Autumn Equinox 2024

The moment of the autumnal equinox in the northern hemisphere is defined as the exact time when the apparent geocentric longitude of the Sun's center equals 180 degrees.

More commonly, in the media and society, the autumnal equinox is associated with the day in September when the length of the day and night are approximately equal.

In 2024, the autumnal equinox will occur on Sunday, September 22, at 12:43:40.82 Coordinated Universal Time (UTC), which corresponds to 15:43:40.82 in Romania's Legal Time (UTC+3, as the country will still be observing daylight saving time).

At this moment in 2024, the geocentric latitude of the Sun's center will have a value of −0.56″, the right ascension will be 12h00min0.015sec, and the declination will be −0.52″. As can be observed from the values of the geocentric latitude and right ascension, they are close to zero and 12h, respectively. For this reason, it is often said that the Sun is positioned opposite the vernal equinox during the autumnal equinox. This statement is partially accurate and acceptable because the apparent diameter of the Sun is approximately 30 arcminutes.

The autumnal equinox for countries in the northern hemisphere corresponds to the spring equinox in the southern hemisphere.

The calendar used in Romania is the Gregorian calendar. The Gregorian calendar was designed and adopted in 1582 to prevent the drifting of dates associated with seasonal changes. Thus, according to the Gregorian calendar, the autumnal equinox will always occur between September 21 and 24. In most years, it will fall on September 22 or 23. Dates of September 21 or September 24 are less common.

For example, in 2092, the autumnal equinox will occur on September 21, marking the first time this date has been used for the equinox since the Gregorian calendar's creation.

Conversely, in 1803, the autumnal equinox occurred on September 24, also for the first time since the Gregorian calendar's inception.

Published on: Sep 21, 2024