By Montserrat Arqué
Jun 20, 2024, 3:32 PM EDT
This June 20, 2024, astronomy lovers and the general public will witness a rare event: the earliest summer solstice in 228 years. This astronomical phenomenon not only marks the official start of summer in the Northern Hemisphere, but also reveals the fascinating intricacies of our calendar and its relationship to celestial movements.
The summer solstice is the time when Earth’s north pole reaches its maximum tilt toward the Sun. This astronomical event results in the longest day and shortest night of the year in the Northern Hemisphere. Traditionally, the solstice occurs around June 21, but in 2024, it will surprise us with its early arrival.
Summer solstice 2024 will be a historic event
The summer solstice of 2024 will occur on June 20 at 4:50 p.m. (ET). To put this in perspective, the last time the solstice occurred this early was in 1796, when George Washington was president of the United States and the French Revolution was in full swing.
The explanation for this unusual timing lies in the differences that exist between the Gregorian calendar and the real movement of the Earth around the Sun. Some key factors are:
1) The actual length of the solar year: A solar year lasts approximately 365.242189 days, not exactly 365 days.
2) The Gregorian calendar: To compensate, this calendar averages 365.2425 days per year by using leap years.
3) Leap years: Every 4 years, we add an extra day (February 29), making the solstices occur approximately 18 hours earlier than the previous year.
4) Turn of century rule: Years ending in “00” are only leap years if they are divisible by 400 (for example, 2000 was a leap year, but 1900 was not).
The combination of these factors produces a cumulative effect that results in the early solstice of 2024.
This phenomenon is not an isolated event. For the next 72 years, the summer solstice will continue to occur progressively earlier every 4 years. By 2096, the solstice is projected to occur at 2:32 a.m. (ET) on June 20, before the cycle resets and the dates begin to move backwards.