How do you find a planet's perihelion date?

Question

Elena Antonova · Accepted Answer

You can get an approximate date by adding a multiple of the planet's period to a past perihelion data. To get an accurate date requires a lot of computation.

The actual point in time when a planet is closest to its sun is known as perihelion. The anomalistic period is the interval of time between perihelion to perihelion; if the planet has a Kepler elliptical orbit, then each perihelion will happen one anomalistic period after the other. However, because of precession and other planets' gravitational pull, planets do not actually follow Kepler's elliptical orbits. Earth's perihelion happens approximately on January 3. Depending on the positions of the other planets, especially Venus and Jupiter, the actual time of perihelion can vary from January 2 to January 5. The DE430 data set is a good choice to use at the moment. Using this data and appropriate software, it is possible to calculate the moment of perihelion for any given orbit. NASA's Jet Propulsion Laboratory provides data files which allow the positions of the Sun, Moon, and other planets to be calculated with great accuracy for any time from centuries ago to centuries in the future. The following are some Earth perihelion dates: January 4, 2014, at 11:59 UTC; January 4, 2015, at 06:37 UTC; January 2, 2016 at 22:49 UTC; and January 4, 2017 at 14:18 UTC.

Hunter Arthur · Answer

undefined The perihelion date of a planet is determined by subtracting half of the orbital period from the aphelion date. To find the perihelion date of a planet, you need to know its orbital parameters, specifically its semi-major axis, its orbital eccentricity, and the date of its aphelion (when it is farthest from the sun). With this information, you can use Kepler's laws of planetary motion to calculate the perihelion date.