The winter solstice falls on Dec. 21, 2018, the moment at which Earth’s axis tilts the Northern Hemisphere farthest from the sun’s warmth. It happens once a year in each hemisphere. The winter solstice is particularly special this year as the upcoming December full moon, named the Cold Moon, will be visible in the night sky along with the Ursid meteor shower.

What is the winter solstice?

The winter solstice, also known as midwinter, is the shortest day of the year and the longest night of the year. It occurs when the sun appears at its most southerly position. The earliest people on Earth built monuments to follow the sun’s yearly progress, for example, Stonehenge in England. At sunrise at Stonehenge on the longest day of the year, the rising sun appears behind one of the main stones, creating the illusion that the sun is balancing on the stone. Stonehenge was closed for 16 years after rioting broke out between police and revelers for several years at solstice gatherings. The site was reopened to the public on the solstice in 2000.

When is the winter solstice and how long is it?

This astronomical event officially arrives Friday at 5:23 p.m. EST. At this time of year, each day is about 24 hours, 30 seconds long. It’s because Earth is nearing its closest point to the sun in its elliptical orbit.

Why winter solstice 2018 is unique:

1) December full moon

The moon will appear full both Friday and Saturday nights. The names of the moon originate from the Native Americans, who marked December’s full moon as the beginning of the coldest part of the year. The Long Night Moon is named after the longest night of the year on the winter solstice.

2) Ursid meteor shower

The American Meteor Society says the Ursids should be visible in the mid-Northern Hemisphere. At the peak there should be about 11 sporadic meteors per hour just before dawn. The shower gets its name because its meteors appear to emanate from Ursa Minor, also known as the Little Dipper. Unfortunately, due to the aforementioned full moon, the meteors might be hard to spot.

3) Mercury/Jupiter conjunction

In the southeast before sunrise Friday, you can see Mercury and Jupiter appearing as if they’re about to collide in space, despite being hundreds of millions of miles apart. They will be 0.9 degrees apart, which is about two moon-diameters. They will only be visible in a sky illuminated by bright twilight.