People throughout history have marked the equinox and the solstice. It’s really not when the day and the night are of equal length, although that’s what we think of-it’s really that moment is when the sun is on the Equator at local noon,” says Matthew Holman, an astrophysicist at Harvard University. “The equinox is defined as the time of an event. It changes with distance from the Equator-which is why the poles have endless day in summer and months of night in winter. What's more, the length of daylight is not the same everywhere on Earth. This discrepancy is partly due to an optical illusion: Earth’s atmosphere bends light, making the sun look like it’s above the horizon when it’s really below-just like a pencil stuck in a glass of water can look like it’s been split in two at the water line. Instead, day will seem a little longer than night. Photograph by Gerd Ludwig, National Geographic After long court battles, access to the monument is now granted during winter and summer solstices, and the spring and autumn equinox. Until the beginning of the new millennium, access to the monument itself was strictly prohibited. It's actually different by several minutes in some cases,” says Milisavljevic.Īt the autumn equinox, neo-druids and Arthurian friends gather at Stonehenge to perform rituals. And on the equinox, derived from the Latin for 'equal night,' day and night are the same length-roughly speaking. Night and dayĪt the solstices in June and December, we celebrate the longest and shortest days of the year. And if you’re seething about summer’s end, consider moving closer to the Equator.

So, if the chillier air and crispier leaves have you happily reaching for pumpkin-flavored everything, thank Earth’s tilt-not its distance from the sun. “If the light is angled, it’s not going to be as hot.” “What it has to do is the amount of light per square centimeter that’s falling on you,” says Dan Milisavljevic an astronomy professor at Purdue University. At the same time, the southern half of Earth is tilted away from the sun and catches its rays at an angle, causing the cooler, shorter days of winter.Įarth is bathed evenly in sunlight only twice a year, on the equinoxes. When the planet's Northern Hemisphere is tilted toward the sun, sunlight hits it head on, bringing summer’s heat and longer days. So if it’s not Earth’s changing proximity to the sun, what gives us seasons? It's all in the slant: Earth's axis isn’t straight up and down relative to the sun, but tilted at a slight angle of about 23.5 degrees.Īs Earth revolves around the sun, it maintains that tilt, and the sun’s light doesn't hit the entire surface directly. “So in the northern winter-in December-the sun is actually closest to the Earth by a small amount, and in the summer it’s actually farther away.”

“The Earth’s orbit is about 3 percent out of round,” explains Jay Holberg, a senior research scientist at the lunar and planetary lab at the University of Arizona. The Harvard grads-captured forever in 1980s hair and their caps and gowns-were wrong. After all, Earth’s orbit isn’t a perfect circle. With varying degrees of confidence, the students explain that the Earth gets warmer or colder based on its distance from the sun. In a grainy video, a group of newly fledged Harvard graduates is asked why we have seasons.

Want to know why equinoxes happen, what to expect, and how they have been celebrated through the ages? We've got you covered. Even though an equinox happens twice a year, every year, there are a lot of misconceptions about this seasonal transition. (See gorgeous pictures that celebrate the arrival of fall.)įor the other half of the planet, September 22 is the vernal equinox, signaling the beginning of spring. The Northern Hemisphere blew by the longest day of the year with June’s summer solstice and is now coming up to the fall equinox on September 22, 2020-the day when the sun passes directly over Earth’s Equator.

Equinox 2020