by probes has found that Earth and the other planets share characteristics such as volcanism, hurricanes, tectonics, and even hydrology. Since 1992, through the discovery of hundreds of extrasolar planets (planets around other stars), scientists are beginning to understand that planets throughout the Milky Way Galaxy share characteristics in common with our own.

Planets are generally divided into two main types: large, low-density gas giants, and smaller, rocky terrestrials. Under IAU definitions, there are eight planets in the Solar System. In order from the Sun, they are the four terrestrials, Mercury, Venus, Earth, and Mars, then the four gas giants, Jupiter, Saturn, Uranus, and Neptune. The Solar System also contains at least five dwarf planets: Ceres, Pluto (originally classified as the Solar System's ninth planet), Makemake, Haumea and Eris. With the exception of Mercury, Venus, Ceres and Makemake, all of these are orbited by one or more natural satellites.

There are 344 known extrasolar planets, ranging from the size of gas giants to that of terrestrial planets.

Planets in our galaxy

According to the IAU's current definitions, there are eight planets in the Solar System. In increasing distance from the Sun, they are:

1. Mercury
2. Venus
3. Earth
4. Mars
5. Jupiter
6. Saturn
7. Uranus
8. Neptune

If you are having problems remembering the planets in their correct order, just remember this sentence "My very educated mother just served us nine pickles," Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

Fun Facts About Our Planets

There will be many things to see in the night sky. Unfortunately, it's nearly impossible to describe them with out pictures. You will have to go to the library and get a few books on locating the wonders above our heads.

One thing I can do for you is to provide you with some fun facts about our solar system. Let's find out how long a year is by reading the list below. On one planet your birthday would arrive every 88 days!!! On another planet you would not live to see your first birthday!

Mercury

• Orbits the Sun in 88 Days. Thats a pretty short year!
• 2.On the other hand each Mercury day is equal to 59 Earth days. This is because it takes 59 days for Mercury to rotate on its own axis.
• Mercury is the only planet whose orbit is coplanar with its equator. Venus and Uranus are the only planets that rotate opposite to the direction of their orbit.

Venus

• Orbits the Sun in 224 Days.
• Each Venus day is equal to 243 Earth days. This is because it takes 243 days for Mercury to rotate on it's own axis.

Earth

• Orbits the Sun in 365 Days.
• Turns on it's own axis every 24 hours. Actually it takes about 23 hours and 56 minutes to turn on it's axis.

Mars

• Orbits the Sun in 687 Days.
• Turns on it's own axis every 24 hours and 37 minutes.

Jupiter

• Orbits the Sun in 11.9 Earth Years. Now that is a LONG Jupiter year.
• Turns on it's own axis every 9 hours and 50 minutes. The days are short but the years are sooo long.
• Jupiter has the shortest day of all the planets. Although it has a circumference of 280,000 miles compared with Earth's 25,000 Jupiter manages to make one turn in 9 hours and 55 minutes.

Saturn

• Orbits the Sun in 29.5 Earth Years.
• Turns on it's own axis every 10 hours and 14 minutes.

Uranus

• Orbits the Sun in 84 Earth Years.
• Turns on it's own axis every 15 hours and 14 minutes.
• Uranus' axis is at 97 degrees. which means that it orbits on its side. (Most of the planets spin on an axis nearly perpendicular to the plane of the ecliptic but Uranus' axis is almost parallel to the ecliptic.)

Neptune

• Orbits the Sun in 164.8 Earth Years. This is the planet in which you would never see your first birthday.
• Turns on it's own axis every 16 hours and 3 minutes.

Pluto

• Orbits the Sun in 248.6 Earth Years.
• Turns on it's own axis every 6 days and 9 minutes. On pluto time practically stands still!
• Pluto is no longer classified as a planet.

The three most recently discovered planets were Uranus in 1781, Neptune in 1846, and Pluto in 1930.