In India, the shortest day (and longest night) of the year occurs on about:

Around 21 or 22 December, the Northern Hemisphere has its shortest day and longest night. This date is the winter solstice for the Northern Hemisphere, including India.

What happens on the winter solstice:

• The Sun's rays fall vertically on the Tropic of Capricorn (23.5 degrees South) at noon.
• The Northern Hemisphere is tilted farthest away from the Sun, so the Sun appears lowest in the sky at noon and the days are shortest.
• Areas north of the Arctic Circle have continuous darkness for 24 hours (polar night).

In the Southern Hemisphere, it is the summer solstice, with the longest day of the year. Areas south of the Antarctic Circle have 24 hours of daylight.

Length of the day in India on this date:

• Places in northern India, such as Delhi, have about 10 hours 15 minutes of daylight.
• Places in southern India, closer to the Equator, have a longer day, about 11 hours or more, because day length varies less near the Equator.

The summer solstice:

• Around 21 June, the Sun is overhead at the Tropic of Cancer.
• The Northern Hemisphere then has its longest day and shortest night.
• This is the summer solstice for the north and the winter solstice for the south.

Meaning of "solstice":

The word comes from the Latin "sol" (Sun) and "sistere" (to stand still), because the Sun appears to pause in its northward or southward movement before reversing direction.

Festivals linked with the solstices:

Many cultures celebrate the winter solstice. In India, Makar Sankranti in mid-January marks the Sun's movement into the zodiac sign Capricorn (Makar) and the beginning of longer days, though the actual solstice now falls about three weeks earlier.

Why not the other options?

• ✗21 June is the longest day in the Northern Hemisphere (summer solstice).
• ✗21 March and 23 September are the equinoxes, when day and night are nearly equal.