Everything to know about the spectacular winter solstice moon

Winter solstice moon
Public Domain Max Pixel

How fitting that on the longest night of the year, the moon will be shining brightly.

We’re seeing a lot of reports of a winter solstice full moon this year, and although the moon will be really really close to full on the shortest day of the year, December 21, she does not reach peak fullness until December 22.

The moon will still appear beautifully full enough on the solstice, even it’s not as rare as if it were officially full. The Farmer's Almanac has been tracking heavenly events and seasonal changes since 1793, and they note that the moon has been full on the winter solstice just 10 times in the Northern Hemisphere. It won’t happen again until 2094.

But that doesn’t mean the sky and the planet’s favorite little satellite won’t be spectacular on the solstice – here’s what to know.

The solstice moon will look full

Given that the moon on the winter solstice will be at 99.5 percent illumination, most people would be hard-pressed not to think it's the actual full moon. Illumination of 98 percent or more appears as a full moon.

We’ve got syzygy!

Although this term sounds more like it should be the name of Mister Mxyzptlk’s pet, it actually describes the precise moment in time when the moon is full. It is the instant when the sun and the moon are on opposite sides of Earth, marking syzygy of the Sun-Earth-Moon-system. For this month's full moon, it happens at 12:49 p.m. EST on December 22.

Plenty of moon to see

Around the full moon phase, the moon is visible in the sky generally from sunset to sunrise. Given the very long nights around the winter solstice – in New York City, the 21st will deliver a mere 9 hours, 17 minutes, and 18 seconds of daylight! – it means that the near-full and full moon will be in the night sky for a long time.

What to call her?

I love that we have names for the full moon – we can't hide our affection for this pearl of a natural satellite, a celestial object that holds a powerful sway over us mere humans.

In Native American cultures which tracked the calendar by the moons, December’s Full Moon was known as the Full Cold Moon, as it marked the time when winter begins its cold grip. In some tribes, it was called the Long Nights Moon, given the long nights and short days of December. Meanwhile, the Old English/Anglo-Saxon name is the Moon Before Yule

Sky mapping

On the solstice, sky-gazers will be able see the plump moon cozy up to the bright star Aldebaran. According to NASA, at 2:31 a.m. EST on December 21, the moon will share the same celestial longitude as Aldebaran, an occurrence known as a conjunction.

The full moon will be in the constellation Taurus and will rise about 15 minutes after sunset on the 22nd.

Santa's little helper

By Christmas Eve, the moon will still be glowing brightly with 96.7 percent illumination. Good news for people navigating rooftops looking for chimneys to slip into.

Waxing, waning

After she is full on the 22nd, the waning moon will diminish on her way to the last quarter moon of the year, which will occur on December 29 at 4:34 am EST.

Let the moon guide you

And this is where we take a hard swerve from science to note the best days for activities based on the moon’s sign and phase in December, according to the Farmer’s Almanac:

December 1, 3, 29, 30: Cut hair
December 5, 28: Quit Smoking
December 25, 26: Travel for pleasure

And some bonus magic

The full moon isn't the only star of the night sky, so to speak. Few things are as magical as the heavens full of shooting stars, and December gives us that gift in the form of the Ursid meteor shower. The Ursids begin around December 17 and perform their spectacular show until just after Christmas. They are named for the constellation Ursa Minor, DBA the Little Dipper, and appear to shoot out from it. One can usually see between 10 and 100 shooting stars per hour during this event. This year's peak happens on the 22nd, but the moon may brighten the sky too much to get the full effect, so look for them (best after midnight) in the days before and after.

Happy solstice and sky-gazing!

Everything to know about the spectacular winter solstice moon
How fitting that on the longest night of the year, the moon will be shining brightly.

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