The month of December always marks the beginning of winter for us in the northern hemisphere. This year that will happen at exactly 4:12 a.m. on Dec, 21. That is called the winter solstice and marks the longest night and shortest day of the whole year as the sun reaches its lowest point in our sky. For us at this latitude of 43.5 degrees north, the sun will only reach 24 degrees into our sky at high noon. By comparison, it reaches 68 degrees high on the summer solstice. The word solstice means “sun stands still”.

The sun will rise at 7:12 a.m. and already set at 4 p.m. However, even though this is the shortest day, it is not the latest sunrise. That will occur about two weeks later and the earliest sunset of 3:59 p.m. happened on Dec. 8. That is because we orbit the sun in ellipses and not perfect circles and we are tilted at 23.5 degrees with respect to our ecliptic plane.

We had an unusually warm fall, but that is bound to change to closer to normal for our winter. All the seasons are great here in New England and each one has many unique features to offer. You just need to be prepared to be able to enjoy all of it. There are several great highlights this month to help you enjoy the sky above us and learn many useful new things about our true place in space and how everything is always moving through this inconceivably vast space that all of us inhabit.

Some of the many wonderful highlights that we will encounter this month that will make it well worth your while to brave any cold weather that mother nature may throw at us include Jupiter at its best, Venus getting higher and brighter in our evening sky and Mars beginning its retrograde motion on the same day that Jupiter reaches opposition, which is Dec. 7. Mars will reach its own opposition about a month after Jupiter, on Jan. 16, 2025. For part of this month all five of the brightest planets will be visible, but they will not be lined up in order like they were a few years ago in June in the morning sky. An asteroid named Eunomia will reach opposition at 8th magnitude near Jupiter on Dec. 14. The great comet of October, Tsuchinshan-ATLAS is still visible in Aquila the Eagle, but you will need a telescope to find it now. Then there is always the possibility of the BLAZE STAR, T Corona Borealis to erupt at any second and become 1,000 times brighter and easily visible to the naked eye at about the brightness of Polaris at 2.1 magnitude. Then there will be several nice conjunctions of planets with the moon and not one, but two meteor showers, the Geminids and the Ursids.

Jupiter, the king of our planets at 10 times the size of Earth will become the “star” of our evening sky this month. It will reach opposition on Dec. 7 which means that it will rise at sunset, remain in the sky all night long and not set until sunrise, similar to a full moon. That is also when any superior planet from Mars out to Neptune is at its closest and brightest for the year or the period when we are the closest to that planet, which is only once every 26 months in the case of Mars. Opposition always occurs at the midpoint of the retrograde loop of the superior planet. It just means that the planet is directly opposite the earth from the sun on that day.

This will be the best opposition of Jupiter in 10 years because it will be unusually high in the sky in Taurus this time as we get close to it this year. Look for Jupiter in the Winter Hexagon just to the left of the Pleiades open star cluster and just above and to the left of the orange star named Aldebaran, which is 65 light years away and marks the eye of an angry bull perpetually charging the might hunter Orion, but never able to get to him. The Pleiades star cluster consists of about 500 stars, only six of which are visible without binoculars and they form a shape similar to the Little Dipper, but only covering one degree of the sky instead of the roughly 10 degrees that the real Little Dipper covers as it is always dipping invisible liquid into the Big Dipper.

Mars will once again roughly double in brightness this month, from minus 0.5 magnitude to minus 1.2 magnitude. One full magnitude is 2.5 times difference in brightness and every 5 magnitudes is exactly 100 times difference. The red planet has now drifted into Cancer from Gemini and it will halt its relatively rapid eastward or direct motion against the fixed background of stars on the 7th, the same day that Jupiter reaches opposition. Then Mars begins its retrograde or westward motion back towards Gemini and it will reach its own opposition on Jan. 16, 2025.

It now rises at 8:30 p.m. and stands 30 degrees high outshining the nearby stars of the twins Castor and Pollux in Gemini and Procyon in Canis Minor, all part of the famous Winter Hexagon. Mars will pass near the Beehive Star cluster in Cancer when it appears to stand still for a day. This is a similar cluster to the Pleiades, but it has about 1,000 stars and is about 570 light years away. The light you will see from this other nearby cluster left there during a very important time which changed the course of history on Earth when the renaissance started at the end of the Middle Ages and the invention of the printing press by Gutenberg in 1440.

Venus continues to get brighter and higher in our evening sky as it is catching up with us in its faster orbit around the sun. Venus will enter Capricorn from Sagittarius on Dec. 6 as it also gets less illuminated by the sun. It will be only 55 percent illuminated and about 20% larger than it was when it started this month. It will reach a magnitude of minus 4.3 which makes it 15 times brighter than Mars and about four times brighter than Jupiter.

Saturn is still in Aquarius and is already up well before it gets dark. It is getting a little fainter each day as it is drifting farther and farther away from us. Through a telescope you will notice that its famous rings are getting quite thin. They will disappear completely from our line of sight in March of next year, but Saturn will sink below our horizon about then before it reappears in our morning sky.

The Geminids are usually the very best and reliable meteor shower each year, but this year they will peak just two days before the full moon on Dec. 14. So instead of 60 meteors per hour, you may only see about one tenth of that. This is one of only two of our 10 or so major meteor showers that is not directly caused by a comet. The Quadrantids on Jan. 4 is the other meteor shower caused by an asteroid and not a comet. The Geminids are caused by an asteroid named 3200 Phaethon which orbits the sun every year and a half.

They will all emanate from the radiant in Gemini and most of them will burn up about 60 to 70 miles high, which is where outer space starts at the Karman line where there are so few air molecules left that the sky will appear black in the middle of the day with a bright sun shining. They will tend to be brighter than other meteors because they are denser than regular comet dust. You will also see some greenish meteors caused by the oxygen, magnesium, and nickel in this asteroid.

The other meteor shower this month, the Ursids, will fare much better as far the phase of the moon goes, but it is a far less prolific shower with a maximum rate from a dark sky site of only six meteors each hour. The moon will be last quarter, so it will set around midnight, which is when meteor showers tend to get much better since the earth is then turning into the meteors instead of away from them like it does before midnight. The Ursids will peak on Dec. 22, the day after winter starts. They are caused by Comet 8P/Tuttle which orbits the sun every 13.5 years and they will all emanate from Ursa Minor, which is also commonly known as the Little Dipper.

DECEMBER HIGHLIGHTS

Dec. 1: New moon is at 1:21 a.m.

Dec. 4: The moon passes two degrees south of Venus this evening.

Dec. 7: Mars is stationary, ending its direct eastward motion and starting its retrograde motion today. Jupiter reaches opposition.

Dec. 8: The moon passes 0.3 degrees north of Saturn this morning. Neptune is stationary. First quarter moon is at 10:27 am.

Dec. 10: Mercury passes 7 degrees north of Antares in Scorpius this morning.

Dec. 13: The Geminid meteor shower peaks.

Dec. 15: Full moon is at 4:02 a.m. This is also known as the Cold, Long Night, or Moon before Yule.

Dec. 18: The moon passes 0.9 degrees north of Mars this morning.

Dec. 21: The winter solstice is at 4:21 a.m.

Dec. 22: Last quarter moon is at 5:18 p.m. The Ursid meteor shower peaks tonight.

Dec. 30: New moon is at 5:27 p.m.

Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.