Summer solstice: Why June 21 will be the longest day of the year in Northern Hemisphere

At New Delhi, sunrise will be at 5:23 am and sunset at 7:21 pm, the day length being 13:58:01.

At New Delhi, sunrise will be at 5:23 am and sunset at 7:21 pm, the day length being 13:58:01. Representative image. (Express photo: Tashi Tobgyal)

The longest day of 2021 for those living north of the Equator is June 21. In technical terms, this day is referred to as the summer solstice, the longest day of the summer season. It occurs when the sun is directly over the Tropic of Cancer, or more specifically right over 23.5 degree north latitude. This will happen around 9:02 am on Monday (Indian Standard Time).

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Why do we have summer solstice?

Since Earth rotates on its axis, the Northern Hemisphere gets more direct sunlight between March and September over the course of a day, which also means people living in the Northern Hemisphere experience summer during this time. The rest of the year, the Southern Hemisphere gets more sunlight.

During the solstice, the Earth’s axis — around which the planet spins, completing one turn each day — is tilted in a way that the North Pole is tipped towards the sun and the South Pole is away from it.

Typically, this imaginary axis passes right through the middle of the Earth from top to bottom and is always tilted at 23.5 degree with respect to the sun. Therefore, the solstice, as NASA puts it, is that instant in time when the North Pole points more directly toward the sun that at any other time during the year. Solstice means “sun stands still” in Latin.

This day is characterised by a greater amount of energy received from the sun. According to NASA, the amount of incoming energy the Earth received from the sun on this day is 30 per cent higher at the North Pole than at the Equator.

The maximum amount of sunlight received by the Northern Hemisphere during this time is usually on June 20, 21 or 22. In contrast, the Southern Hemisphere receives most sunlight on December 21, 22 or 23 when the northern hemisphere has its longest nights– or the winter solstice.

How many hours of sunlight will we get on Monday?

The amount of light received by a specific area in the Northern Hemisphere during the summer solstice depends on the latitudinal location of the place. The further north one moves from the equator, the more light one receives during the summer solstice. At the Arctic Circle, the sun never sets during the solstice.

At New Delhi, sunrise will be at 5:23 am and sunset at 7:21 pm, the day length being 13:58:01. Further south in Mumbai, sunrise will be at 6:02 am and sunset at 7:18 pm, and the day length will be lower at 13:16:20. Even closer to the equator in Chennai, sunrise will be at 5:43 am, sunset at 6:37 pm, and day length lowest among major cities at 12:53:48.

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Summer solstice does not mean the earliest sunrise or latest sunset

Although June 21 will be the longest day in 2021, it does not necessarily mean that it brings the earliest sunrise or latest sunset. It depends on the latitudinal location of the country.

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