Boy, does it get dark early now. The December Solstice (i.e., the Winter Solstice here in the Northern Hemisphere) is less than three weeks away, and the sun is nearing its most southerly station for the year. The exact day of the solstice will be the 21st, but the sun moves very slowly near the solstices and it is already close to its limit, where it will stay for a while as it slowly turns around before heading back north again. Here in the Northern Plains, I'm looking forward to 4 PM sunsets and 8 AM sunrises for the next month and a half. Welcome to winter!
Two Special Local Events
Before I get to more "normal" stuff, I want to mention a couple of events that you will probably not be able to see, but that could be very dramatic if you can.
As you may already be aware, there is a total solar eclipse happening very soon (tonight, actually), but it will only be visible near the South Pole. You will only be able to see totality if you live in Antarctica. However, if you live near Cape Horn, the Cape of Good Hope, or Tasmania, you may get to see a very brief and very partial solar eclipse. I'm pretty sure that this does not include anyone on this mailing list, but if it does, I apologize for that late notice. If you're interested in more details, I recommend Time and Date.
Second: On New Year's Eve 2021, the Moon will collide with Mars. Or rather, it will pass in front of Mars and block it from view temporarily. As you are no doubt aware, the moon wanders gradually through the constellations, making a complete circuit of the zodiac once a month, and sometimes it passes in front of stars or planets. It doesn't do this as often as you might think, however, and these "occultations" can be hard to observe when they do. For one thing, if the moon is full and the star is dim, the contrast will be too great, and you won't be able to see the star next to the moon anyway. It's a more interesting event when the moon is a thinner crescent, and it passes in front of a brighter planet. This is what will happen later this month.
Another problem with lunar occultations is that, like solar eclipses, only a small part of the world gets to see each one. This also is what will happen later this month.
As the old year becomes the new year, on the night of December 31st, there will be a lunar occultation of Mars, but it will be visible only to residents of Southern Australia. One of my reputable web sources said the event would last around half an hour, and would begin around 6 PM local time, but I'm reasonably certain he meant 6 AM. This site has a nice map of where the occultation will be visible, and this web page has some technical details about the event, including a list of Australian cities in which it will be visible, with times of occurrence (in Universal Time).
The sunsets continue to be lovely this month, with the two brightest planets (Jupiter and Venus) both very prominent in the evening skies. Saturn currently lies about halfway in between the two of them, providing a very nice, evenly spaced triplet in the evening skies. Seldom do you have such a beautiful marker of the zodiac, or the "solar system in the sky". What else lies on the same line? What happens if you extend the line in your imagination towards, and then below, the western horizon, where the sun just set? Today, the 3rd, is also the day of December's new moon. (This is also, not coincidentally, the day of the solar eclipse.) What happens to the moon after it becomes "new"? What is going to join the evening scene in a few days, and then march westward along the "planet highway" across the sky?
All three of the evening planets will sink lower towards the sunset as the month progresses, and Venus will disappear from view shortly after the New Year. On the other hand, Mercury will be moving in the opposite direction, rising over the sunsets, and will become visible in late December. When it does, you will have a chance to see four of the five visible planets together over the sunset. (To see the fifth visible planet, Mars, you have to get up before the sun and look very low over the sunrise.)
By the way, I usually make my images of the sky, including the one above, for the latitude of Central Iowa, i.e. 42 or 43 degrees North. This is where I live, and residents of the United States all live near or somewhat south of this latitude, while most residents of Europe live somewhat north of this latitude.
If you live in the Southern Hemisphere, you will also have beautiful sunsets for the next month, with the same planets, but the planet lineup will be tilted into the northern sky instead of the southern. The trio of planets will rise from the western horizon along a diagonal tilted to the right instead of the left. The zodiac or "planet highway" runs across your northern sky instead of your southern sky.
The Geminid Meteor Shower
Coming up in mid-December, we will also have one of the better meteor showers of the year: The Geminids. It is hard to define "average rates" for meteor showers, but the rates for the Geminids are considerably higher than most other showers. If you are lucky, have good eyesight, and dark skies, on the night of the peak you might be able to see over 100 in an hour. The peak will be the morning of the 14th, but you may see substantial rates for a day or two on either side of the peak as well. Officially, the Geminids will actually be "active" for a couple of weeks, from the 4th to the 17th.
The only drawback this year is that the moon will be about 77% illuminated on the night of the peak — not completely full, but still very bright. This will drown out the dimmer meteors and reduce the number that you can see. On the other hand, on the night of the peak, the moon will set around 3:30 or 4 AM, and the pre-dawn hours are often the best for meteor showers anyway. So if you just plan to get up extra early, say 4 AM, on the 14th, you might be in for a treat. As always, find a dark place with a wide view of the sky, let your eyes adjust to the dark, and just enjoy the sky for ten minutes or an hour.
This meteor shower can be enjoyed all around the world, but it does favor the Northern Hemisphere slightly.
In addition to the Geminids, we will also have the Ursids on the 20th, but that is a pretty weak shower, and that one is only visible in the Northern Hemisphere.
Sometimes we find an object in the night sky that doesn't belong. Or rather it doesn't belong to a specific place on the map, because it moves. If it shoots across the sky in a second or two and then disappears, we call it a meteor. In contrast, sometimes we find a dim, hazy, solitary trespasser that wanders slowly through the constellations for several weeks, gradually growing brighter, and then gradually fading back to nothing again after an extended stay in our skies. On rare occasions, these fuzzy smudges grow a long tail. This tail always points away from the sun, for some reason, like hair flowing in wind from the sun. These lone wanderers with a long mane we call "comets", from a Greek word for "hair".
Most comets are only interesting to professional astronomers. They are faint, tailless, visible only in powerful telescopes, and very unspectacular, like insignificant smudges on the sky. But very rarely, a special comet will come along that impresses the world. It grows a long glowing tail, and it shines so brightly that you can see it clearly in the night sky without equipment.
And then there are the comets that fall somewhere in between the extremes. Comet Leonard is a recently-discovered comet that is in this middle ground. It probably won't be spectacular, but if you can find it, it should make a pretty sight in binoculars or small telescopes. It may even grow a tail and become weakly visible to the naked eye, but that is hard to predict. (Like meteors, the appearance of comets depends on many factors, many of which are unknown.)
But finding comets in the sky, even medium comets like Leonard, often requires you to hunt. Even the bright ones are "diffuse", or smeared out, making them harder to recognize, and they move quickly through the constellations, never staying in the same place two nights in a row. Casual stargazers with binoculars will probably need star charts to know where to look, and I'm having a hard time finding those. This website gives lots of unhelpful technical data, but there are also a few finder charts that amateurs might find useful. This site also gives some helpful hunting advice. The free software Stellarium can create wonderful, exact maps for any location and for any date and time, but you need to configure it to include Comet Leonard. Email me privately if you'd like some help setting up Stellarium.
In a nutshell, use your binoculars to hunt above the sunrise until the 12th, and hunt low over the sunset starting on the 14th. To be just a little more precise (and assuming you live in the Northern Hemisphere): Over the sunrise, imagine a vertical line coming up from the eastern horizon, standing just slightly to the left of the bright orange star Arcturus. Leonard is currently a little above Arcturus, and it will descend almost directly downward until it meets the horizon on about the 12th. On around the 14th, start hunting in the evening skies close to the horizon, below Venus. The comet will move in a low arc below the planet triplet, appearing under Venus around the 14th, and disappearing finally under Jupiter around the 24th or 25th or so. But it will be very low the entire time, and I worry that it might be hard to find in the horizon haze. In the coming days, there will be a trade-off between brightness and altitude above the horizon, and I think your best bet to see it might be in the morning skies in about a week.
That's all for now. Good luck, and Happy Hunting!