Article Posted on : - Dec 21, 2009

Illumination of Earth by Sun on the day of winter solstice on northern hemisphere. A file photo

NEW DELHI (PTI): December 21st is the shortest day of winter. It is a day when the Earth's axis tilts the farthest from the Sun and is called winter solstice, a term derived from Latin words 'sol' (sun) and 'sistere' (to stand still).

A solstice is an astronomical event which happens twice each year, when the tilt of the Earth's axis is most inclined toward or away from the Sun, causing the Sun's apparent position in the sky to reach its northernmost or southernmost extreme, Science Popularisation Association of Communicators and Educators (SPACE) President C B Devgun told PTI.

On the day of winter solstice, North Pole points directly away from the Sun and South Pole points directly towards the Sun, he said, adding the Sun shines at lowest heights in Northern skies and at maximum heights in Southern skies.

This results in the shortest day in the Northern Hemisphere, but at the same time it's the longest day in Southern Hemisphere.

Devgun said winter solstice indicates peak of the cold season. After this, the length of the day starts increasing and it reaches a point where day and night become equal in length at Vernal or Spring Equinox. The day continues to grow longer till summer solstice, the longest day, he added.

The winter solstice will be at 23.17 pm on Monday. In Delhi, sunrise will be at 7.10 am and sunset at 5.29 pm making it a day which is about 10 hours in duration, Devgun said.

A Khagol Mela on winter solstice has been planned by SPACE in collaboration with Nehru Planetarium at Jantar Mantar in the city.

Students from various schools would be performing activities like measuring the sun's angle during noon and finding declination of the sun using Jai Prakash Yantra at Jantar Mantar on the day.