The Washington PostDemocracy Dies in Darkness

The winter solstice arrives Wednesday. These 5 maps explain the shortest day of the year

Low winter sun over Reagan National Airport on Dec. 16. ( <a href="">Joe Flood via Flickr</a> )

It’s certainly felt like winter in much of the country these last few weeks. And if you’re a weather enthusiast, winter already began on Dec. 1. However, if you prefer the traditional, astronomy-based definition, then winter officially begins with the solstice, at 5:44 a.m. Eastern time on Dec. 21.

For those of us in the Northern Hemisphere, the winter solstice marks the shortest day and longest night of the year.

If you’re an avid sun observer, or just want to learn more about the solstice, have a look at these five maps to learn more:

1. Solstice day and night world map

This map projection of the Earth shows how dark the Northern Hemisphere is at the time of the winter solstice, 5:44 a.m.

Because the Earth’s axis of rotation is tilted 23.5 degrees, each hemisphere receives different amounts of sunlight as our planet orbits the sun.

The December solstice occurs when the sun’s direct rays reach their southernmost position with respect to Earth’s equator. At that moment, the sun shines directly overhead at 23.5 degrees south latitude, along the Tropic of Capricorn (this year, the sun will be straight overhead in southern Africa when the solstice arrives).

Since the sun’s direct rays reach their southernmost point with respect to Earth’s equator, the December solstice brings us the southernmost sunrise and sunset of the year. In the Northern Hemisphere, we see the sun take its lowest and shortest path across the southern sky. That means if you catch a glimpse of the sun at local noon, your shadow will be the longest of the year.

2. Daylight hours on the winter solstice

The solstice is the shortest day of the year, but how long is the sun up where you live? This map — the first of four created by Alaska-based climatologist Brian Brettschneider — shows how daylight hours vary with latitude across North America:

A good portion of the Lower 48 sees the sun up for nine to 10 hours on the winter solstice, leaving about 14 to 15 hours of nighttime (see chart).

In Washington, the sun is up for 9 hours and 26 minutes (rising at 7:23 a.m. and setting at 4:49 p.m.). That’s about an hour less daylight than in South Florida, but still an hour longer than in cities across the Northern Tier, like Minneapolis and Seattle.

Of course, our long winter night pales in comparison to Alaska, where the sun barely climbs above the horizon for three to four hours in much the Last Frontier. North of the Arctic Circle — at 66.5°N latitude — the sun never rises, and darkness prevails as the Earth rotates on its axis.

3. Difference in daylight between summer and winter

This next map shows how daylight balances out over the course of a year. The higher one’s latitude, the greater the change in daylight from summer to winter:

Along the midsection of the Lower 48 — along a line stretching roughly from San Francisco to Washington — there are about five and a half fewer daylight hours on the winter solstice than on the summer solstice in June.

Cities at lower latitudes, such as Atlanta and Dallas, see less variation in daylight between the longest and shortest day of the year (only about four and a half hours). Further north, in Chicago and Boston, the difference amounts to over six hours. Then there’s extreme Alaska, where nighttime is anywhere from 12 to 24 hours longer now than it was six months ago.

4. Time of the earliest sunset

The shortest day of the year means dusk arrives early. While our earliest sunsets are already behind us (more on that in map No. 5), this map presents a time-zone adjusted view of sunset times in the United States and Canada just before the solstice.

In gray regions — which includes Washington and the Mid-Atlantic — the earliest sunsets are between 4:30 and 5 p.m. Light yellow regions encompass the cities of Chicago, Boston and Seattle, where the sun sets between 4 and 4:30 p.m. In purple areas, the earliest sunsets are not until after 5 o’clock.

One thing we can glean from this map is the combined effect of time zones and latitude on sunset times. The color contours are slanted from northwest to southeast because the Earth’s northern hemisphere is tilted away from the sun during winter.

Pick any two points on the map within the same time zone and draw a line between them. Anytime you move north and east, sunset arrives earlier, while moving south and or west means sunset will be later.

5. Earliest sunset and latest sunrise not on the solstice 

Although the winter solstice marks the shortest daylight period in the Northern Hemisphere, it’s not the day of the latest sunrise or earliest sunset, as this final map shows. In fact, most places in the mid-latitudes see their earliest sunset two weeks before the solstice, while the latest sunrise isn’t until early January.

What causes this astronomical oddity, though?

The succinct explanation is that solar noon — the time the sun reaches its highest point in the sky each day — moves several minutes later in December, a phenomenon caused by Earth’s planetary tilt and elliptical orbit around the sun. When the sun takes more than 24 hours to reach the same point in the sky from one day to the next, we start to see a lag between our 24-hour clocks and the sun’s apparent daily motion in the sky. This discrepancy pushes sunrise and sunset times later even as the days continue to shorten right up until the solstice.

Note from this map how the dates of the earliest sunset and latest sunrise change with distance from Earth’s equator. At higher latitudes, the earliest sunset and latest sunrise happen closer to the solstice, while in lower latitudes they can be well over a month apart.

In Washington, sunset on the solstice is already 3-4 minutes later compared to the earliest sunset of the year, which came around Dec. 7. Meanwhile, sunrise will continue to advance for the next two weeks, with the latest sunrise not until Jan. 5.

But even though our latest sunrise and earliest sunset don’t neatly coincide with the shortest day of the year, remember that the days will slowly start to get longer now. So if the dark days of winter are getting to you, rest assured, it only goes up from here — and that’s something to celebrate.