Get ready for the winter solstice: When is the shortest day of the year?

The winter solstice, occurring on December 21, marks the shortest day of the year. Ancient cultures saw it as a time of celebration, symbolizing the sun's return after long nights. In 2024, a stunning lens flare at Mt. Sinai Harbor will highlight this celestial event, offering a unique spectacle.

The winter solstice, the shortest day of the year, occurs on December 21. While many might view this as a day to endure, much like a cold spell or a particularly tough week, ancient cultures saw it in a vastly different light. To them, the solstice marked a time for celebration. It signified the moment when the sun, after enduring long nights, started its gradual return. The winter solstice was a reminder of natures cyclical power and the suns ultimate victory over the dark winter months.

On December 21, 2024, Mt. Sinai Harbor in New York will provide a remarkable display of this celestial event. A stunning lens flare, caused by the setting sun, will highlight the beauty of the solstice, adding a dramatic touch to the natural spectacle. For the ancient Romans, the winter solstice was known as "Dies Natalis Solis Invicti," or the Birthday of the Unconquered Sun. This was a major celebration in the third century AD, which featured bright lights, festivals, and chariot races. The timing of this Roman festival, which fell near December 25, eventually led to its adoption by early Christians to celebrate the birth of Jesus, despite the fact that the Bible does not specify the exact date of his birth.

The winter solstice also marks a time of limited daylight. In places like New Jersey, December 21 will bring just under nine hours of sunlight, with sunrise occurring at approximately 7:15 AM and sunset around 4:30 PM. In stark contrast, the summer solstice, which occurs on June 20, offers roughly 14 hours of daylight. For astronomers, however, the shorter days of winter are a welcome opportunity to observe the night sky earlier. Gary Swangin, an astronomer-at-large for Warren County and former director of the Newark Museum Planetarium, explains that the winter solstice is particularly advantageous for astronomers. He can set up his telescope by 5:00 PM and begin observations by 6:00 PM, while during the summer months, he has to wait until almost 9:30 PM before the sky is dark enough for viewing. "The winter solstice is truly wonderful for us," Swangin notes.

While ancient civilizations celebrated the solstice as a sign of the suns triumph over darkness, modern science provides a more nuanced explanation. The sun does not change its behavior on this day, but rather it is the tilt of the Earth that affects how sunlight is distributed across the planet. Earths axis is not perfectly perpendicular to its orbit around the sun, but rather tilted at an angle. This axial tilt, which is about 23 degrees, is responsible for the varying lengths of days and nights throughout the year.

Swangin compares the Earths tilt to the wobble of a spinning top, rather than it standing perfectly upright. Scientists believe that a colossal impact by a celestial body known as Theia, which occurred billions of years ago, not only created the Moon but also tilted the Earth at this crucial angle. This tilt means that the Northern Hemisphere experiences shorter days in December, with sunlight striking the region at a shallow angle. Meanwhile, the Southern Hemisphere, which is tilted toward the sun during this time, enjoys the longest days of the year and the beginning of summer. Swangin further highlights this contrast, explaining that in countries like Australia and New Zealand, December marks the start of summer and the longest day of the year.

Sources:

• Space.com: Winter solstice 2025 marks the shortest day of the year
• Live Science: When does winter start? Your guide to the 2025 winter solstice
• AP News: Thousands cheer as the sun rises on winter solstice at Stonehenge
• When is the shortest day of the year? Get set for the winter solstice