Southward Equinox

Overview

This is the approximate date and time of this year's Southward Equinox. In the Northern Hemisphere this is known as the Fall Equinox. In the Southern Hemisphere it is known as the Spring Equinox. It is the time when the length of the day and night are equal all over the planet and the solar declination is heading southward.

Info

The Southward Equinox is an important starting point or anchor point in many calendars. It usually occurs around September 20th. Over time, roughly in a cycle of 25,772 years, Earth's axes precess, causing the equinoxes and solstices to slowly drift through the entire year.

Accuracy

The accuracy of this calculation depends on the precision of Meeus's calculations. On top of that, my solutions don't exactly match those provided by Meeus, either due to Javascript's base-2 calculations or due to misinterpreting steps such as adding Terrestrial Time. Overall these results are very close, usually within a few minutes of reality.

Source

This calculation was sourced from Astronomical Algorithms (1991) by Jean Meeus.

This cycle can be calibrated using the ephemerides at this website.