This Week’s Sky at a Glance, December 10 – 18


Comet Leonard (C/2021 A1) is correct now at its greatest! It’s about magnitude 5.5, low due east tomorrow morning the eleventh. Go out simply earlier than the very first gentle of daybreak, which means about 90 or 100 minutes earlier than your dawn time. The comet might be about 10° above horizontal.

You’ll virtually definitely want binoculars or a wide-field telescope to detect it. Use the finder chart at the underside of See Comet Leonard at its Best that can assist you find the precise place among the many stars you should look at.

On Sunday morning the twelfth Comet Leonard could also be simply a hint brighter, however it’ll be a lot decrease and extra concerned in morning twilight.

Later this week the comet will reappear very low within the west throughout night twilight; see December sixteenth beneath. But by then it is going to be fading. For the world’s mid-northern latitudes, tomorrow morning is your final likelihood to catch it at peak brightness in a darkish sky.

■ First-quarter Moon tonight (precisely so at 8:36 p.m. EST). At nightfall the Moon shines far off the upper-left finish of the Venus-Saturn-Jupiter line, turning it into an immense, gently curving sequence of 4 objects.

■ Algol, excessive overhead in Perseus after darkish, needs to be at minimal gentle (magnitude 3.4 as a substitute of its ordinary 2.1) for a couple hours centered on its mid-eclipse time of 8:27 p.m. EST.


■ Venus and Jupiter proceed to blaze throughout and after twilight within the southwest and south-southwest, respectively. As twilight fades, dimmer Saturn emerges between them.

Jupiter and Saturn are far previous opposition, so do not be disenchanted by the less-than-optimal telescopic views. Venus, alternatively, is enlarging whereas turning into a thinner, extra dramatic crescent. It will proceed to take action into the start of January.

■ Not that you simply’d have any attainable way to see it, however this night Pluto is lower than 1° from Venus, 100 occasions farther within the background. And it is a lot farther from the illuminating Sun in addition to from us. All which means Pluto, at magnitude 14.4, is 50 million occasions fainter that Venus!

■ Have you seen any early Geminid meteors but? The bathe is because of peak in two days, late on the evening of December 13-14. See Bob King’s Precious Hours with the Geminids.


■ Orion strides up away from the east-northeast horizon by 7 p.m. now. By 9 or 10 he shows himself excessive within the southeast in full wintry glory.

■ The Big Dipper lies shyly down at its lowest simply after darkish, due north. It’s fully beneath the north horizon should you’re as far south as Miami.

But by 11 or midnight the Dipper stands straight up on its deal with in effective view within the northeast. By that point Cassiopeia has wheeled over to the excessive northwest and stands practically upright on the brilliant finish of its W form.


■ The Geminid meteor bathe, usually the most effective of the year, needs to be at its peak late tonight. The gentle of the waxing gibbous Moon will wash out faintest meteors till the Moon units round 3 a.m. By then the bathe might be in full drive, with its radiant excessive overhead. You have about three wonderful dark-sky hours between then and the primary gentle of daybreak. Under a actually darkish sky throughout that point, you would possibly see two or three meteors per minute on common. Under suburban gentle air pollution, possibly extra like one a minute.

In early night the meteors might be fewer as a result of the bathe’s radiant level (in Gemini) might be low. But people who do seem might be Earth-grazers skimming far throughout the highest of the environment.

Layer up much more warmly than you think about you may want; keep in mind about radiational cooling! Find a darkish open spot with no native lights to get in your eyes, lie again in a reclining garden chair, and gaze up into the stars. Relax and be affected person.

Want to do extra? This year the International Meteor Organization is asking for assist in figuring out the impact of vivid moonlight on meteor exercise, via cautious counts for at least one hour and cautious determinations of your limiting magnitude. See Bob King’s Precious Hours with the Geminids.


■ The Summer Triangle is sinking decrease within the west because the season turns, and Altair is the primary of its stars to go (as seen from mid-northern latitudes). Start by recognizing vivid Vega, magnitude zero, within the northwest proper after darkish. The brightest star above it’s Deneb. The Triangle’s third star, Altair, is farther to Vega’s left or decrease left. How late into the evening, and into the advancing season, can you retain Altair in view?


■ This night, spot orange Aldebaran about two fists at arm’s size decrease left of the Moon. Now look in the other way from the Moon a little much less far, and simply a bit up from there, and also you’re at the brightest two or three stars of Aries. Of all of the zodiac constellations, Aries has by far the smallest distinctive sample of its foremost stars.


■ Left of Orion after dinnertime is the constellation Gemini. Castor and Pollux, the pinnacle stars of the Gemini stick-figure twins, are at its left finish; the twins are mendacity on their sides. Castor is the upper one.

Moon passing Pleiades and Aldebaran in Taurus, Dec. 16-18, 2021
The Moon crosses Taurus because it waxes towards full, on the evening of the 18th.

At nightfall on the sixteenth, the gibbous Moon remains to be to the precise of the road from Aldebaran to the Pleiades, as drawn right here for the center of North America. Later within the evening, it crosses that line.

■ Comet Leonard has been rising simply above the southwest horizon in night twilight, a little bit greater every day. But you may be wanting by a not-fully-dark sky.

This night presents a simple pointer to the precise spot to look at with binoculars. In the southwest, draw a line from modest Saturn diagonally down by sensible Venus, prolong the road on by half once more as far or simply a little extra, and there you’re!

When to look? Fifty minutes after sundown is likely to be a time to start out looking with binoculars or a wide-field telescope. But the most effective time window (if any) between a too-bright sky and a too-low comet will rely in your latitude and the readability of the air.

The farther south you’re the higher. If you are as far north as 40°N (Denver, New York), Comet Leonard might be 8° above the horizon 50 minutes after sundown. Seen from 30°N (New Orleans, the Gulf Coast) it is going to be 10° up at that point. Good luck.


■ Have you ever watched a Sirius-rise? Find an open view proper right down to the east-southeast horizon. Watch there for Sirius to return up about two fists at arm’s size beneath Orion’s vertical Belt. Sirius rises someday round 8 p.m. now relying in your location.

About quarter-hour earlier than Sirius-rise, a lesser star comes up barely to the precise of there: Beta Canis Majoris or Mirzam, a title meaning “The Announcer.” What Mirzam proclaims is Sirius. You’re not prone to mistake the 2; the second-magnitude Announcer is just a twentieth as vivid because the King of Stars about to make his entry.

When a star may be very low it tends to twinkle slowly, usually in vivid colours. Sirius is vivid sufficient to show these effects well, particularly with binoculars.


■ As twilight fades out this night, use binoculars or a telescope to strive for Comet Leonard 5° beneath Venus within the southwest. It ought to nonetheless be about magnitude 6. Good luck.

■ Full Moon tonight (precisely full at 12:35 a.m. tonight EST; 9:35 p.m. PST). The Moon shines between the horntip stars of Taurus, Beta and Zeta Tauri, as proven above. It’s at apogee, making this a “mini-moon” very barely smaller than common: the alternative of a “supermoon” at perigee.

By midnight the Moon may be very excessive within the south, not removed from the zenith. The full Moon of the Christmas season rides greater throughout the sky at midnight than at another time of year, thus “giving lustre of midday to objects below.”

Why? December is the month of the solstice, when the Sun is farthest south within the sky. So, that is when the total Moon (reverse the Sun) is farthest north. In crossing the sky, it behaves like a pale, chilly June Sun within the evening.


This Week’s Planet Roundup

Mercury is hidden deep within the sundown.

Venus, a dazzling magnitude –4.8, shines within the southwest throughout and after twilight. It’s drawing nearer to Earth and nearer to our line of sight to the Sun. Thus we see its crescent enlarge from a large 45 arcseconds to 50 arcseconds tall this week, whereas it thins from 20% to solely 13% sunlit. Any telescope is sufficient to maintain watch!

Mars, far and faint at magnitude +1.6, is low within the daybreak in Libra. Look for it a little above the southeast horizon about 50 minutes earlier than sunup, way down beneath Arcturus and Spica.

Jupiter with Great Red Spot and two dark barges on Nov. 22, 2021.
Jupiter on November twenty second, imaged by Christopher Go within the Philippines. South is up. Because Jupiter is much previous opposition, its following (japanese) edge is barely shaded. Jupiter has shrunk to 37 arcseconds vast now however remains to be price watching! Get your scope on Jupiter and Saturn in twilight earlier than they transfer decrease. Moreover, the seeing usually steadies in twilight.

The South Equatorial Belt, with the Great Red Spot in its southern edge, is usually pale. The North Equatorial Belt is comparatively darkish red alongside its south edge and sports activities two darkish red barges within the picture above.

Color and brightness contrasts are exaggerated right here, in comparison with Jupiter’s whiter, flatter visible look. This is finished in nearly each photograph of Jupiter you ever see, as a way to carry out particulars.

Jupiter, crossing from Capricornus into Aquarius, shines within the south-southwest at nightfall about three fists at arm’s size higher left of Venus. At magnitude –2.2 it is second in brightness solely to Venus.

Look two fists decrease left of Jupiter for Fomalhaut, magnitude +1.2.

Saturn, in Capricornus, is halfway between Jupiter and Venus. At magnitude +0.7, Saturn is only one/15 Jupiter’s brightness.

Saturn units round 8 p.m. Jupiter follows it down a little greater than an hour later.

Uranus (magnitude 5.7, in Aries north of the pinnacle of Cetus) may be very excessive within the southeast in early night. See Bob King’s story and finder chart.

Neptune (magnitude 7.9, in Aquarius beneath the Great Square of Pegasus and the Circlet of Pisces) is sort of excessive within the south-southwest in early night.

All descriptions that relate to your horizon — together with the phrases up, down, proper, and left — are written for the world’s mid-northern latitudes. Descriptions and graphics that additionally rely upon longitude (primarily Moon positions) are for North America.

Eastern Standard Time, EST, is Universal Time (additionally referred to as UT, UTC, GMT, or Z time) minus 5 hours.

Want to turn out to be a higher astronomer? Learn your way across the constellations. They’re the important thing to finding every part fainter and deeper to hunt with binoculars or a telescope.

This is an out of doors nature passion. For an easy-to-use constellation information masking the entire night sky, use the large month-to-month map within the middle of every situation of Sky & Telescope, the journal of the American Astronomical Society.

Once you get a telescope, to place it to good use you may want a detailed, large-scale sky atlas (set of charts). The primary customary is the Pocket Sky Atlas (in both the original or Jumbo Edition), which exhibits stars to magnitude 7.6.

Pocket Sky Atlas cover, Jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and lots of of telescopic galaxies, star clusters, and nebulae amongst them. Shown right here is the Jumbo Edition, which is in exhausting covers and enlarged for simpler studying outdoor by red flashlight. Sample charts. (*18*).

Next up is the bigger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; practically 3 times as many. The subsequent up, as soon as your way round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And make sure you learn How to Use a Star Chart with a Telescope.

You’ll additionally need a good deep-sky guidebook, similar to the large Night Sky Observer’s Guide set by Kepple and Sanner.

Can a computerized telescope exchange charts? Not for newcomers, I do not assume, and never on mounts and tripods which are lower than top-quality mechanically, which means heavy and costly. And as Terence Dickinson and Alan Dyer say of their (*10*), “A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand.”

Audio sky tour. Out underneath the night sky along with your
earbuds in place, hearken to Kelly Beatty’s month-to-month
podcast tour of the heavens above. It’s free.

“The dangers of not thinking clearly are much greater now than ever before. It’s not that there’s something new in our way of thinking, it’s that credulous and confused thinking can be much more lethal in ways it was never before.”
            — Carl Sagan, 1996

“Facts are stubborn things.”
            — John Adams, 1770

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