March 20

Astronomy and seasons

The March equinox usually falls on March 20 or 21, though in rare cases it can occur on March 19. At the equinox, day and night are approximately equal in length across the globe, a geometric consequence of the Sun crossing the Earth's equatorial plane. In the Northern Hemisphere this event marks the start of spring and in the Southern Hemisphere the start of autumn. See general notes on spring, the Northern Hemisphere and the Southern Hemisphere.

Calendar context

The labeling of March 20 depends on the calendar system. Under the widely used Gregorian calendar the day count is as given above; leap years add an extra day in February, making March 20 the 80th day in those years. For more on leap-year rules see leap year resources and historical reform of the Gregorian calendar.

Observances and cultural importance

Several cultural, environmental and international observances fall on or near March 20. Commonly recognized events include:

• Nowruz, the traditional Persian New Year, celebrated at the equinox by many communities across Central and Western Asia.
• The United Nations' International Day of Happiness, which highlights well-being and societal progress.
• International Francophonie Day and various environmental awareness days such as World Sparrow Day and World Oral Health Day.

Historical and notable facts

The exact date and timing of the equinox have shifted in historical records because of calendar reforms and the difference between civil calendars and astronomical time. March 20 has been a convenient civil marker for seasonal change in modern times but the precise astronomical instant can vary by year and by location.