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The Sky This Week: The Moon’s strange face

Lunar libration shows our satellite from a new angle, while comets, asteroids, and star clusters also take center stage from January 6 to 13.
The Full Moon on January 6, 2023
This simulated image shows how libration makes Luna’s face look almost foreign this month.
NASA’s Scientific Visualization Studio

Friday, January 6
The January Full Moon, often called the Wolf Moon, occurs at 6:08 P.M. EST. Our satellite will dominate the sky tonight, making it a natural target for skygazers who may find it difficult to locate fainter targets with bright moonlight pushing back the darkness.

But really look at Luna tonight; something may seem amiss, particularly if you’re familiar with the face of the Full Moon. It looks almost foreign, thanks to libration, the “nodding” motion we observe due to the Moon’s slightly tilted, slightly eccentric orbit. This month, the effect is even more noticeable because the Full Moon just happens to line up with a time when we get to see parts of the surface normally hidden to us. Tonight, extra portions of the south and east are visible, while the north and west seem oddly truncated. With the Moon up all night, you can step outside at any time to view the strange sight. Over the coming weeks, our satellite will start to “roll” back as the western features currently out of view begin to reappear.

Sunrise: 7:22 A.M.
Sunset: 4:50 P.M.
Moonrise: 4:26 P.M.
Moonset: 7:30 A.M.
Moon Phase: Full
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.
Path of Vesta and Juno in January 2023
Sharing a swim
Vesta and Juno skim just south and east of Neptune (whose position is shown on the 15th) this month. Jupiter sits slightly northeast of this field.
Astronomy: Roen Kelly

Saturday, January 7
Mercury reaches inferior conjunction at 8 A.M. EST. Although it is currently lost to sight, don’t worry — it will soon reappear in the morning sky for early risers to enjoy. Ambitious observers can try to catch it by the end of this week.

Asteroid 4 Vesta is making its way through Aquarius this month. About two hours after dark, when it is still some 30° high, look for the 8th-magntude world just south of the broad triplet of ψ1, ψ2, and ψ3 Aquarii, located about 3° south of Phi (ϕ) Aquarii. You should pick Vesta up easily in binoculars or any small telescope. As an added bonus, Neptune lies 8° north-northeast of Vesta, while mighty Jupiter — visible to the naked eye but beautiful through binoculars or a scope — is 16° northeast.

You can even net a second asteroid nearby: Some 10.7° northeast of Vesta is 3 Juno. Note, though, the fainter, 9th-magnitude world is a bit harder to spot. You’ll find it some 4.5° west-northwest of 4th-magnitude Iota (ι) Ceti.

Sunrise: 7:22 A.M.
Sunset: 4:51 P.M.
Moonrise: 5:25 P.M.
Moonset: 8:15 A.M.
Moon Phase: Waning gibbous (99%)

Sunday, January 8
The Moon reaches apogee, the farthest point from Earth in its orbit, at 4:19 A.M. EST. At that time, it will sit 252,562 miles (406,459 kilometers) away.

Asteroid 2 Pallas reaches opposition at 2 P.M. EST. It’s currently located near the back leg of Canis Major, who follows Orion up into the southeastern sky after dark. Pallas is just 1.3° north of magnitude 3.5 Kappa (κ) Canis Majoris, glowing at magnitude 7.7 — easy to spot with binoculars or a telescope. Note, though, that the bright Moon is relatively nearby, which may make finding the main-belt world a bit tricker than usual.

If you’d like an easier target, skip over to 5th-magnitude 145 Canis Majoris, sometimes called the Winter Albireo. It lies about 11° northeast of Kappa and just 3.5° northeast of Wezen (Delta [δ] Canis Majoris). Zoom in with your telescope and you’ll split this star into an orange and blue double. The two are separated by roughly 26" and reminiscent of — you guessed it — Albireo in Cygnus the Swan. That star is most visible during summer nights, while Canis Major rules the wintertime night sky, earning this double its name.

Sunrise: 7:22 A.M.
Sunset: 4:52 P.M.
Moonrise: 6:25 P.M.
Moonset: 8:53 A.M.
Moon Phase: Waning gibbous (97%)

Monday, January 9
With a bright Moon in the sky most of the night, any deep-sky observing we might want to do is limited to the short window between sunset and moonrise.

As darkness falls, Perseus the Hero is high in east. This constellation is home to the famous double cluster, two open clusters cataloged as h and Chi (χ) Persei. Visible to the naked eye from a dark location as two fuzzy, 4th-magnitude “stars,” these clumps of young stars can be captured through binoculars or a small scope. In fact, lower power is better, as it will show both at once, sitting some 0.5° apart and situated about 4.5° northwest of 4th-magnitude Miram (Eta [η] Persei).

Also listed as NGC 869 and NGC 884, the former sits just east of the latter. Both contain rich fields of stars, with differently colored suns readily apparent throughout. This pair is easy to find and enjoy, making it a favorite of beginning and seasoned observers alike.

Sunrise: 7:22 A.M.
Sunset: 4:53 P.M.
Moonrise: 7:28 P.M.
Moonset: 9:24 A.M.
Moon Phase: Waning gibbous (93%)
Messier 79
Though the photographer admits it was challenging to get this image, the result shows the stunning beauty of globular cluster M79 in Lepus.
Kevin Gill (Flickr)

Tuesday, January 10
Lepus the Hare is often depicted crouching at the feet of Orion the Hunter, possibly so the Hunter’s dogs — Canis Major and Minor — won’t find him. But tonight, we’re on the lookout for this celestial rabbit, as we track down the globular cluster M79.

About two hours after sunset, Orion is already prominent in the east. Lepus lies directly south of the Hunter’s figure, with its magnitude 2.6 alpha star roughly in the center of the constellation. Third-magnitude Beta (β) Leporis lies 3° south-southwest of Alpha (α). Once you’ve found these two stars, use them as pointers — follow the line between them in the same direction for just over the distance they stand apart, and you’ll run smack dab into M79, a little less than 4° south-southwest of Beta.

M79 itself spans roughly 9' in diameter and has a total integrated magnitude of 7.8, making it easy to locate with binoculars or a telescope, especially before the bright Moon rises a few hours after sunset. Note, though, that this cluster is tightly packed and difficult to resolve in smaller instruments — you’ll want a larger telescope to transform its fuzzy glow into myriad stars.

Sunrise: 7:22 A.M.
Sunset: 4:54 P.M.
Moonrise: 8:28 P.M.
Moonset: 9:51 A.M.
Moon Phase: Waning gibbous (88%)

Wednesday, January 11
Distant Neptune is floating through the constellation Aquarius, currently in the far northeastern corner of the constellation near its border with Pisces. The magnitude 7.8 planet requires binoculars or a telescope to spot, some 9.5° west of much brighter (magnitude –2.3) Jupiter, which sits near the Circlet of Pisces.

For a while now, Neptune has been passing near a parallelogram of 7th-magnitude field stars. Tonight, the ice giant will slide about 6' due south of HIP 116402, the star marking the northeastern corner of the shape. Neptune will continue to head steadily northeast, finally passing into Pisces in early March. For now, though, it will remain in Aquarius and is best seen early in the evening shortly after dark, when it is still relatively high and your views are unhindered by the turbulent atmosphere near the horizon.

Sunrise: 7:22 A.M.
Sunset: 4:55 P.M.
Moonrise: 9:30 P.M.
Moonset: 10:14 A.M.
Moon Phase: Waning gibbous (81%)
Comet C/2022 E3 (ZTF) early on the morning of January 12, 2023
Comet C/2022 E3 (ZTF)
The morning of January 12, Comet C/2022 E3 (ZTF) sits in Corona Borealis, north-northeast of θ CrB.
Alison Klesman (via TheSkyX)

Thursday, January 12
Mars has spent quite some time in the constellation Taurus, adding a second brilliant ruby point to the Bull’s face alongside the red giant Aldebaran. Today, the Red Planet is stationary at 3 P.M. EST and appears about 8.5° north-northeast of Aldebaran after sunset. Mars will now begin tracking east toward Elnath, the tip of the Bull’s northwestern horn.

A month past opposition, Mars is now magnitude –0.9, still readily apparent to the naked eye. Through a telescope, it spans 13".

Today also marks the day Comet C/2022 E3 (ZTF) reaches perihelion, coming within some 1.1 astronomical units of the Sun (1 astronomical unit, or AU, is the average Earth-Sun distance). ZTF may very well be the best comet of the year and is well within binocular range, already recorded at magnitude 7 earlier this month.

The comet currently rises late, flying through the morning skies and setting early in the evening; your best bet for now is to catch it in the hours before sunrise, when it is high above the horizon in Corona Borealis. Unfortunately, the waning Moon is also prominent in the sky, though it will disappear by next week, leaving your comet viewing unhindered.

A telescope should still allow you to enjoy the comet’s fuzzy coma, located this morning just under 8° northeast of 4th-magnitude Theta (θ) Coronae Borealis. ZTF will cover a large swath of sky in the coming days, so stay tuned for more tips on how to find it as it heads north toward Polaris.

Sunrise: 7:21 A.M.
Sunset: 4:56 P.M.
Moonrise: 10:30 P.M.
Moonset: 10:36 A.M.
Moon Phase: Waning gibbous (73%)

Friday, January 13
Can you spot Mercury yet? The solar system’s speediest planet has now skipped into the morning sky. Some 40 minutes before sunrise, it is 3° high. But although this is far enough above the horizon for anyone with a clear view east to observe, the tiny planet is still dim, just shy of magnitude 2. That means it will likely be invisible without binoculars or, even better, a telescope to pull out its feeble glow from the brightening background. If you can’t quite find it, don’t worry — Mercury will continue to brighten in the coming days, reaching magnitude 0 in less than a week.

But there’s more to challenge yourself with than just Mercury this morning. A few of the sky’s brighter stars might just stand out as pinpricks in the growing dawn, especially an hour or so before sunrise. Look for luminaries such as Altair in Aquila, Vega in Lyra, and Deneb in Cygnus — you might recognize these as the points of the Summer Triangle, which flies high overhead on summer nights. At this time of year, they are rising in the east shortly before the Sun; all three sit to the upper left (north) of Mercury’s position.

Sunrise: 7:21 A.M.
Sunset: 4:57 P.M.
Moonrise: 11:32 P.M.
Moonset: 10:57 A.M.
Moon Phase: Waning gibbous (64%)
Sky This Week is brought to you in part by Celestron.


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