The Planets: An Overview
The word “planet” is Greek for “wanderer”. They gave them this name because as they watched the sky at night, the stars seemed to stay still. The planets, however, seemed to move in one direction and then moved backwards a little bit, and then forward again. The backwards movement is called the planet’s “retrograde”. This occurs because as we go around the sun, we will sometimes pass other planets or have them pass us. Then as our orbit changes, it appears that the planet catches back up.
There are currently 8 planets in our Solar System. The 4 planets closest to the Sun are known as the “rocky planets” and are made up primarily of rocky material. The 4 planets furthest from the Sun are known as the “gas giants” and are made up primarily of different gases, with a heavier rocky core in the middle. In between the two groups is the Asteroid Belt. A large area that includes millions of different sized bodies made up of rock and metal that float in between Mars and Jupiter. Many scientists believe that these bodies are leftover from when the Solar System first formed. Most of the material turned into planets or natural satellites, but some stuff just never found a place.
Mercury: Mercury is the closet planet to the Sun. It has the smallest orbit and so moves the fastest around the Sun. It is important to remember that the closer to the Sun, the faster the orbit, and the shorter the solar year. Mercury is the Roman name for Hermes, the messenger god with winged shoes. He was fast, and so is Mercury as it orbits the Sun. Mercury is currently the smallest planet. It is 36,000,000 miles from the Sun. A day on Mercury is the same as almost 60 Earth days and a year on Mercury is the same as almost 88 days. So, as you can see, a day is almost the same as a year on Mercury. Mercury has no natural satellites.
Venus: Venus is the second closest planet to the Sun. Venus is the Roman name for Aphrodite, the goddess of love and beauty. The planet was so named because it looked pretty. Venus is the sixth largest planet just behind Earth and is located 108,200,000 km (67,230,000 miles) from the Sun. A year on Venus is about 225 Earth days, but a day on Venus is about 243 Earth days, making a day on Venus actually longer then a year. Venus has no natural satellites.
Earth: I am going to skip Earth for now, as all of our comparisons are based on the Earth.
Mars: Mars is the fourth planet from the Sun. It is named for the god of war because of it’s red color. Mars is the second smallest planet, behind only Mercury. It is 227.9 million km (141.6 million miles) from the Sun. A day on Mars is about 24.6 Earth hours, almost a day, and a year on Mars is the same as 687 Earth days, almost two years. Mars has two satellites, Phobos and Deimos.
Jupiter: Jupiter is the fifth planet from the Sun, behind the Asteroid Belt and Mars and is mainly known for the Big Red Spot spinning through it’s cloudy atmosphere. Jupiter is the largest planet in the Solar System and is 778,330,000 km (480,000,000 miles) from the Sun. A day on Jupiter is about 10 Earth hours and a year on Jupiter is about 12 Earth years. Jupiter currently has 67 natural satellites, the four largest are known as the “Galilean Moons” because they were first observed by Galileo through his “telescope”. They are, in order from biggest to smallest,: Ganymede, Callisto, Io, and Europa.
Saturn: Saturn is the sixth planet from the Sun and is known for it’s rings (even though all of the gas giants have them to some extent). Saturn is the second largest planet next to Jupiter and is 1,400,000,000 km from the Sun. A day on Saturn is about 10 Earth hours and a year on Saturn takes about 30 Earth years. Saturn has somewhere between 53 and 62 natural satellites.
Uranus: Uranus is the seventh planet from the Sun and is known for lying on it’s side within it’s orbit. Most planets rotate in a perpendicular fashion according to their orbit, but Uranus is lying on it’s side and orbiting that way. Uranus is the third largest planet in the Solar System and is about 3,000,000,000 km (1,770,000,000 miles) from the Sun. A day on Uranus is about 18 Earth hours and a Uranus Year takes about 85 Earth years. Uranus has 27 known natural satellites.
Neptune: Neptune is the eighth and final “official” planet in the Solar System and the fourth largest. It lies about 4,500,000,000 from the Sun. A day on Neptune is about 19 Earth hours and a year on Neptune is about 165 Earth years. Neptune has about 13 natural satellites.