The solar system consists of many different celestial bodies. From the Sun to Pluto, the solar system is quite vast. Laying in the Milky Way Galaxy, the solar system is home to the gigantic star known as our Sun and a handful of planets which will be listed starting from the distance closest to the Sun. The solar system has four terrestrial planets: Mercury, Venus, Earth and Mars. It is also home to four jovian planets: Jupiter, Saturn, Uranus and Neptune. Pluto used to be classified as planet like those listed but was retitled to be a dwarf-planet back in 2006. Along with the planets and the Sun there are a variety of other objects wandering around space including the asteroid belt, located between Mars and Jupiter, and the moons of the planets.
(Artist Rendition of the Solar System, image from http://scienceclass.ning.com/profiles/blogs/1677792:BlogPost:3140)
The Terrestrial Planets: Mercury, Venus, Earth and Mars
These types of planets are made up of rock and/or metals and are usually referred to as the "inner" planets (closest to the Sun). The main feature of these planets, compared to the gaseous ones, is that they have a solid surface.
The Jovian Planets: Jupiter, Saturn, Uranus and Neptune
These planets are also called gas giants because of their composition. Also known as the "outer" planets (farthest from the Sun), these planets are mostly made up of hydrogen and helium.
Planetary Motion and Mechanics:
It is important to know how the planets behave as well as what they are composed of. How the planets move in the solar system was theorized by Johannes Kepler. He was a German astronomer who eventually created Kepler's Laws. They are as follows:
1. Every planet orbits the Sun in an ellipse. The gravity from the sun causes the heavenly bodies to go around the Sun.
2. A line drawn from the planet to the Sun will sweep out an equal area within an equal time interval. This occurs because as the planets get closer to the Sun, they speed up.
(picture to illustrate laws 1 and 2, image from http://en.wikibooks.org/wiki/General_Astronomy/Kepler%27s_Laws)
3. The orbital period of the planet squared is proportional to the semi-major axis cubed. So the farther a planet is, the longer it takes to orbit the Sun. It takes Neptune about 165 years to orbit the Sun, so no birthdays for any (if any) inhabitants on Neptune.
-P = orbital period, G = gravitational constant, M = total mass, a = semi-major axis
(graph to illustrate proportionality of orbital period and semi-major axis of each planet, including the dwarf planet Pluto, image from http://www.windows2universe.org/the_universe/uts/kepler3.html)
It is always important when studying anything to understand the basic concepts behind what is being learned. Knowing these facts will hopefully help you better grasp the knowledge of more complicated and detailed concepts of the solar system.
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