Does You Know About Longest Day of the Year : Summer Solstice 2023
New Delhi (Weather) – June 21 marks the summer solstice, a remarkable event in which the northern hemisphere experiences the longest day of the year (while the southern hemisphere experiences the shortest). In India, cities like Ujjain and Gandhi Nagar witness a zero shadows moment when shadows disappear at noon.
But what exactly does a solstice mean, and why does the longest day of the year fall on this particular date? Listed below are answers to such interesting frequently-asked questions on the summer solstice.
What does a solstice mean?
Every day, during the journey between sunrise and sunset, the Sun’s position relative to that of the Earth changes from east to west. However, the Sun also undergoes a similar yet slightly less apparent movement throughout the year — from north to south.
While the latter movement is difficult to spot every day, the difference can be clearly observed over time by noting the Sun’s position from a fixed point on the Earth (like your home).
But for two days every year, the Sun appears to ‘stand still’ as it pauses on the northern and southern limits before changing direction. These days are called the solstices, with the word being derived from Latin sol (“sun”) and sistere (“to stand still”).
These ‘pause days’ occur once in the summer (around June 20-22, depending on your time zone) and once in the winter (by December 21-22).
What causes the Sun’s north-south movement?
The Sun’s north-south movement relative to the Earth’s position occurs due to our planet’s axial tilt. But what does axial tilt mean?
If you draw an imaginary line through Earth’s north and south pole, the line isn’t exactly vertical. Rather, the Earth has a tilt of roughly 23.5 degrees off its imaginary vertical axis, and this is referred to as the axial tilt. This tilt causes the two hemispheres to be either towards or away from the Sun and its direct sunlight at different times of the year.
As the Earth revolves around the Sun, the most direct sunlight keeps shifting between the Tropic of Cancer and the Tropic of Capricorn through the year. This is what causes the change of seasons, as the hemisphere facing the Sun experiences summer while the other half witnesses winter.
How does the summer solstice occur?
In technical terms, the summer solstice marks the farthest tilt of the Sun towards the north of the Earth.
On the summer solstice day for the northern hemisphere, the Sun’s location is directly above the Tropic of Cancer. The north pole is tilted about 23.4° towards the Sun, which makes the rays fall directly overhead of the Tropic of Cancer, whose latitude is roughly the same 23°3’ N.
In simpler words, when the summer solstice takes place in the northern hemisphere in June, the north pole is as tilted towards the Sun as it can be, while the south pole is as far away from it as possible.
This day also marks the beginning of the Sun’s southward movement, which is also known as the Dakshinayan in India. From here on and for the next six months, the Sun will change its position and move towards the south pole. And in six months’ time, the Sun will appear directly overhead of the Tropic of Capricorn, whose latitude is 23.5°S, thereby marking the winter solstice.
Why do we have solstices?
Solstices, equinoxes and seasons occur because Earth doesn’t orbit the sun completely upright. Instead, Earth’s axis is tilted by about 23.5 degrees, which causes each hemisphere to receive different amounts of sunlight throughout the year.
In June, the Northern Hemisphere leans toward the sun, bringing us more direct sunlight and warmer weather. Meanwhile, in the Southern Hemisphere, June 21 marks the first day of winter and the shortest day of the year. Halfway between the winter and summer solstices are the equinoxes, when the length of day and night are nearly equal everywhere on Earth.
While the summer solstice marks the first day of astronomical summer, meteorologists define summer as the warmest three calendar months of the year, spanning June, July and August.
Approximate sunset time on the summer solstice. pic.twitter.com/nVU2CNb4A7
— Brian Brettschneider (@Climatologist49) June 21, 2023