New! Sign up for our free email newsletter.
Reference Terms
from Wikipedia, the free encyclopedia

Solstice

A solstice is a key astronomical event that happens twice a year, marking the times when the Sun appears at its most extreme positions—either farthest north or farthest south—relative to Earth’s equator. These events occur because of Earth’s axial tilt of about 23.5 degrees. As our planet orbits the Sun over the course of a year, this tilt causes different parts of Earth to receive varying amounts of sunlight. The solstices are the two moments when that tilt results in either the longest or shortest day of the year, depending on your location.

In the Northern Hemisphere, the Summer Solstice occurs around June 20 or 21. On this day, the Sun travels its longest path across the sky, resulting in the most daylight hours of the year. Conversely, the Winter Solstice, usually around December 21 or 22, brings the shortest day and longest night, as the Sun follows its lowest and shortest arc through the sky. In the Southern Hemisphere, these events are reversed—summer begins in December, and winter in June.

The word "solstice" comes from the Latin sol (Sun) and sistere (to stand still), referring to the way the Sun appears to pause in its movement before reversing direction. Although solstices mark the official beginning of summer or winter, they don’t necessarily coincide with the warmest or coldest weather, because Earth’s land and oceans take time to heat up or cool down—a phenomenon known as seasonal lag.

Solstices have held deep cultural and spiritual significance throughout human history. Ancient monuments like Stonehenge in England and Newgrange in Ireland were built to align with solstice sunrises or sunsets. The Inca festival Inti Raymi celebrates the winter solstice in Peru, and many winter holidays in the Northern Hemisphere, such as Yule and Christmas, are closely tied to the idea of light returning during the darkest time of the year.

In contrast to solstices, equinoxes occur when day and night are nearly equal in length, but solstices emphasize the extremes: the longest and shortest days. Together, solstices and equinoxes form the framework of Earth’s seasonal cycle, offering a cosmic rhythm that has shaped agriculture, ritual, and human understanding for millennia.

Related Stories
 


Earth & Climate News

August 27, 2025

Ancient forests may have fueled a deep-sea oxygen boost nearly 390 million years ago, unlocking evolutionary opportunities for jawed fish and larger marine animals. New isotopic evidence shows that this permanent oxygenation marked a turning point ...
Even sharks’ famous tooth-regrowing ability may not save them from ocean acidification. Researchers found that future acidic waters cause shark teeth to corrode, crack, and weaken, threatening their effectiveness as hunting weapons and ...
A research team created a plant-inspired molecule that can store four charges using sunlight, a key step toward artificial photosynthesis. Unlike past attempts, it works with dimmer light, edging closer to real-world solar fuel ...
Researchers uncovered that the Maui wildfires caused a spike in deaths far higher than reported, with hidden fatalities linked to fire, smoke, and lack of medical access. They warn that prevention rooted in Native Hawaiian ecological knowledge is ...
A new study reveals that the majority of Earth’s species stem from a few evolutionary explosions, where new traits or habitats sparked rapid diversification. From flowers to birds, these bursts explain most of the planet’s ...
As the ozone layer recovers, it’s also intensifying global warming. Researchers predict that by 2050, ozone will rank just behind carbon dioxide as a driver of heating, offsetting many of the benefits from banning ...
Industrial forests, packed with evenly spaced trees, face nearly 50% higher odds of megafires than public lands. A lidar-powered study of California’s Sierra Nevada reveals how dense plantations feed fire severity, but also shows that proactive ...
Planting more trees can help cool the planet and reduce fire risk—but where they are planted matters. According to UC Riverside researchers, tropical regions provide the most powerful climate benefits because trees there grow year-round, absorb ...
Kelp forests bounce back faster from marine heatwaves when shielded inside Marine Protected Areas. UCLA researchers found that fishing restrictions and predator protection strengthen ecosystem resilience, though results vary by ...
Scientists found that Great Salt Lake’s chemistry and water balance were stable for thousands of years, until human settlement. Irrigation and farming in the 1800s and a railroad causeway in 1959 ...
NASA-backed simulations reveal that meltwater from Greenland’s Jakobshavn Glacier lifts deep-ocean nutrients to the surface, sparking large summer blooms of phytoplankton that feed the Arctic food ...
NASA and ISRO s NISAR satellite has just reached a major milestone: the successful deployment of its enormous 39-foot antenna reflector in orbit. Folded up like an umbrella during launch, the reflector is now fully extended and ready to support ...

Latest Headlines

updated 12:56 pm ET