Astro Bob: Celestial sights at the solstice
Happy first day of winter! The sun did the limbo today, dipping as low as it could go. Plus, I have an update on Comet Leonard's eruption and a map to find it.
At 9:59 a.m. CST Tuesday morning (Dec. 21) the sun finally bottomed out in the sky, six months after it began its southward journey on the summer solstice. The start of winter lasted only a moment. Before the clock read 9:59:01, the sun had already turned the corner and was heading north again. Nothing stands still in the cosmos. Earth's motion around the sun is the cause of the sun's apparent motion in the sky. As long as the planet skedaddles along its orbit, the sun continuously slides east across the sky.
If the Earth's axis were straight up and down instead of tilted at a 23.5° angle, the sun would rise due east, set due west and pass due south at the same altitude every day of the year. There would be just one season — spring, or if you like, fall. But the tilt of Earth's axis over the course of its orbit "plays" the sun, causing it to move north and south in the sky. And that's precisely why we have four seasons instead of one.
While the solstice is instantaneous, winter is not. In northern Minnesota, it's been here for a month already and has plans to stay until at least March. Waking up to four inches of fresh snow this morning was a further reminder of the new season. Give it to me! I'm ready for Orion, Gemini and full moons that light up the night like day.
What I'm not ready for is seeing Venus depart its fellow bright planets Jupiter and Saturn in the southwestern sky at dusk. The trio has been hanging out together for months. Sadly, we're in the middle of a long goodbye as Venus prepares to shove off for the morning sky on January 8. That's when it will pass directly between the Earth and sun in inferior conjunction. For a couple weeks centered on that date, we'll lose sight of it in the solar glare. The three familiar dusk "stars" will dwindle to two.
Not so fast! Attempting to fill those big Venusian shoes, Mercury briefly comes to the rescue for a little more than two weeks starting around Dec. 28. Watch for it to pop up below and to the left of Venus in the final days of 2021. Venus disappears in the twilight glow around Jan. 2 but will reappear in the eastern sky at dawn around the 20th. Since this planetary hopscotch happens around the New Year, Venus serves as a delightful metaphor of transition and change, topics topmost on minds of many as the old year gives way to the new. Follow your inner star.
Comet Leonard has been a big topic on the Internet this past week, with lots of hyperventilating about how bright it's become after a recent explosion. Well, it's definitely brighter. When the comet arrived in the evening sky a week ago, it wasn't particularly obvious. But a recent disruption in the icy heart of the comet called nucleus on Dec. 19 vaulted its brightness to around magnitude 2.5-3. Suddenly, it was possible to see it from places like Minnesota.
Just one little problem. Altitude. By the time the sky gets reasonably dark (about one hour to 75 minutes after sunset), the comet is so low (between 3-5°) that it's virtually impossible to see unless you know exactly where to look. Even then, Leonard looks like a faint puffball in binoculars. I know because I went out under very clear skies last night, and although I found and photographed Leonard, it was faint. The view in the telescope was better, with the comet showing a bright, glowing core and short tail pointing east-southeast.
Its brightness at the time was about magnitude 3. If it were higher up in a dark sky, as it is in the southern U.S. and particularly in southern hemisphere, we'd see it without optical aid. I'm including a map here to help you find it. I used the bright planets and the two labeled stars in the bottom of Capricornus to guide me to the location. I first spotted this faint fuzzy by taking pictures and studying the back viewfinder on the camera. Once I knew where to look, I could point my binoculars to the spot and see it. But again, not easy!
Comet Leonard will gradually pull away from the sun in the next few weeks but remain stubbornly low for observers in the northern half of the U.S. I hope you find it just the same — good luck!
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob .