Each day after the solstice brings more daylight.
Holiday lights and the season of cheer may mask the fact that the darkest day of the year is fast approaching on Dec. 21.
As the Northern Hemisphere's winter solstice approaches, here is everything you need to know about the shortest day of the year for the more than 6 billion people living north of the equator.
Thursday, Dec. 21, will mark this year's winter solstice for the Northern Hemisphere, bringing the shortest day and longest night of the year. Solstices occur twice a year when "the sun's path appears farthest north or south, depending on which half of the planet you're on," according to NASA.
Because the Earth rotates on a tilt, the winter solstice occurs when the Northern Hemisphere is tilted the furthest away from the sun, which will occur at at 10:27 p.m. ET. The reciprocal event occurs at the same time for the Earth's Southern Hemisphere, which experiences the most amount of direct sunlight.
The lack of direct sunlight on Dec. 21 makes it the shortest day of the year for those in the United States. "All locations north of the equator see daylight shorter than 12 hours and all locations south see daylight longer than 12 hours," according to NASA.
The two solstices are considered to be the start of the astronomical winter and summer seasons.
According to the National Centers for Environmental Information, the astronomical seasons are marked by solstices and equinoxes, the points at which the sun aligns over the equator. Separate from astronomical seasons, meteorological seasons split the year into three-month groups based on temperature cycles and "are more closely tied to our monthly civil calendar than the astronomical seasons are."
On the bright side, each day after the solstice in the Northern Hemisphere will get more daylight, until the summer solstice on June 20, 2024.
Ancient civilizations have recognized the significance of solstices for thousands of years. Structures like Stonehenge and the Torreon in Machu Picchu, Peru, were designed to follow the sun's path relative to the Earth, according to NASA.