By Jamie Carter
December 20, 2018

Winter is coming. You may have noticed that the cold season has been here for a while, but astronomically speaking it only begins with the arrival of the solstice. That happens this Friday when the northern hemisphere has its shortest day, and longest night, of the year. This year it occurs very close not only to a full moon but to a full supermoon. So it will be possible to watch an almost-full supermoon rise in the east, and a sunset in the west, very close to winter solstice. It will also be the longest full moon of 2018.

Winter solstice 2018 time and date

Winter solstice in the northern hemisphere (and summer solstice in the southern hemisphere) occurs on Friday, Dec. 21, 2018 at 5:23 p.m. EST/2:23 pm. PST. At that exact time, the sun is above the Tropic of Capricorn.

What is the winter solstice?

During winter, the northern hemisphere is tilted away from the sun, so it gets less sunlight. The sun is also lower in the sky and takes a shorter path through the sky. So it’s around for less time, and it's less intense. Cue cold temperatures in the northern hemisphere despite the fact that Earth will actually be the closest it gets to the sun on Jan. 3, 2019.

The winter solstice marks the moment when the Sun is above the Tropic of Capricorn, after which the days begin to get longer. So winter solstice is generally celebrated for being the rebirth of the sun and as the beginning of the solar year.

When is the full cold moon?

The moon will be full at 12:48 p.m. EST/9:48 p.m. PST on Saturday, Dec. 22, 2018, when the sun and the moon will be on exact opposite sides of Earth. Since that happens during the day in North America it won’t be possible to see it when it’s 100 percent illuminated. That’s not a problem, however, because when it's full, the moon is so bright that it’s almost impossible to look at. By far the best time to view the full moon is as it rises, which is at 4:47 p.m EST in New York and 5:09 PST in Los Angeles on Dec. 22. However, it takes about 10-15 minutes for the moon to climb high enough above the horizon to be visible, so you don’t need to get in position exactly on time.

Is the full cold moon a supermoon?

Opinion is divided on whether the full cold moon of 2019 is in fact a supermoon or not, largely because there is no definite definition of what a supermoon is. Visually, it’s when the moon looks larger in the sky than normal, though it’s a slight effect. It’s caused by the moon’s slightly elliptical orbit of Earth, which means that sometimes it’s particularly close. On Dec. 22, the moon will be 363,368 kilometers from Earth, making it the third closest full moon of 2018.

How to see the winter solstice

The winter solstice is not normally a visual phenomenon. However, 2018 does offer a chance to appreciate it visually because the exact time of the solstice is close to sunset and moonrise. Those in New York can see a 99.6-percent full moon rise at 3:53 p.m. EST, and a sunset at 4:31 p.m. EST, with winter solstice celebrated at 7:23 p.m. EST. In Los Angeles, winter solstice is at 2:23 p.m. PST, with a 99.6-percent full moonrise at 4:12 p.m. PST and a sunset at 4:47 p.m. PST.

How to see the full cold supermoon

To see the full cold supermoon when it's 100-percent illuminated, look east on Dec. 22 at 4:47 p.m EST in New York/5:09 p.m. PST in Los Angeles to see the moon rise. Try to find somewhere with a good view low to the eastern horizon to watch a delicately colored orange supermoon appear.

The winter solstice signals the rebirth of the sun, and in 2018 you can celebrate it shortly before witnessing both a sunset and a supermoonrise.