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Perihelion is the closest point to the sun in a planet’s orbit. Perihelion is one of the two points of apsis on elliptical orbit. The closest point is generally called an periapsis and the farthest point apoapsis. This changes depending on the object being orbited. For orbiting satellites around the Earth, these two points are called the perigee and and the apogee. For other object the suffix changes to match that object being orbited.
As I said before the Perihelion is a point on an elliptical orbit. An elliptical orbit has two centers or foci. The apsis are the points furthest or closest to one of these points. In the case of the Solar System, the main focus is the Sun so that is why we use the terms perihelion and aphelion. However the second focus in for orbits in the Solar System in often other planets. Originally, in ancient times it was assumed that the Sun went around the Earth. However the observations and research of the astronomer Copernicus helped us to understand that the opposite is true. The really big discovery was by Johannes Kepler. He noticed that stars and planets did not move exactly as a perfectly circular orbit would predict. Based of these observations he discovered that the movement of orbiting celestial bodies are actually elliptical.
There are interesting effects that the perihelion has on the orbit of objects in the Solar System. The most obvious is that the orbital speed of objects increases as they come under the greater influence of the Sun’s gravity. A great example are comets.
The understanding of perihelion also plays an important role in human exploration. Deep space probes use the periapsis of their orbit around the sun and other planets in order to travel across long distances. The use the acceleration afforded by this combined with their own booster to perform gravity assists. Then they use aerobraking to slow down once they match the orbiting speed of the new planet. Using this method of manipulating the apsis of each orbit they are able to traverse the solar system.
Scientist also take advantage of the perihelion to better study the Sun. It helps to get closer to the sun when launching satellites and probes. In the end the understanding of the orbits around the sun make its possible for us to gain a greater understanding of our Solar System.
If you enjoyed this article there are others on the Universe Today website you might enjoy. There is an article on the distance of Uranus from the Sun. There is also an article on the possibility of Jupiter wrecking the solar system.
There are also great resource on the net. There is a great article about perihelion and aphelion on the University Corporation Atmospheric Research site. There is also another great article about aphelion and perihelion the discover magazine website.