Comet Leonard Leaps to Evening, the Moon Moves to Full, the Twins Shoot Stars, and Evening Planets Party!

This terrific image of Comet C/2021 A1 (Leonard) was captured by RASC member Paul Mortfield using RASC’s Robotic Telescope in the sierra Mountains of California on December 8, 2021 at 4 am PST. The green glow of the coma is apparent, and the ion tail points anti-sunward.

Hello, mid-December Stargazers!

Here are your Astronomy Skylights for the week of December 12th, 2021 by Chris Vaughan. Feel free to pass this along to your friends and send me your comments, questions, and suggested topics.You can also follow me on Twitter as @astrogeoguy! Unless otherwise noted, all times are expressed in Eastern Time. To subscribe to these emails please click this MailChimp link.

If you’d like me to bring my Digital Starlab portable inflatable planetarium to your school or other daytime or evening event, or teach a session online, contact me through AstroGeo.ca, and we’ll tour the Universe, or the Earth’s interior, together! My terrific new book with John A. Read entitled 110 Things to See With a Telescope is a guide to viewing the deep sky objects in the Messier List – for both beginners and seasoned astronomers. DM me to order a signed copy!

Comet Leonard hasn’t turned out to be all that bright. If you missed it in morning, it will switch to the post-sunset sky this week and pass Venus on Friday. Meanwhile, Venus will minimize its distance from Jupiter and Saturn while the bright moon waxes to the Full Oak Moon on Saturday night, and the year’s most prolific meteor shower peaks. Read on for your Skylights!

Meteor Shower News

The worldwide Geminids Meteor Shower, always one of the most spectacular of the year, runs from December 4 to 16 annually. The Geminids will ramp up to a peak number of meteors after midnight on Tuesday night, December 14, and then the shower will rapidly taper off during the following days. Keep an eye to the sky if you are outside on any clear night, or pre-dawn morning, this week.

Geminids meteors are often bright, intensely coloured, and slower moving than average because they are produced by sand-sized grains dropped by an asteroid designated 3200 Phaethon. You can watch for Geminids after the sky darkens on Monday evening until dawn on Tuesday morning. At about 2 am local time, more than 100 meteors per hour are possible under dark sky conditions. At that time the sky overhead will be driving into the densest part of the debris field. True Geminids will appear to radiate from a position above the bright stars Castor and Pollux, but the meteors can appear anywhere in the sky. A bright waxing gibbous moon shining on the peak night will reduce the number of fainter meteors in this year’s shower. But the moon will set at around 3 am local time, leaving us a few hours of prime viewing time.

To see the most meteors during any shower, find a safe, wide-open, dark location, preferably away from the city lights, and just look up with your unaided eyes for a good long while. Binoculars and telescopes are not useful for meteors – their field of view are too narrow. Try not to look at your phone’s bright screen because it’ll ruin your night vision. And keep your eyes heavenward, even while you are chatting with companions. Last December on Insider’s Guide to the Galaxy, we covered meteors and meteorites. It’s on YouTube here.

Comet Leonard Going Forward

For the past few weeks, I’ve been updating you about a comet named C/2021 A1 (Leonard) that was discovered by G. J. Leonard at the Mount Lemmon Observatory near Tuscon, AZ on January 3, 2021. After Comet Leonard’s orbit was calculated, astronomers were able to predict that it should brighten enough to see with unaided eyes this weekend. I wrote about comets in general last week here.

Comet Leonard was expected to be at its brightest and largest in the sky when it passed 35 million km from Earth (about one quarter of the Earth-sun distance) at perigee before dawn this morning, Sunday, December 12. Despite the hype, this comet has been a much less impressive sight than last year’s Comet NEOWISE. So, if clouds foiled your plans, don’t despair – you didn’t miss much.

Comet Leonard arrived from the northern (or top) side of the solar system. Over the next few days it will drop through the planets’ orbital plane while it also swings towards the sun. That means that the comet will be competing with the sun’s glare. On Sunday evening it will enter the western post-sunset sky, where it will sit less than a fist’s diameter above the western horizon at 5 pm in your local time zone. Be very careful to wait until the sun has fully set before using binoculars on the comet!

For the rest of this week, for observers at mid-northern latitudes around the globe, the comet will progress right to left (or celestial southeastward) above the western horizon after sunset. It will pass less than a palm’s width below (or 5° to the celestial southwest of) Venus on Friday. In space, comet Leonard will fly extremely close to Venus on December 17-18 – only 4 million km. That’s far closer than its minimum distance from Earth! To see the comet this week, you’ll need a cloud- and haze-free southwestern horizon. The best viewing time will be around 5:30 pm in your local time zone.

For viewers in the tropics and the Southern Hemisphere, this week will be the best for seeing the comet! Later in the week, it will climb higher and shine in a darkened sky in early evening – but every night it will be receding from Earth and diminishing in brightness and apparent size. That trend will continue after it passes the sun on January 3. I posted a 3D model of the comet’s trajectory through the inner solar system here.

A few more tips. The comet should resemble a faint fuzzy patch or unfocused star. Its fainter tail will point away from the sun. In binoculars or a telescope, look for a faint hint of green. If you use Stellarium or a mobile app, you should update the orbital elements for solar system objects so that the comet’s position is plotted correctly. Then use the app’s flip buttons to show the same orientation that your telescope produces and find the star patterns that should be surrounding the comet. If you still can’t see it, try tapping the telescope while you are looking. Making a faint fuzzy object “dance” a little will make it more visible.

I wish you clear skies and good luck! Let me know if you see it, or photograph it. And feel free to tag me on social media if you post about it.

The Moon

The moon will dominate the evening sky worldwide this week as it waxes from first quarter to full moon on the coming weekend. As the moon fills with light, the views of it through binoculars and backyard telescopes will be spectacular. Moreover, because of the early sunsets, even the youngest junior astronomers can enjoy its sights before bedtime!

Today (Sunday) the half-illuminated moon will cross the sky all afternoon. After dusk, the modest stars of Cetus (the Whale) and Pisces (the Fishes) will appear below and above it, respectively. Pegasus (the Flying Horse) will be flying directly over the moon, too – above the fishes. On Sunday evening, the terminator that divides the lit and dark hemispheres of the moon, will fall just to the left (or lunar west) of Rupes Recta, also known as the Lunar Straight Wall. The rupes, Latin for “cliff”, is a north-south aligned fault scarp that extends for 110 km across the southeastern part of Mare Nubium. That’s the dark patch sitting in the lower third of the moon’s Earth-facing hemisphere. The wall, which is very easy to see in good binoculars and backyard telescopes, is located above the very bright crater Tycho.

From Monday through Wednesday, the waxing gibbous (i.e., more than half-illuminated) moon will slide eastward, leaving the aquatic constellations and then dodging the hoofs of Aries (the Ram). On Tuesday, the bright moon will shine several finger widths to the right (or 4.5° to the celestial southwest) of magnitude 5.7 planet Uranus.

As darkness falls on Thursday, look in the eastern sky for the bright gibbous moon shining among the stars of Taurus (the Bull). The bright open star cluster known as the Pleiades and Messier 45 will be positioned within a binoculars’ field of view above (celestial north of) the moon. Scan your binoculars below (south of) the moon to see the bright star Aldebaran at the corner of the V-shaped stars that form the face of the bull. Those stars, known as the Hyades Cluster and Caldwell 41, are one of the closest open star clusters to Earth.

The moon will remain within the stars of Taurus until Saturday night. The December full moon will occur at 04:35 Greenwich Mean Time next Sunday, which converts to 11:35 pm EST on Saturday evening. The December full moon, colloquially known as the Oak Moon, Cold Moon, and Long Nights Moon, always shines in or near the stars of Gemini (the Twins). Since it’s opposite the sun on this day of the lunar month, the moon becomes fully illuminated, and rises at sunset and sets at sunrise. Full moons during the winter months at mid-northern latitudes reach as high in the midnight sky as the summer noonday sun, and cast similar shadows.

Indigenous groups have their own names for the full moons, which marked time and lit the way of hunters and travelers at night before modern conveniences like flashlights. Unlike our regulated western calendar, they linked the full moon to what is happening in the environment around them.

The Ojibwe of the Great Lakes region call the December full moon Manidoo Giizisoons, the “Little Spirit Moon”. For them it is a time of purification and of healing of all Creation. Their January moon is Gichi-Manidoo Giizis, the “Great Spirits Moon”. It is manifested through the northern lights, and is a time to honour the silence and realize one’s place within all of Great Mystery’s creatures. The Woodland Cree of the Central Canada call the December moon Thithikopiwipisim, the “Hoar Frost Moon”, when frost sticks to leaves and other things outside.

The bright moon will have waned a little when it rises around sunset next Sunday. By then it will have slide east into Gemini (the Twins). The prominent crater Copernicus is located in eastern Oceanus Procellarum – due south of big Mare Imbrium and slightly northwest of the moon’s centre. Copernicus’ 800 million year old impact scar is visible with unaided eyes and binoculars – but telescope views will reveal many more interesting aspects of lunar geology. Several nights before the moon reaches its full phase, Copernicus exhibits heavily terraced edges (due to slumping), an extensive ejecta blanket outside the crater rim, a complex central peak, and both smooth and rough terrain on the crater’s floor. Around full moon, Copernicus’ ray system, extending 800 km in all directions, becomes prominent. Use high magnification to look around Copernicus for small craters with bright floors and black haloes – impacts through Copernicus’ white ejecta that excavated dark Oceanus Procellarum basalt and even deeper highlands anorthosite.

The terms “maria” (the dark regions) and “terra” (the heavily cratered bright regions) were coined by Galileo Galilei after he began to view the moon in his little telescope around 1610. The rest of the moon’s naming system was developed by Jesuit priest Giovanni Riccioli. In 1651 he published a labeled moon map that all later maps derive from. He used the names of living and dead scientists and philosophers for the craters, assigning ancient notables to the north of the moon and “modern” (to him, anyway) personages in the south. He placed teachers and their famous students together.

The maria are all named for weather and states of mind, except for Mare Humboldtianum and Mare Smythii, who were famous explorers, and Mare Cognitum and Mare Moscoviense, discovered later on the moon’s far side. Fittingly, Riccioli placed the radical proponents of the heliocentric theory, Copernicus, Aristarchus, and Kepler in the Sea of Storms – and he honoured fellow Jesuits Grimaldi and Clavius with prominent craters.

The Planets

The three bright planets that have been shining in the southwestern sky after sunset for many weeks will achieve their minimum separation from one another on Tuesday night. Extremely bright Venus is positioned about three fist diameters to the lower right (or 31.5° to the celestial west) of bright Jupiter – with fainter Saturn midway between them. Venus’ eastward orbital motion with respect to the background stars, and towards Saturn and Jupiter, will continue until Tuesday. Meanwhile, those two gas giant planets are being carried west and sunward by Earth’s orbital motion. After Tuesday, Venus will shift towards the sun faster than Saturn and Jupiter, so their separation will widen. Venus will cease to be visible late this month, with the others to follow her soon afterward.

For now, brilliant Venus is shining low in the southwestern sky after sunset, and setting shortly after 7 pm local time. You might need to walk around to find a view of the planet between the trees or buildings after sunset. Viewed in a telescope, Venus will show a thin, waning crescent on its sun-facing side. Aim your telescope at Venus as soon as you can spot the planet in the sky (but ensure that the sun has completely disappeared first). That way, the planet will be higher and shining through less distorting atmosphere – giving you a clearer view of it. A brighter sky will also allow Venus’ shape to be seen more readily. The planet will grow in size and wane in phase every week for the rest of this year because Venus will be traveling into the space between Earth and the sun.

Jupiter and Saturn, parked at the opposite ends of the constellation of Capricornus (the Sea-Goat), will become visible a short time after dusk. Look for them shining less than a third of the way up the south-southwestern sky. You’ll need the sky to darken a little more before 18 times fainter Saturn appears, 1.5 fist diameters to Jupiter’s right (or 15.5° to the celestial west). Jupiter and Saturn will set in the west, 90 minutes apart, after mid-evening – so observe each planet as early as you can spot it, while it’s higher. Don’t miss your chance – they’ll become unobservable in telescopes within a few weeks!

Saturn and its beautiful rings are visible in any size of telescope. If your optics are sharp and the air is steady, try to see the Cassini Division, a narrow gap between the outer and inner rings, and a faint belt of dark clouds encircling the planet. Remember to take long, lingering looks through the eyepiece – so that you can catch moments of perfect atmospheric clarity.

From here on Earth, Saturn’s axial tilt of 26.7° lets us see the top of its ring plane, and allows its brighter moons to array themselves all around the planet. Saturn’s largest and brightest moon Titan never wanders more than five times the width of Saturn’s rings from the planet. The much fainter moon named Iapetus can stray up to twelve times the ring width during its 80-day orbit of Saturn. The next brightest moons Rhea, Dione, Tethys, Enceladus, and Mimas all stay within one ring-width of Saturn.

During this week, Titan will migrate counter-clockwise around Saturn, moving from the left (celestial east) of Saturn tonight to the lower right (celestial west) of Saturn next Sunday. (Remember that your telescope will probably flip the view around.) How many of the moons can you see in your telescope?

Binoculars and small telescopes will show you the Jupiter’s four large Galilean moons named Io, Europa, Ganymede, and Callisto. Since Jupiter’s axial tilt is a miniscule 3°, those moons always look like beads strung on a line that passes through the planet, and parallel to Jupiter’s dark equatorial belts. That line of moons, and the belts, tilt as Jupiter crosses the sky. The moons’ arrangement varies from night to night. Io, for example, orbits Jupiter once every 42 hours. From one night to the next night, 24 hours has elapsed on Earth – time for Io to complete half an orbit and shift from one side of Jupiter to the other. The other Galilean moons move less rapidly, taking between 3.5 and 16.7 days to orbit Jupiter.

For observers in the Eastern Time Zone with good telescopes, the Great Red Spot (or GRS) will be visible while it crosses Jupiter after dusk on Monday, Wednesday, and Saturday, and after mid-evening tonight (Sunday), Friday (with Europa’s shadow), and next Sunday.

From time to time, the small, round, black shadows cast by Jupiter’s Galilean moons become visible in amateur telescopes when they cross (or transit) the planet’s disk. On Friday evening, December 17, observers in the Americas with telescopes can watch the small round shadow of Jupiter’s moon Europa cross the planet accompanied by the Great Red Spot. The spot will begin to cross at about 6:35 pm EST. The shadow of Europa will join it after 7:55 pm EST (or 23:55 GMT). Jupiter will be setting in the Eastern Time Zone before they complete their crossing, but observers farther west can watch them  longer.

Distant, dim Neptune is in the evening sky, too – near the border between Aquarius (the Water-Bearer) and western Pisces (the Fishes). The magnitude 7.9 planet is also 2.3 fist diameters to the upper left (or 23° to the celestial east) of Jupiter. Uranus is shining at magnitude 5.7. Look for the planet’s small, blue-green dot moving slowly retrograde westwards in southern Aries (the Ram), a fist’s width below (or 11.5 degrees southeast of) that constellation’s brightest stars, Hamal and Sheratan. Or use binoculars to locate Uranus using the nearby star Mu Ceti. Uranus is also about 1.6 fist diameters to the upper right (or 16 degrees to the celestial west-southwest) of the Pleiades star cluster. This week Uranus will be observable all night long – especially around 9:30 pm local time, when it will have climbed more than halfway up the southeastern sky. But the bright moon will spoil our views of both of the ice giant planets.

This week Mars will continue its year-long journey to a bright showing at opposition in December, 2022. You might spot the magnitude 1.6 planet shining very low in the east-southeastern sky just after it rises at around 6 am local time, especially if you live at a tropical latitude. Your odds of successfully spotting Mars will improve on each subsequent morning. Take care to turn binoculars and telescopes away from the eastern horizon well before the sun rises.

Mercury will become observable in the western post-sunset sky next week.

Public Astro-Themed Events

Every Monday evening, York University’s Allan I. Carswell Observatory runs an online star party – broadcasting views from four telescopes/cameras, answering viewer questions, and taking requests! Details are here. Their in-person Wednesday night viewing has been converted to online via the observatory YouTube channel.

On Tuesday night, December 14 from 8 to 9 pm EDT, SkyNews Magazine editor Allendria Brunjes and Canadian astrophotographer Paul Owen will host Subs and Stars – Lesson 4 of a free, eight-part online series on astrophotography. This session will cover advanced image stacking and processing. Details are here, and the registration link is here.

RASC’s in-person sessions at the David Dunlap Observatory may not be running at the moment, but they are pleased to offer some virtual experiences instead, in partnership with Richmond Hill. The modest fee supports RASC’s education and public outreach efforts at DDO. On Friday night, December 17 from 7 to 8:30 pm EST, tune in for Up in the Sky. During the family-friendly session, RASC astronomers will live-stream views through their telescopes and the giant 74” telescope at DDO (pre-recorded views will be used if skies are cloudy). Only one registration per household is required. Deadline to register for this program is Wed., December 15, 2021 at 3 pm. Prior to the start of the program, registrants will be emailed the virtual program links. The registration link is here.

My free, family-friendly Insider’s Guide to the Galaxy webcasts with Jenna Hinds and Samantha Jewett of RASC National returns on Tuesday, January 18 at 3:30 pm EST. You can find more details and the schedule of future sessions here.

Don’t forget to take advantage of the astronomy-themed YouTube videos posted by RASC Toronto Centre and RASC Canada.

Keep looking up, and enjoy the sky when you do. I love questions and requests. Send me some!