Summer Solstice 2024: When Is The Longest Day Of The Year? Know Date, Origin, And The Science Behind It

Summer Solstice marks the longest day in the Northern Hemisphere due to Earth's axial tilt, resulting in maximum daylight and warmer temperatures until the September Equinox.

Monuments like Stonehenge in England were constructed to align with the Sun's movements, particularly during solstices.

Summer Solstice 2024: The Northern Hemisphere will witness its longest day of the year with the arrival of the astronomical summer, marking the Summer Solstice. This celestial event, commonly referred to as the June Solstice, usually takes place on either June 20 or June 21. It marks the start of astronomical summer in the Northern Hemisphere and indicates the commencement of astronomical winter in the Southern Hemisphere.

This year, the astronomical summer will arrive at 4:51 pm EDT (2:21 am IST, Friday, June 21) on Thursday, June 20, according to Space.com.

What Is Summer Solstice?

The Summer Solstice occurs due to Earth's axial tilt, which positions the Northern Hemisphere to receive the maximum sunlight of the year. This results in the Sun tracing its highest and longest path across the sky, leading to extended daylight hours and warmer temperatures. The gradual shortening of days that follows continues until the September Equinox, which marks the start of astronomical fall in the Northern Hemisphere.

The period between the June Solstice and the September Equinox spans approximately 93.6 days, according to timeanddate.com.

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Astronomical Significance Of Summer Solstice

The Summer Solstice signifies the start of astronomical summer and brings an end to astronomical spring in the Northern Hemisphere. At local noon on this day, the Sun appears almost directly overhead. A solstice is hence a precise moment when the Sun reaches its farthest point north in the sky.

Post-solstice, the Sun begins its journey southward, gradually leading to shorter days. NASA notes that during this period, a solar day — defined as the time Earth takes to rotate on its axis so that the Sun returns to the same position in the sky — exceeds 24 hours.

Earth’s 23.5-degree axial tilt is the primary reason for seasonal changes. During the Northern Hemisphere's Summer Solstice, the North Pole is tilted most directly towards the Sun, resulting in days being longer than 12 hours north of the equator and shorter than 12 hours south of it.

Despite being the longest day of the year, the Summer Solstice is not typically the hottest day. Parts of India, for example, are expecting a bit of relief today after reeling under highest ever day and night temperatures.  

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Historical And Cultural Significance Of Summer Solstice

The Summer Solstice has fascinated civilisations for millennia. Approximately 2,200 years ago, the ancient Greeks utilised this event to estimate Earth's circumference with impressive accuracy. Eratosthenes, a Greek scholar, measured the difference in shadows cast by poles in two cities 800 kilometres apart to conclude that Earth had a circumference of about 40,000 km — a figure remarkably close to the actual measurement.

Monuments like Stonehenge in England and Machu Picchu in Peru were constructed to align with the Sun's movements, particularly during solstices. 

At Stonehenge, the arrangement of the Sarsen stones and the positioning of trilithons served as a solar calendar, helping to track the passage of days within a year. A study published in March 2022 elaborated on the function of Stonehenge's calendar system, noting its basis on a tropical solar year of 365.25 days.

In Egypt, during the construction of the great pyramids and the Sphinx, the Summer Solstice played a crucial role in aligning these structures. Observers standing at the Sphinx on the solstice would see the Sun set directly between the two pyramids, an architectural marvel that reflects the ancient Egyptians' understanding of celestial events.