I’ll be honest: I always thought that solstice lasted an entire day. But the Met Office explained that it’s actually a “very specific moment which is over almost as soon as it has begun”. “Solstice” comes from the Latin for “sun standing still” and refers to a moment in which the sun appears to stall in the sky. This year, the winter solstice will happen on December 21 at 8:50am GMT. It’s the astronomical opposite of the equinox (the next of which is due on Wednesday, 23 September at 1:04am GMT ). Here’s what the word means, as well as what’s actually happening in the sky when the phenomenon occurs. What does equinox mean? Equinox comes from two Latin words: “aequus”, meaning “equal”, and “nox, which means “night”. Given that daytime and nighttime last roughly the same amount of time in an equinox, the name’s pretty apt. There is, however, another day when light and dark hours are exactly even. This is called an “equilux” and happens “a few days before the spring equinox and a few days after the autumn equinox,” per the Met Office. What is an equinox? The Earth is tilted at an angle, which is why we have seasons. If we weren’t angled, the amount of light we get throughout the year would stay stable. This means that there will be a point in the year where the North Pole is the closest, or furthest away, it’ll be to the sun in that cycle. This is a solstice (either the longest or shortest days). Meanwhile, an equinox happens when the sun is as close as possible to the equator. This is why night and day seem equally divided: the amount of light we recieve depends on our angle in relation to the sun, so with minimal tilt, sunshine is divided about evenly. Without that slant, the Earth would have an equinox everyday. So why isn’t an equinox the same as an equilux? If you remember from earlier, the day in which we actually get equal sunlight is called an “equilux,” not an “equinox”. Robert Massey, deputy executive director of the Royal Astronomical Society, told the BBC this is because sunlight has to get through Earth’s atmosphere before it reaches us. “This means when the sun’s near the horizon it appears to be slightly higher than it is because the light is refracted through the atmosphere. So, you get slightly longer than the 12 hours of sunlight,” he explained. Related... I Just Learned The Actual Meaning Of 'Solstice', And I Had No Clue Yep, Pooping In Space Is Just As Weird As You Think Scientists Made A 'Once In A Century' Moon Discovery During A Routine Check