# Perihelion dates and parameters

I have to find the perihelion and aphelion data for the 20th century for Earth. I found this table http://www.astropixels.com/ephemeris/perap2001.html, but no such table for the past century.

I think it can be found using JPL Horizons web interface, but can not use the code (the boundaries of the task I was given) and do not want to check 36000+ entries by eye to find maximums and minimums: this is not the general way to solve the problem.

I believe that there is some relationship between Keplerian elements and perihelion (argument of periapsis or mean anomally) but after checking the file from JPL Horizons I could not find any such relationship. Therefore, I have two questions:

1) Is there an archive with the dates of peryhelion and aphelion in the past?

2) What is the relationship between Keplerian elements and the perihelion (of course, if such exists)? Unfortunately, I was not able to find it from the picture on https://en.wikipedia.org/wiki/Orbital_elements. More precisely, is it true that argument of periapsis or mean anomally is equal to 0 at the perihelion?

In googling I stumbled across the following list of Perihelion dates and times back through the beginning of the twentieth century, and forward to then end of the twenty-first.

This seems to agree with the values generated by the US Naval Observatory's Perihelion and Aphelion page, which accepts individual years as values. (Site is kind of fickle on Mondays for some reason; perhaps scheduled downtime.)

Mean Anomaly, for an elliptical orbit, can be thought of as the quasi-angular parameter representing the angle swept since the time of periapsis of a hypothetical object in a circular orbit with the same radius as the semimajor axis of the elliptical orbit. As such, yes, it will always be 0 when your actual object is at periapsis.

Argument of Periapsis, on the other hand, is the angle measured in the plane of the orbit, from the Ascending Node to the Periapsis of the orbit, in the direction of travel around the orbit. It remains the same regardless of the position of the object in the orbit. As such, it will only be 0 at periapsis when the Ascending Node and the Periapsis are the same point.

• Since Earth's $i \approx 0$, some sources give longitude of perihelion $\varpi = \Omega + \omega$. Sep 9 '19 at 19:12