Our solar system is made up of eight planets and three dwarf planets which orbit the Sun.
The Sun is a star which is similar to billions of other stars in our galaxy. The Sun is much bigger than anything else in our solar system. It is so big that more than one million Earths could fit inside it. The Sun is about 150 km away from earth. The Sun is an average sized star with a diameter of approximately 1,400,000 km. Like other stars, the Sun is a shining, burning, ball made up of hydrogen and helium gas. The energy that is generated in the core of the Sun is the source of light and heat in our solar system. It can take up to a million years for the energy produced in the Sun's core to reach the surface. The surface of the Sun or, photosphere, reaches a temperature of about 5,500
C. At night, we are able to see the planets because they reflect the light of the Sun. They do not generate their own light.
The four planets closest to the Sun are Mercury, Venus, Earth, and Mars. These four planets are called terrestrial planets. Terrestrial comes from the Latin word
which means earth or land. These four planets are called terrestrial planets because they are similar to Earth. The terrestrial planets are relatively small and are made of rocky material, and have solid surfaces like the earth. Here are some interesting facts about each of the four terrestrial planets. Mercury has a diameter of 4,880 km. Mercury circles the Sun in 87.97 days and turns on it's axis in 58.65 days. Mercury has 0 moons. Venus has a diameter of 12,104 km. Venus circles the Sun in 224.7days and turns on it's axis in 243 days. Venus has 0 moons. Earth has a diameter of 12,756 km. Earth circles the Sun in 365.2 days and turns on it's axis in 23.93 hours. Earth has 1 moon. Mars has a diameter of 6,794 km. Mars circles the Sun in 686.98 days and turns on it's axis in 24.62 hours. Mars has 2 moons.
The next four planets are very different from the terrestrial planets. These planets are called giant planets or gas planets. They are also called Jovian planets, meaning planets that are like Jupiter. The giant planets, Jupiter, Saturn, Uranus, and Neptune are much different than the terrestrial planets. The giant planets are much larger than the terrestrial planets, thus, the name. The giant planets are made mostly of gas and don't have solid surfaces. Here are some interesting facts about each of the four giant planets. Jupiter has a diameter of 142,800 km. Jupiter circles the Sun in 11.86 years and turns on it's axis in 9.8 hours. As of February, 2004, Jupiter has 63 known moons. Many of them have not been named. Saturn has a diameter of 120,000 km. Saturn circles the Sun in 29.46 years and turns on it's axis in 10.2 hours. Saturn has 34 named moons and a total of 60 as of today!. Uranus has a diameter of 51,800 km. Uranus circles the Sun in 84.01 years and turns on it's axis in 17.2 hours. Uranus has 21 named moons and 6 unnamed moons. Neptune has a diameter of 49,500 km. Neptune circles the Sun in 164.79 years and turns on it's axis in 16.1 hours. Neptune has 13 known moons. Four moons were discovered in 2002 and one in 2003 and have yet to be named.
Our solar system also has 3 dwarf planets. Pluto, Ceres, and Eris are classified as dwarf planets. A dwarf planet is a celestial body that orbits around the Sun, it is not a satellite, it has enough mass for its self-gravity to overcome rigid body forces so that it takes on a nearly round shape, but unlike planets, it has not cleared the neighborhood around its orbit. Pluto was classified as a planet for 76 years until 2006 when the 26th General Assembly for the International Astronomical Union reclassified Pluto as a dwarf planet. Pluto is small and icy very different from the terrestrial planets and the giant planets. Pluto does have a moon named Charon. The dwarf planet Eris also has a moon.
Our solar system is relatively flat, like a disk. It also has billions of smaller objects orbiting the Sun. There are comets that swing in extremely elongated orbits that take them close to the Sun and then billions of miles away from it before they head back. There are thousands of rocky asteroids that orbit between Mars and Jupiter. They are in a region of space appropriately named the Asteroid Belt. There are also thousands of small, icy bodies that orbit the Sun that are in the cold, dark area of space beyond about 7 billion miles beyond Neptune. This dark area of space is called the Kuiper Belt. The comet-like bodies found within the Kuiper Belt are called the Kuiper Belt Objects. Our solar system is surrounded by a host of icy bodies that extends almost halfway to the nearest star. This swarm of icy bodies is called the Oort cloud. Next, we'll take a look at one of the "fathers" of modern astronomy, Galileo Galilei.