New Delhi: Marking the beginning of spring in the Northern Hemisphere, day and night will be of equal duration on Monday.

According to the Science Popularisation Association of Communicators and Educators (SPACE), Monday will mark the Vernal Equinox.

The event known as equinox is eagerly awaited by space enthusiasts as it takes place only twice a year, on March 21 and September 23.

"The name equinox is derived from the Latin word aequus (equal) and nox (night), because around the equinox, the night and the day are approximately equally long. An equinox happens twice each year, occurring approximately around March 20/21 (Vernal) and September 22/23 (Autumnal)," a SPACE statement said.

"An equinox happens when there is a location on the earth's equator where the centre of the sun can be observed to be vertically overhead. This year the Vernal Equinox is on March 21," it added.
On the equinox, the sun moves across the celestial equator, which lies directly above the Earth's equator.

When the Sun crosses the plane, it rises exactly in the east and sets exactly in the west.

"This year the phenomenon (vernal equinox) will take place at 4:51 am (23:21 UT)," SPACE president Chander Bhushan Devgun said.

On the occasion, SPACE will be conducting a public outreach programme at Jantar Mantar to explain to people the concept of equinox using ancient instruments.

Space enthusiasts would observe equinox day on Monday by taking measurements of the shortest shadow at noon and also calculate the latitude of the place.