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How to Calculate Aphelion

Aphelion is a term used in astronomy to describe the position in a planet's elliptical orbit in relation to the sun. Specifically, aphelion is the point in a planet's orbit that is the farthest from the sun. The closest point to the sun in a planet's orbit is the perhelion. Aphelions exist because the orbits of planets around the sun are elliptical and the sun is not perfectly in the center of the orbits. The aphelion of a planet can be calculated in a few short steps.

Instructions

- 1
  Navigate the Internet to NASA's Lunar and Planetary Science website. Click on the name of the planet in the left column for which you wish to calculate aphelion.
- 2
  Click on the planet's "Fact Sheet." Under "Orbital Parameters" take note of the semimajor axis of the planet as well as the orbital eccentricity of the planet. For example, the semimajor axis of Mars is 228 million km. The orbital eccentricity of Mars is 0.093412.
- 3
  Calculate the planet's aphelion by adding 1 to the orbital eccentricity, then multiplying that number by the planet's semimajor axis. In the example, add 1 and 0.093412 to get 1.093412. Then, multiply 1.093412 by 228 million km to get an aphelion of 249.298 million km. By calculating the equation, you see that Mars is at the farthest distance in its orbit from the sun at 249.298 million km.

Astronomy