Binocular Comet ZTF! Comet C/2022 E3 (ZTF), known to its friends as ZTF E3, has been brightening ever since the automated Zwicky Transient Facility discovered it at 17th magnitude last March. Now it's finally having its weeks in the sun (so to speak), crossing the northern sky. As of January 18th it's about magnitude 6.0, on its way to maybe 5.5 at its brightest around the end of January and the beginning of February.

Comet C/2022 E3 (ZTF) on January 3, 2023, imaged from Sweden by Frosth Astrophotography
Comet C/2022 E3 (ZTF) on January 3, 2023, imaged from Sweden by Marten Frosth. This is a stack of 40 one-minute exposures taken with an 80-mm refractor through L, R, G, and B color filters and assembled by sophisticated methods. The characteristic cometary green color is emission by C2 (dicarbon) molecules fluorescing in the sunlight.

The comet should be in reach of binoculars even through a somewhat light-polluted sky if you have a chart that pinpoints the location to examine each night, and you know the constellations well enough to match the chart to your sky outdoors. The comet may even become dimly visible to the naked eye in a really dark, moonless sky again, if you know the right spot to examine.

See Bob King's Circumpolar Comet ZTF (C/2022 E3) is Here! with the finder chart that you need, as well as a table of the best observing times by date and the moonlight situation. On the chart, the dates on the comet's track are for oh Universal Time, which falls on the evening of the previous date in North America.

As of Wednesday night January 18-19 the comet is in northernmost Boötes, some 20° up in the northeast by 1 a.m. and highest in a dark sky before the first light of dawn. (That means go out at least 2 hours before sunrise to leave some observing time after you set up.) The Moon is now out of the picture.

The comet is traveling north, and by January 26th it's nicely up from 9 p.m. until dawn as it reaches the Little Dipper. It will pass Kochab on the North American night of the 27th and Polaris on the 29th and 30th, but by then moonlight will be a growing interference in the evening, with the Moon not setting until later and later.


■ Orion leans bravely upward in the east-southeast after dark this week, and by 7 p.m. he's nice and high in the southeast with Sirius shining below him. Orion stands upright and highest by 10 p.m.

■ How well do you know Orion's Sword telescopically, beyond the familiar M42 and M43 nebulae and M42's Trapezium? Many double stars and groupings await. Use Ken Hewett-White's "Sword Scene" article, chart, and list in the January Sky & Telescope, page 54.

■ Below Orion's feet, you may know Lepus the Hare. But how about the scattering of Columba the Dove below Lepus? See Fred Schaaf's "Evenings with the Stars" column in the January Sky & Telescope, page 45. By late evening when the Orion-Lepus-Columba stack is highest in the south, the constellation chart to use is the one in the center of the February issue.

Venus and Saturn in the sunset, Jan. 13, 2023
Venus shines just a little higher in twilight this week than last; look low in the west-southwest. Saturn is moving down toward it more rapidly. Saturn is only 1/75 as bright as Venus (magnitude +0.8), so it emerges into view somewhat later. This evening it's nearly a fist at arm's length to Venus's upper left.

That little star 1.4° to Saturn's lower left is Delta Capricorni, magnitude 2.8. For this you'll need to wait until twilight is nearly over.


■ Last-quarter Moon tonight (exactly so at 9:10 p.m. EST). The Moon rises around midnight or 1 a.m., with Spica about half a fist to its upper right. Brighter Arcturus is two fists to the Moon's upper left. Even in cold January, spring stars emerge from hiding if you go out late enough!


■ The Gemini twins lie on their sides these January evenings, well up in the east left of Orion. Their head stars, Castor and Pollux, are farthest from Orion, one over the other. (Castor is the top one, slightly the fainter of the two.) The Castor figure's feet are just left of Orion's very dim Club. The bright star below Gemini's legs is Procyon in Canis Minor.


■ More action at Jupiter: At 8:30 p.m. EST, Jupiter's largest moon Ganymede slowly disappears behind Jupiter's western limb, just as Io is approaching Jupiter's opposite limb. Io crosses the limb onto Jupiter's face 31 minutes later, at 9:01 p.m. EST. Then at 10:16 EST Io's following shadow crosses onto Jupiter's eastern edge. In the Eastern time zone Jupiter is already setting by then, but westerners still have a decent view, seeing permitting.

This cosmic playfulness around Jupiter has been carrying on steadily, day by day and hour by hour, since the solar system formed 4.6 billion years ago. Only in the last ten-millionth of that time has any living creature had a telescope to witness it. Consider yourself lucky.


■ The big Northern Cross in Cygnus, topped by Deneb, is roughly upright in the west-northwest after dinnertime. By 7 p.m. it's standing on the horizon. How upright it stands there depends on your latitude.

■ Early in the dawn of Wednesday the 18th, look southeast for the waning crescent Moon with Antares 2° or 3° to its right, as shown below. Bring binoculars in case the sky is getting too bright.

And see if you can spot Mercury yet, nearly three fists to the Moon's lower left.

The Moon consorts with Antares early on Wednesday morning the 18th. Can you detect Mercury by that date? It's about 27° lower left of the Moon.

These scenes are always drawn for a skywatcher near 40° north latitude. Seen from south of there, Mercury will appear somewhat higher. Seen from north of 40°, Mercury will be lower.


■ If your sky is even moderately dark, try tracing out the winter Milky Way now arching very high. In early evening it extends up from the west-northwest horizon along the Northern Cross of Cygnus, up and over to the right past dim Cepheus and then through Cassiopeia high in the north, then to the right and lower right through Perseus and Auriga, down between the feet of Gemini and Orion's dim club, and on down toward the east-southeast horizon between Procyon and Sirius.


■ As we enter the coldest depths of winter (on average), the bowl of the Little Dipper hangs straight down from Polaris around 7 or 8 p.m. as if (per Leslie Peltier) from a nail on the cold north wall of the sky.

The brightest star of the Little Dipper's dim bowl is Kochab, the bowl's lip. It's the equal of Polaris. Kochab itself passes precisely below Polaris about 30 minutes before the center of the bowl.

The Big Dipper, meanwhile, is creeping up low in the north-northeast. Its handle is low and its bowl is to the upper right.


■ Sirius twinkles brightly after dinnertime below Orion in the southeast. Around 8 or 9 p.m., depending on your location, Sirius shines precisely below fiery Betelgeuse in Orion's shoulder. How accurately can you time this event for your location, perhaps judging against the vertical edge of a building? Of the two, Sirius leads early in the evening. Betelgeuse leads later.

Continue the line from Betelgeuse through Sirius on down, and it runs right along Canis Major's back by another 10° to the dog's rear end: Delta Canis Majoris, or Wezen.

Saturn is fast closing in on Venus. This evening, binoculars may show 3rd-magnitude Delta Capricorni forming a little triangle with them.


■ Zero-magnitude Capella high overhead, and equally bright Rigel in Orion's foot, have almost the same right ascension. This means they cross your sky’s meridian at almost exactly the same time: around 9 or 10 p.m. now, depending on how far east or west you live in your time zone. So, whenever Capella passes its very highest, Rigel always marks true south over your landscape, and vice versa.

Capella goes exactly through your zenith if you're at latitude 46° north: Portland, Oregon; Montreal; Portland, Maine; central France; Odesa.

■ New Moon (exact at 3:53 p.m. EST.)


■ Venus and Saturn reach their conjunction ½° apart, as shown below. Use binoculars in bright twilight. And look too for the thin crescent Moon rather far below them.


This Week's Planet Roundup

Mercury emerges into dawn view late this week, climbing and brightening every day. By January 18th it should be in fairly easy view, low in the southeast at magnitude +0.5. Binoculars always help.

On the morning of the 19th look for Mercury 13° left of the waning crescent Moon. Next week Mercury will be brighter and easier in the dawn.

Venus, very bright at magnitude –3.9, shines low in the west-southwest in twilight. It sets around twilight's end. Look for dimmer Saturn to Venus's upper left, closer to it day by day. They're 10° apart on the evening of the 13th, closing to 2° by the 20th. They'll reach conjunction on the 22nd, about ½° apart.

Mars, in Taurus, shines very high in the east-southeast at dusk and near the zenith as you face south by 8 or 9 p.m. Mars continues to fade slowly, from magnitude –0.8 to – 0.6 this week, as it shrinks from 13 to 12 arcseconds wide. Mars-colored Aldebaran, mag +0.8, is 8° or 9° below it.

Mars on Dec. 22, 2022, with Mare Cimmerium and Mare Tyrrhenum
Mars imaged on December 22nd by Christopher Go in the Philippines. South is up. Syrtis Major is the dark arc near the lower right limb. Just above center, the two large, parallel, mottled diagonal bands are Mare Cimmerium (left) and Mare Tyrrhenum. The pointy lower-right end of Mare Cimmerium is Tritonis Sinus. Two small prongs point down from Cimmerium; the darker one is Gomer Sinus. At bottom is the North Polar Cloud Hood.

Jupiter, magnitude –2.3 in Pisces, shines high in the south-southwest in twilight, then sinks toward the southwest. It sets around 10 or 11 p.m. Telescopically, Jupiter has shrunk to 37 arcseconds wide.

Look for the Great Square of Pegasus to Jupiter's upper right through the evening. Extend the line of the Square's upper left side down to the planet. This week Jupiter is still just a trace west (left) of that line. It will cross the line on January 23rd. To help judge this, hold a straightedge up to the sky or stretch a string tightly between your hands.

Jupiter on January 15th, imaged by Christopher Go. South is up, east is right. Notice that Jupiter's eastern limb is shadier than the western limb, since Jupiter is near eastern quadrature with the Sun.

Writes Go, "This is my first image of the year.  Monsoon had been horrible. Imaging Jupiter has become very challenging.  It is getting lower in the sky and closer to my hot roof.  Seeing was very unstable." The Great Red Spot is rotating onto the disk from the east. The black dot is the shadow of Io. "I used the new WinJupos feature of [Galilean] moon derotation [in addition to the standard derotation of the planet during the long series of stacked video frames], and it works perfectly!"

Saturn, magnitude +0.8 in Capricornus, is upper left of brilliant Venus in twilight getting low in the west-southwest. Saturn is 10° from Venus on the evening of January 13th, closing to 2° by the 20th. They'll reach conjunction on the 22nd, about ½° apart.

In late twilight look about two fists at arm's length to Saturn's left for Fomalhaut, and three fists or so to Saturn's right for Altair.

Uranus, magnitude 5.7 in southern Aries, is high in the south in early evening. It displays a tiny, very slightly blue-greenish gray disk 3.6 arcseconds wide. It a telescope at high power it's obviously non-stellar. See the Uranus finder charts in the November Sky & Telescope, page 49.

Neptune, magnitude 7.9 at the Aquarius-Pisces border about 10° west of Jupiter, gets lower through the evening ahead of Jupiter. So try for it right after dark. Neptune is just 2.3 arcseconds wide, again non-stellar in a telescope but requiring more effort than Uranus. See the Neptune finder charts in last September's Sky & Telescope, page 49.

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions and graphics that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time (EST) is Universal Time minus 5 hours. Universal Time is also called UT, UTC, GMT or Z time.

Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Pocket Sky Atlas cover, Jumbo edition
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown here is the Jumbo Edition, which is in hard covers and enlarged for easier reading outdoors by red flashlight. Sample charts. More about the current editions.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, are the even larger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And be sure to read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet as to charts on paper.

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically, meaning heavy and expensive. And as Terence Dickinson and Alan Dyer say in 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 under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
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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mary beth

January 13, 2023 at 10:44 am

Mr. MacRobert, I love the addition of the second Sunday! I don’t know if it’s just this week because of the spectacular conjunction, but I sure hope it’s a new permanent change because it takes you through the weekend. Thank you!

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January 15, 2023 at 6:33 am

Some comet viewing this morning. Observed 0345-0415 EST. Last Quarter Moon 15-Jan-2023 0210 UT. The lovely Last Quarter Moon visible in Virgo when I used 10x50 binoculars and looked at the comet this morning, C/2022 E3 ZTF. Distinct fuzzy with hint of tail. reports apparent magnitude +6.90. Stellarium 1.2 shows 6.97, and Starry Night Pro Plus 8 shows 6.97. Easy to locate using a trio of stars. 4 Herculis, Chi Herculis, and 2 Herculis. These were 4.59 to 5.71 magnitude. The other trio were Phi Bootis, Nu2 Bootis, and Nu1 Bootis. They were about 4.96 to 5.25 magnitude stars. C/2022 E3 ZTF framed by these stars. About 2-degrees angular separation from 4 Herculis and Phi Bootis star too. Clear skies, temperature -3C, winds 360/12 knots. I took a short look this morning, no telescope views. This is my 4th observation of C/2022 E3 ZTF that began on 24-Dec-2022 with apparent magnitude near 8.59.

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January 15, 2023 at 8:29 am

New Jersey Eclipse Fan. Yes, the wood burning stove was running too while I enjoyed some comet views this morning 🙂

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New Jersey Eclipse Fan

January 15, 2023 at 11:58 am

Sounds like an all-around cosmic-comet-comfy experience!

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mary beth

January 15, 2023 at 12:38 pm

Not to mention constellations and COLD!

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New Jersey Eclipse Fan

January 16, 2023 at 1:08 pm

Completely concur!

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mary beth

January 16, 2023 at 9:38 pm


I always call those Conjunction Junction… Do you remember that “school house rock” episode? Very catchy song , I still love to sing it almost 50 years later!

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January 18, 2023 at 7:47 pm

Wake me up when a comet is mag -5 with a 60 degree long tail.....

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mary beth

January 19, 2023 at 10:11 am

Sounds like the kids on your bus! Did they hijack your phone lol. Seriously I bet you will have pretty good viewing conditions?

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January 19, 2023 at 11:56 am

Ha Ha! Yea, it does sound like them. I have seen this comet using bins... I just miss the bright comets that you don't need a star chart to find!

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January 19, 2023 at 12:00 pm

By the way, speaking of the school bus, I viewed Mercury this morning at my first pickup at 0605. Just to the left of the waning moon.

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mary beth

January 19, 2023 at 10:13 am

Just bought Leslie Peltier’s book mentioned above! It’s on kindle now!

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