This Week’s Sky at a Glance, December 17 – 25


■ Comet Leonard (C/2021 A1) could be very low within the west-southwest towards the top of night twilight; use binoculars or a wide-field telescope. You’ll must catch the slender time window, if any, between the sky being too brilliant and the comet getting too low; 60 to 75 minutes after sundown is likely to be finest relying in your latitude.Finding the suitable location, at least, will likely be simple! Venus and Saturn information you to the right spot of sky to look at; use the finder chart at the underside of See Comet Leonard at its Best. The dates of the comet symbols there are Universal Time dates; subtract sooner or later to get the North American civil date within the night.

This night the comet’s location is very simple to search out. Just look 5° beneath Venus! (for the mid-latitudes of North America.) That’s a bit lower than the width of a typical binocular’s area of view.

■ Orion strides up away from the east-northeast horizon quickly after darkish now. By 9 p.m. he is excessive within the southeast in full wintry glory.

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

About 15 minutes beforehand, a lesser star comes up barely to the suitable of there: Beta Canis Majoris or Mirzam. Its title means “the Announcer,” and what Mirzam proclaims is Sirius. You’re not prone to mistake the 2; the second-magnitude Announcer is barely a twentieth as brilliant because the King of Stars about to make its entry.

When a star could be very low it tends to twinkle slowly, typically in vivid colours. Sirius is brilliant sufficient to point out these results effectively, particularly with binoculars.

The Moon crosses Taurus because it waxes to full on the 18th.


■ 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 other of a “supermoon” at perigee.

By midnight the Moon could be very excessive within the south, not removed from the zenith. The full Moon of the Christmas season rides larger throughout the sky at midnight than at another time of 12 months, 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 complete Moon (reverse the Sun) is farthest north. In making its means throughout the night time sky, it behaves as a pale, chilly imitation of the June Sun six months in the past.


■ Venus and Jupiter this week proceed to shine brightly throughout twilight within the southwest and south-southwest, respectively. But each are getting decrease now, Venus particularly. As twilight fades, look ahead to dimmer Saturn rising between them.

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

Have you ever tried to discern the crescent of Venus together with your bare eyes? Just a few sharp-eyed individuals can! One was apparently Edgar Allan Poe; see This Week’s Planet Roundup at the underside of this web page.


■ Around the top of twilight, face north and look excessive. Cassiopeia is now a flattened M form canted at about a 45° angle (relying on the place you reside). Just two hours later, the M is horizontal! Constellations passing close to the zenith seem to rotate quickly with respect to your route “up.”

■ You are remembered, Carl Sagan (November 9, 1934 – December 20, 1996).


■ The solstice marks the official begin of winter at 10:59 a.m. EST (15:59 UT). Last night time and tonight are the longest nights of the 12 months within the Northern Hemisphere. The Sun is at its southernmost declination for the 12 months and begins its six-month return northward.

■ 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 brilliant Vega, magnitude zero, the brightest star within the northwest proper after darkish. The brightest one above it’s Deneb. The Triangle’s third star, Altair, is farther to Vega’s left or decrease left. How late into the night time, and into the advancing season, can you retain Altair in view?


■ This is the time of 12 months when M31, the Andromeda Galaxy, passes your zenith quickly after darkish (in case you reside within the mid-northern latitudes). The precise time is dependent upon your longitude. Binoculars will present M31 simply off the knee of the Andromeda constellation’s stick determine; see the large night constellation chart within the heart of Sky & Telescope. Lie in your again with binocs and look straight up. M31 passes precisely via your zenith in case you’re at 41° north latitude.


■ 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 fainter and better one.


■ The Jupiter-Saturn-Venus line at nightfall slowly continues to evolve. Saturn is now a little nearer to Venus; a month in the past it was nearer to Jupiter. And the entire line is sliding farther to the decrease proper.And the road is now rising longer once more, not shorter. If you have been hoping Jupiter was on its method to a conjunction with Venus, nope. Venus is now diving away again down towards the Sun (it passes the Sun in daytime on January eighth). As for Jupiter and Saturn, their very own subsequent conjunction would not come till November 2, 2040.

Jupiter has moved some 6° to the higher left Third-magnitude Delta Capricorni, whereas Saturn has migrated practically to the middle of Capricornus’s dim boat-shape. And are you able to catch Mercury beneath Venus but? Look early!


■ High above Orion shines orange Aldebaran with the massive, free Hyades cluster in its background. Binoculars are the perfect instrument for this cluster given its dimension: its brightest stars (4th and fifth magnitude) span an space about 4° extensive. Higher above, the Pleiades are hardly greater than 1° throughout counting simply the brightest stars.

The essential Hyades stars famously kind a V. It’s presently mendacity on its aspect, open to the left. Aldebaran kinds the decrease of the V’s two ideas.

With binoculars, comply with the decrease department of the V to the suitable from Aldebaran. The very first thing you come to is the House asterism: a sample of stars like a kid’s drawing of a home with a peaked roof. The home is presently upright and bent to the suitable prefer it received pushed.

The House consists of three binocular double stars that kind an equilateral triangle, with every pair dealing with the middle. The brightest pair is Theta1 and Theta2 Tauri. You might discover you could resolve the Theta pair together with your unaided eyes.



This Week’s Planet Roundup

Mercury stays hidden within the sundown for a lot of the week. But by Christmas Eve, search for it in early twilight some 9° beneath Venus as proven above. Next week Mercury will get simpler day by day.

Venus, sensible at magnitude –4.7, shines low within the southwest in twilight. It’s a dramatic crescent now in a telescope and even good binoculars, because it attracts nearer to Earth and nearer to our line of sight to the Sun. This week we see its crescent enlarge from 50 to 55 arcseconds tall, whereas thinning from 13% to solely 8% sunlit.

A Naked-Eye Venus Challenge! Some individuals can resolve the crescent of Venus with their unaided eyes when it is this huge. Mere 20/20 imaginative and prescient most likely is not ok; success might await the eagle-eyed with 20/15, 20/12, 0r (uncommon) 20/10 imaginative and prescient. Try early in twilight earlier than the sky turns into too darkish and Venus too glary. Look lengthy and thoroughly and please report your outcomes to Sky & Telescope’s Bob King,, as advised within the May 2020 difficulty, web page 49.You might enhance your probabilities by sighting via a clear, spherical gap in a stiff piece of paper about 1 mm, 2mm, or 3mm in diameter subsequent to your eye (attempt all of them). It will masks out optical aberrations which can be frequent away from the middle of your eye’s cornea and lens. Try every eye.One one who apparently succeeded was Edgar Allan Poe. An novice astronomer since boyhood, he used a naked-eye sighting of Venus’s crescent because the central occasion in his poem “Ulalume” (1847) close to the top of his life. Before daybreak, a bereaved lover roams a misty October woodland accompanied by “Psyche, my soul.” Ahead of them low within the east, the place the constellation Leo ascends earlier than daybreak in mid-autumn, they witness the new-risen Venus, star of romantic love in Roman mythology, coming “up through the lair of the Lion.” Poe refers back to the planet as Astarte — the wilder, extra wanton Greek model of the Romans’ Venus goddess:

And now, because the night time was senescent,And star-dials pointed to morn —As the star-dials hinted of morn —At the top of our path a liquescentAnd nebulous lustre was born,Out of which a miraculous crescentArose with a duplicate horn—Astarte’s bediamonded crescentDistinct with its duplicate horn.

Poe compares its passionate brilliance to cooler, extra composed Dian, the horned crescent Moon, and urges Psyche ahead:Let us on by this tremulous gentle!Let us bathe on this crystalline gentle!

But Psyche, who is aware of higher, is terrified, and this being Poe, the journey would not finish effectively.

Poe’s narrator peering at a pre-dawn crescent Venus, “distinct with its duplicate horn,” as Psyche, his winged soul, begs him away. Studies by Dante Gabriel Rossetti, circa 1847–1848. The figures on the suitable are a preliminary sketch, adopted by the extra highly effective model on the left.

Poe wrote “Ulalume” within the fall of 1847. Before daybreak on November 4, 1847, a crescent Venus and crescent Moon (“Dian”) certainly hung close to one another low within the east beneath Leo — in Poe’s “lair of the Lion,” the sky space from which the standard Leo determine stalks upward.Venus was there a couple weeks earlier as effectively, in the course of the mid- and late “lonesome October” of that almost all immemorial 12 months, as a bigger, thinner, extra simply resolvable crescent, although Dian at that point was absent.

Mars, far and faint at magnitude +1.6, could be very low within the daybreak this week far beneath excessive Arcturus. Mars is crossing higher Scorpius. Use binoculars to see that Mars is almost between Delta and Beta Scorpii on the mornings of December 17th and 18th, and on the 19th that it is virtually on high of the fainter Omega1 – Omega2 Scorpii pair.

Marslike Antares, in the meantime, is beneath or decrease proper of the planet; their separation closes from 8° to five° this week.Mars is on the far aspect of its orbit from us, so in a telescope it is simply a tiny fuzzblob Four arcseconds extensive.

Jupiter, magnitude –2.2 at the Aquarius-Capricornus border, shines within the south-southwest at nightfall about three fists at arm’s size higher left of Venus. Look two fists decrease left of Jupiter for Fomalhaut, magnitude +1.2.

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

Saturn units by 7 or Eight p.m. Jupiter follows it down about 1½ hours later.

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

Neptune (magnitude 7.9, in Aquarius) is much less excessive within the south-southwest after darkish.

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 known as UT, UTC, GMT, or Z time) minus 5 hours.

Want to turn into a higher astronomer? Learn your means 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 outside nature passion. For an easy-to-use constellation information protecting the entire night sky, use the large month-to-month map within the heart of every difficulty of Sky & Telescope, the journal of the American Astronomical Society.

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

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and a whole bunch of telescopic galaxies, star clusters, and nebulae amongst them. Shown right here is the Jumbo Edition, which is in laborious covers and enlarged for simpler studying outside by pink flashlight. Sample charts. More concerning the present editions.

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 you realize your means 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, reminiscent of the large Night Sky Observer’s Guide set (2+ volumes) by Kepple and Sanner.

Can a computerized telescope substitute charts? Not for inexperienced persons, I do not assume, and never on mounts and tripods which can be lower than top-quality mechanically, which means heavy and costly. And as Terence Dickinson and Alan Dyer say of their Backyard Astronomer’s Guide, “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 beneath the night sky with yourearbuds in place, take heed to Kelly Beatty’s monthlypodcast 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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