When is Earth closest and furthest from the Sun?

(by Amara Graps)

You may notice that the sunrise times continue to happen later in the day and the changes for a longer day in the other direction don't occur until *after* the winter solstice. (In other words, it is not until sometime in January that the days actually start getting longer.)

The geometry of the Earth in its eccentric orbit around the Sun, along with its 23.5 degree tilt of its spin axis may be hard to visualize.

Note that the longest and shortest days of the year incorporate the axis tilt and other factors having to do with how we have our Julian calendar defined, but the Earth's axis tilt has nothing to do with how close or how far the Earth is to the Sun.

You can calculate these values from the book: _Astronomical Algorithms_ by Jean Meeus, but the US Naval Observatory has already done that. So you can find the dates/times of perihelion (when the Earth is closest to the Sun) and aphelion (when it is furthest) at

http://aa.usno.navy.mil/data/docs/EarthSeasons.php

Note that the perihelion and aphelion dates are *not* constant year to year.

Are these dates and the Winter and Summer solstaces constant in their relationship to each other decade to decade?

There's a several-day jitter in the date of perihelion and aphelion from year to year. Now the equinoxes and solstices vary by +/- 1 day, as we go through the leap-year.

The longitude of perihelion (when Earth closest to the Sun) is changing with time, the date of perihelion shifts by ~1 day in 58 years. The precession carries the equinox and solstice points westward with time, too and we tie the calendar to those, so I believe that they are constant in their relationship to each other decade to decade.

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Special Thanks to A. Graps