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Winter solstice 2018: Full moon, meteor shower mark unusual 'shortest day of the year'

A full moon rises behind the Quaker Oats sign in Cedar Rapids on Thursday, Nov. 22, 2018. (Stephen Mally/The Gazette)
A full moon rises behind the Quaker Oats sign in Cedar Rapids on Thursday, Nov. 22, 2018. (Stephen Mally/The Gazette)
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Winter arrives Friday with the solstice at 4:23 p.m. — the moment at which Earth’s axis tilts the Northern Hemisphere farthest from the sun’s warmth.

Here are four things that make it a special one:

It (nearly) coincides with the Long Night’s Moon

December’s full moon, known as the Long Night’s Moon or the Cold Moon, falls just about on the “longest” night of the year. It arrives at 11:49 a.m. Saturday, so technically on the second day of winter.

But the moon will appear full both Friday and Saturday nights, and on both nights there will be about 14 hours, 53 minutes of darkness in the Cedar Rapids area. The sun will rise at 7:31 a.m. and set at 4:38 p.m. on both days, with just two fewer seconds of daylight on Friday — the “shortest” day of the year.

According to Space.com, the full moon hasn’t fallen on the solstice since 2010 and won’t again until 2094.

There’s also a meteor shower

By Friday, the Ursid meteor shower will be nearing its peak. The shower gets its name because its meteors appear to emanate from Ursa Minor, also known as the Little Dipper.

It’s not the best meteor shower of the year — as many as 10 meteors can be visible per hour, and the aforementioned full moon could outshine some of them — but it’s one more celestial event of interest.

Cloud cover shouldn’t be a big problem Friday night — it will be partly cloudy, according to the National Weather Service, with a low of 23 degrees.

You can spot a rare Mercury/Jupiter conjunction

Look in the southeast before sunrise Friday and see Mercury and Jupiter appearing as if they’re about to collide in space (don’t worry, they’re hundreds of millions of miles apart).

Mercury is the most difficult of the visible planets to spot, because as the innermost planet in the solar system, it never appears far from the sun. That doesn’t give much time to find it before sunrise.

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On Friday, Jupiter will appear right next to it, making it a little easier to find. Jupiter will be the brighter and larger of the two. Look about an hour before sunrise, in the 6 o’clock hour.

It will be longer than 24 hours

OK, this is actually the case for every winter solstice, but it’s nonetheless odd. At this time of year, each day is actually about 24 hours, 30 seconds long. (Each solar day, that is — the time it takes for the sun to reach its highest point in the sky from one day to the next. The 24-hour clock doesn’t change.)

As EarthSky.org explains: It’s because Earth is nearing its closest point to the sun in its elliptical orbit. That makes the planet move slightly faster than average through space, which means that it must rotate a little farther than average to reach its next solar noon.

When we talk about the length of the day at the solstice, though, we’re usually referring to the amount of time the sun spends above the horizon. That hits a nadir at nine hours, seven minutes in the Cedar Rapids area Friday — after which the days start getting “longer” again.

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