Anomalistic Year

Anomalistic Year[1]

A year is not necessarily a year. “Annual” means yearly, but what is a year? There are actually 6 different years: Anomalistic year, Draconitic year, Julian year (this one you are familiar with — 365.25 days), Luna year, Sidereal year, and Tropical year.

The Anomalistic year is the time Earth takes to travel from one perihelion (closest to the Sun) to the next perihelion. This is shown in the figure above. All the years might be the same if everything moved in gear-like fashion, and the Sun were fixed.

The Anomalistic year is actually 365.259636 days. Now that isn’t Earth shaking to be sure, but it is slightly longer than the Julian year we are used to, by 0.009636 days.

The chart below shows the lengths of each of the years in days.

Draconitic 346.620075883
Lunar 354.370000000
Tropical 365.242189000
Calendar 365.250000000
Sidereal 365.256363004
Anomalistic 365.259636000

It surprises people that our common conception of how to measure time is not precisely fixed, and there is the question: “A year is a year is a year?”

[1] Cosmos – The SAO Encyclopedia of Astronomy,


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