Champaign-Urbana Astronomical Society
Looking Up This Month We have three major events in December, two of which will be visible . . . .well, provided it’s clear; and the third you might watch online. We begin with the Geminid Meteor Shower. If it’s clear, we have the perfect conditions this year. The shower occurs on a weekend and the Moon is new on the following Monday, producing dark skies. The Geminids are just as potent as the August Perseids but usually don’t get the press due to the clouds and cold of a typical December. Start looking Saturday maybe 9pm and see how long you can stay out. Numbers typically increase after midnight and, though meteors sometimes appear in groups, they average two a minute. Recall meteors occur when pea-sized dust hits our atmosphere at 80,000 miles per hour and, in slowing down, their kinetic energy is transferred to the air, causing it to glow. Geminid meteors will appear to come from the northeast, but just look upwards and obviously dress as warm as you can. On Monday morning, the 24th, we have the new Moon. And it just so happens that, this time around the Earth, the Moon will pass in front of the Sun and we have a total solar eclipse. We won’t see this from our backyards as the Moon’s shadow goes from west to east in the south Pacific ocean, crossing South America at Chile and Argentina. Totality is just over two minutes long. You can watch the event on livestream (can’t you see about anything on livestream anymore?) by going to the San Francisco Exploratorium site (www.exploratorium.edu/ eclipse). I believe coverage starts at about 8:30am. Hopefully you have been keeping track of Jupiter and Saturn as they close in on each other. They will be the two brightest star-like objects in the southwest right after sunset. They start the month about two degrees apart. On the 16th, a thin crescent Moon should be visible below the pair of planets. The long-awaited grand conjunction occurs on the evening of Monday, the 21st. The planets will be a tenth of a degree apart and you should be able to see them (and their moons) in the same low power telescope field of view. Saturn is 1.8 times farther away than Jupiter. This conjunction occurs every 20 years and was one of the sky events that greatly interested Johannes Kepler which lead to his laws of planetary motion. The magazines report the last time these two planets were this close was 400 years ago, but that approach wasn’t visible. The last visible gathering occurred in March of 1226 CE!! Though there isn’t an official observing session due to the virus, the observatory (with its low horizon) would be a nice place to check out the event. Again, look quickly as the pair will be 14 degrees high and will set soon after 6:30pm. Mars is rapidly fading and shrinking though still showing some surface features this month. It’s still bright at magnitude -0.7 and, being in the star-poor region of Pisces, it’s easy to pick out. A waxing gibbous Moon is just below Mars on the evening of the 23rd . Shifting to the morning sky, Venus rises at roughly 5:15am as it glides through Libra. On the morning of the 12th a thin crescent Moon is just above this brilliant planet. On the morning of the 26th, Venus rises to the left of the red star Antares. Mercury is briefly visible early in the month (though quite low) and it passes behind the Sun on the 19th . Late-breaking news . . . .Comet Erasmus (C/2020 S3) was discovered this past September 17th by an amateur skywatcher in South Africa. As this issue goes to press, the comet has brightened from 7th magnitude to possibly 5th magnitude. Perihelion is December 12. The comet is in the morning sky, in the southeast, to the right of Venus. Let us know if you see something! -DCL
Did you get a good look at Mars last month? Hope so! This month the Earth speeds away from all the visible outer planets. Mars, Jupiter and Saturn will all dim and shrink in apparent diameter. Jupiter and Saturn are in the south at sunset and they are creeping closer to each other. This month they’ll go from 5 degrees down to 2.3 degrees. The big conjunction (a once every 20 year event) is next month.
Jupiter sets at 10:30pm CDT at the beginning of the month and then 8pm CST by the end of November. A beautiful crescent Moon makes a nice triangle with these two planets on the evening of the 19th (pictured here). Of course the four Galilean moons of Jupiter and the rings of
Saturn still impress. The rings are tilted at a nice 22 degree angle. Mars will still draw the attention of telescopes this month, even though closest approach occurred last month. The planet dims from magnitude –2.1 to -1.2 and shrinks from 20.1 to 14.8 arc seconds. Still large enough to see a few surface features.
Better yet, wait until 9-10pm when Mars is highest in the sky so you’re looking through less terrestrial air. Sky & Telescope magazine has a nice site that will show you which side of Mars you’re seeing. Check it out at: https://is.gd/marsprofiler. A waxing gibbous Moon is just below Mars on the evening of the 25th.
The rest of the action is in the morning sky where Mercury joins Venus. Venus rises not quite three hours before the Sun in early November to 2 ¼ hours at the end of the month. Venus is inside the constellation boundary of Virgo. Mercury joins Venus early in the month in what could be argued as its best morning view of the year. Mercury rises rapidly and reaches greatest separation from the Sun on November 10th (20 degrees). But look early in the month and catch Mercury just to the left of the star Spica. Mercury rises about an hour after Venus and shines at magnitude +1.6, but it will brighten to -0.6. It almost seems like these two planets are destined to meet each other as Mercury gets higher and Venus gradually gets lower, but Mercury makes the big turn-around November 7th and heads back towards the Sun. It’ll be tough to see by the end of the month. Venus will also pass Spica on the morning of the 17th. Look east-southeast.
A very thin waning crescent Moon will rise between the planets on the morning of the 13th (pictured here at 6am) We’ll have a penumbral lunar eclipse on November 30th beginning 1:32am CST. Remember this is a “penumbral” eclipse, meaning the Moon goes through the lighter part of the Earth’s shadow. There is a lighter part of the shadow and a darker part, all due to the fact the light source (Sun) is not a point source. So the Moon won’t go dark but you may see a faint shading of the lunar surface. Mid-eclipse occurs at 3:43am when 83% of the Sun is within the penumbral shadow. The event is over by 5:53am. This is the fourth penumbral lunar eclipse in a row.
The Leonid Meteor Shower peaks on the morning of November 17th. No outburst is expected (in face the predicted hourly rate is 10-15 meteors per hour) but you never know. Though not the most potent shower of the year, the Moon is in a good spot leaving some dark skies for observation. Meteors are the dust shed by Comet Tempel-Tuttle.