Aphelion
Written by Tega Jessa
Aphelion is the farthest point of a planet's orbit around the Sun. This occurs because orbits around stars are normally elliptical. That is, they have an ovoid shape. Originally astronomers thought that the orbits of the planets were perfectly circular. However the observations of the planets never quite matched the calculations the astronomers did. This was eventually remedied by two major discoveries. First was the work of Copernicus who disproved the standard theory of the geocentric or Earth Centered model of the classical universe that was proposed by the Hellene philosopher Ptolemy. This radically changed our understanding of how planets and other celestial bodies in the observable region of space move. This established the heliocentric model where the sun is the central figure of our solar system while the Earth orbits around it.
This discovery was then followed by the observations of other astronomers, namely Johannes Kepler, who discovered the Laws of Planetary Motion. These laws were essentially a set of equations and observations that helped advance our knowledge of the orbits of celestial bodies. For one, we discovered that an orbiting planet has two foci instead one. This gives the planets their elliptical orbits. The further out you go the more eccentric the orbit becomes. The reason why this occurred was later explained with the discovery of gravity of Issac Newton. We then came to understand that succeeding planets exert their gravity acting as a second focus to the sun creating more elliptical orbits as you go further away from the sun.
The aphelion has many interesting effects on the earth. For one, the orbital velocity of the Earth slows down as it reaches its aphelion. It also has an effect on the climate. Due to the point in its orbit the Earth climate is made cooler and warmer in the Northern and Summer Hemisphere creating milder or more severe seasons. Some scientist hypothesize that major climate shifts like the Ice Ages are caused in part by major shifts in the Earth's Orbit which can alter its apsis points.
Aphelion also plays an important part in the movement of comets as the have the most eccentric orbits around the sun. The aphelion is a term only to describe the furthest point of orbit for a planet from the Sun but there are other orbits in space that work under the same principle. The name for it overall is called apoapsis. However the prefix is changed depending on the objects whether there are stars, planets, moons, or even comets.
If you enjoyed this article there are many others on Universe Today that you can enjoy. There is a great article on the orbit of Mars. There is also an interesting article on the Earth's distance from the sun.
You can also listen to the 12/12/08 Questions Episode of Astronomy Cast.
Filed under: Astronomy
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