A dangerous winter storm and punishing Arctic blast are brewing, but if you’re longing for more sunlight, Wednesday is a day to celebrate: Dec. 21 is the winter solstice, the shortest day and longest night of the year – and first day of astronomical winter – in the Northern Hemisphere. It’s a sign that longer, brighter days are upon us.
The second and final solstice of 2022 arrives within about an hour of sunset across the eastern third of the United States, at 4:48 p.m. Eastern time.
What happens on the solstice?
During the winter solstice, the sun appears directly over the Tropic of Capricorn, a line of latitude 23.5 degrees south of Earth’s equator. At this moment, the sun’s daily southward movement in the sky appears to pause, and the sun rises and sets at its southernmost points on the horizon.
In the Northern Hemisphere, we see the sun take its lowest and shortest path across the southern sky. The low sun angle means you will cast your longest midday shadow of the year on the winter solstice (assuming skies are clear).
Why do we have solstices?
Solstices, equinoxes and seasons occur because the Earth doesn’t orbit the sun completely upright. Instead, Earth’s axis is tilted by about 23.5 degrees, which causes each hemisphere to receive different amounts of sunlight throughout the year.
“The Earth’s axis always points the same direction, so as the planet makes its way around the sun, each hemisphere sees varying amounts of sunlight,” Capital Weather Gang’s Jeremy Deaton explained in a 2019 article.
In December, the Northern Hemisphere is tilted away from the sun, bringing us less direct sunlight and colder weather. Meanwhile, in the Southern Hemisphere, Dec. 21 marks the first day of summer and the longest day of the year.
Halfway between the winter and summer solstices are the equinoxes, when the length of day and night are nearly equal everywhere on Earth.
While the winter solstice marks the first day of astronomical winter, meteorologists define winter as the coldest three calendar months of the year, running from Dec. 1 to the end of February.
How much daylight do we see on the solstice?
Daylight hours on the winter solstice depend on latitude: The closer you move toward the North Pole, the less time the sun spends above the horizon. On Dec. 21, Miami and Houston see more than 10 hours of daylight, while in Seattle and Minneapolis, the sun is up for less than 9 hours.
Washington, D.C., has 9 hours 26 minutes of daylight on the winter solstice, with sunrise at 7:23 a.m. and sunset at 4:49 p.m., according to timeanddate.com.
Farther north, the short days become even more extreme. Anchorage, sees only 5 hours 28 minutes of daylight, while in Fairbanks the sun spends a scant 3 hours 41 minutes above the horizon. The Arctic Circle marks the line where the sun no longer rises on the winter solstice.
Why are the latest sunrise and earliest sunset not on the solstice?
Though the winter solstice has the shortest period of daylight, it’s actually not the day of the latest sunrise or earliest sunset. For example, Washington’s earliest sunset was at 4:45 p.m. on Dec. 7, while the latest sunrise is at 7:27 a.m. on Jan. 5.
This misalignment happens because Earth is tilted on its axis, and we orbit the sun in an ellipse, not a perfect circle. Together, these two factors cause our 24-hour clocks to get slightly out of sync with the length of the “solar day” – the amount of time it takes the sun to reach its highest point in the sky from one day to the next. While humans measure days in 24-hour increments, the “solar day” is not exactly 24 hours.
Near the December solstice, each solar day runs about 24 hours and 30 seconds long. That means it takes a bit longer than 24 hours for the sun to appear in the same place in the sky from one day to the next. The lag time starts to add up over a few weeks, causing both sunrise and sunset times to shift slightly later each day, even as the days keep getting shorter until Dec. 21.
The exact dates of the earliest sunset and the latest sunrise also depend on your latitude. In most of the Lower 48, the earliest sunset and the latest sunrise occur about two weeks before and after the solstice, respectively. Closer to the Arctic Circle, the earliest sunset and latest sunrise happen on or near the winter solstice.
The bottom line: mornings will get a bit darker until early January, but we’ve already gained a few minutes of evening light. On balance, daylight will start to increase after Dec. 21, even as winter’s coldest days still lie ahead.