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Autumnal Equinox – Fall Equinox

Equinoxes are opposite on either side of the equator, so the autumnal (fall) equinox in the Northern Hemisphere is the spring (vernal) equinox in the Southern Hemisphere and vice versa.

Equinox and solstice illustration.

Equinoxes and solstices happen twice a year.

Equinoxes and solstices mark the start of astronomical seasons. The equinoxes start spring and fall, while solstices start astronomical summer and winter.

Not Entirely Equal Day & Night

On the two equinoxes every year the Sun shines directly on the Equator and the length of day and night is nearly equal – but not exactly.

The September equinox marks the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from north to south and vice versa in March.

When is the Equinox in my City?

Southern Hemisphere Autumnal Equinox

(Australia, New Zealand, South America, southern Africa)

Northern Hemisphere Autumnal Equinox

(USA, Central America, Canada, Europe, Asia, northern Africa)

First Day of Fall?

In the Northern Hemisphere, the fall equinox marks the first day of fall (autumn) in what we call astronomical seasons. There's also another, more common definition of when the seasons start, namely meteorological definitions, which are based on average temperatures rather that astronomical events.

Topics: Astronomy, Sun, Seasons, September, March, Calendar, Equinox

In This Article

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Astronomical Season Calculator


Sunrise & Sunset Times

Winter & Summer Solstices

  1. What is the June Solstice?
  2. Facts about June Solstice
  3. What is the December Solstice?
  4. Facts about December Solstice
  5. When is the Summer Solstice?
  6. When is the Winter Solstice?
  7. June Solstice Celebrations
  8. December Solstice Celebrations
  9. What Causes Seasons?

Equinox & Solstice Worldwide

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Equinox and solstice illustration.

When is Spring Equinox?

The Vernal (Spring) Equinox in the Northern Hemisphere is in March. In the Southern Hemisphere, it's in September. more

September equinox illustration

September Equinox

The Sun shines directly at the Equator on the September equinox and the length of day and night is nearly equal, but not quite. more