The September equinox marks the beginning of autumn in the Northern Hemisphere
The September equinox, also called southward equinox, is the moment in time (not a day-long event) when the Sun stands directly above the equator while crossing from the north to the south. For the Northern Hemisphere (where nearly 90% of the world's population live) it is the autumn equinox
) as it is the moment when summer
ends and autumn
) begins, while for the Southern Hemisphere it is the vernal equinox
), the moment when winter
ends and spring
begins. Up until the September equinox the Sun rises and sets more to the north of the equator, and afterwards it rises and sets more to the south.
The September equinox usually occurs every year between September 21 and 24
. The dates given on this page are based on Coordinated Universal Time (UTC), which for practical purposes is equivalent to Greenwich Mean Time (GMT - the time zone of the United Kingdom). While the September equinox occurs at the same moment in time all over the world, the date and local time differ from place to place depending on the year and a location's time zone. For locations that are ahead of UTC (further east) it may fall on the day after, and for locations that are behind UTC (further west) it may fall on the day before. To find out the exact date and time of the September equinox 2021 in your area use this seasons calculator
The September equinox is one of four days (two equinoxes and two solstices) throughout the year that mark the beginning of a new season. The other days are the March equinox
, the June solstice
and the December solstice
The word "equinox" is derived from Latin and means "equal night". On the day of an equinox, day and night are of approximately equal length all over the world, as the Earth's rotational axis is neither tilted away from nor towards the Sun. At all other times the length of day and night will be different.
The exact moment of the September equinox through the centuries
Graph demonstrating the movement (caused by leap shifting) of the exact moment of the September equinox between 1900 and 2520. X axis (bottom, horizontal): Calendar years, Y axis (left, vertical): day in September (21 to 23).
In a non-leap year, the moment of the September equinox is about 5 hours 49 minutes after
that moment in the previous year (in UTC), and in a leap year
it is about 18 hours 11 minutes before
that moment in the previous year, as can be seen in this graph. In this way the time of the September equinox constantly shifts back and forth so it always stays between September 21 and 24. This four year cycle is clearly visible in the graph.
To adjust for the gradual movement backwards on the calendar (as visible for the period 1900 to 2099), in years divisible by 100 (1900, 2100, 2200, 2300 and 2500 on the graph), which should be leap years as they are divisible by 4, the leap day is omitted (except when they are divisible by 400, eg. 2000 and 2400) and the moment of the September equinox moves forward in time compared to the same moment in the year before.
Overview: seasons, equinoxes and solstices
Dates shown apply to the Northern Hemisphere and are based on UTC (GMT)
2021 calendar as templates for
Word, Excel and PDF
A selection of calendar templates for 2021 in landscape and portrait orientation and with US federal holidays, suitable for a variety of applications.