December sky

We’re coming to the last month of the year, with the winter solstice, Christmas, snowy weather, and dark nights. Alas, in our part of the world most of those dark nights are also cloudy. Step outside when it is clear and enjoy the celestial sights!

Winter solstice comes on December 21, when the Sun will be at its lowest point in our sky, and we have our shortest day. The Sun will only be about 20 degrees above the southern horizon at its highest. We’ll have only about 8 hours and 38 minutes with the Sun above the horizon. If that depresses you, remember days will start getting longer. By New Year’s Day, we’ll have picked up about 5 minutes of daylength already.

There was much activity in November with people watching for a display of Aurora Borealis, the Northern Lights. We didn’t get much of a display, but hopefully will get more chances in the future. Solar activity, which is responsible for phenomena like aurorae or sunspots, runs on a roughly 11-year cycle. Activity was lowest in 2019 and should be at maximum between 2023 and 2026. Aurorae occur when strong activity on our Sun releases ionized particles, a “Coronal Mass Ejection.” If the ejection is toward Earth, those ionized particles reach us in a couple of days. They are deflected by Earth’s magnetic field, but some make it into our atmosphere, especially where the magnetic field is weaker, near the poles. The particles collide with atoms in our atmosphere, and the collisions emit the colors we see. Red can result from collision with oxygen atoms high in our atmosphere, and yellow-to-green light at lower elevations. Nitrogen at lower elevations may also produce red color, often on the fringes of the aurora. Cameras can capture more of the light than our eyes, so often the pictures you see are more vivid than what you may have seen with your naked eye.

The farther north you are, the better chance you have of seeing the Aurora. They are relatively rare at our latitude, visible only when we have strong solar storms.

When to look? There is no magic, alas. A good website is the Space Weather Prediction Center’s Aurora forecast, at www.swpc.noaa.gov/products/aurora-30-minute-forecast. If you are on Facebook, there now is an “aurora borealis Washington State” group that has sighting reports, and great information about the phenomenon.

The bright planets Venus, Jupiter, and Saturn are still hanging in our evening sky. Late in the month, they’ll be joined (right after sunset) but little Mercury, very low in the southwest. On Christmas Eve, Mercury, Venus, Jupiter, and Saturn will be lined up in the evening sky, at 5 p.m. By New Year’s Eve, Mercury will be a bit higher in the sky, just to the left of bright Venus.

December’s full Moon will occur on the 18th. New Moon will be on the 3rd of December. The Moon will be just below Saturn on the 7th, and near Jupiter on the 8th and 9th. The nearly full Moon will be below the Pleiades star cluster on the 16th. The red planet Mars is now low in our morning sky, low in the southeast at sunrise.

The Geminid meteor shower peaks on December 13-14. The waxing gibbous Moon will “wash out” some of the meteors. Best chance for viewing is probably in the early morning hours of December 14, while the sky is still dark before sunrise. The Moon sets at about 4:30 a.m., so about that time might be a good time to take a look.

We have a comet to look for in December as well. Comet Leonard may be visible close to the horizon, on the morning of December 12 (low in the East), or in the evening of Dec. 14 and a few days later, very low in the west, near bright Venus. Leonard may be visible to the naked eye, but most likely a pair of binoculars will be necessary.

Enjoy December’s skies, and Happy Holidays to all!