■ The "Summer" Triangle is sinking lower in the west, and Altair is the first of its stars to go (for mid-northern skywatchers). Start by spotting bright Vega, magnitude zero, in the northwest right after dark. The brightest star above Vega is Deneb. Altair, the Triangle's third star, is farther to Vega's left or lower left. How late into the night, and into the advancing season, can you keep Altair in view?

If you live as far south as Miami, Altair and Vega set at the same time. Seen from farther north than that, Altair is the first to go.


■ Have you ever watched a Sirius-rise? Find an open view right down to the east-southeast horizon, and watch for Sirius to rise about two fists at arm's length below Orion's vertical belt. Sirius rises sometime around 8 p.m. now, depending on your location.

About 15 minutes before Sirius-rise, a lesser star comes up barely to the right of there: Beta Canis Majoris or Mirzam. Its name means “The Announcer,” and what Mirzam announces is Sirius. You’re not likely to mistake them; the second-magnitude Announcer is only a twentieth as bright as the king of stars about to make his royal entry.

When a star is very low it tends to twinkle slowly, and often in vivid colors. Sirius is bright enough to show these effects well, especially with binoculars.

Moon with Saturn, Dec. 17, 2023
The Moon's first meetup with an easy naked-eye planet this lunation comes on Sunday evening the 17th, when the Moon is 3° below or lower left of Saturn in early evening (for North America).


■ This evening, spot Saturn about 3° upper right of the Moon as shown above. The Moon is 1.3 light-seconds from us. Saturn is currently 84 light minutes away in the background, almost 4,000 times farther from us.

■ Algol dips to its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 6:17 p.m. EST. Algol takes several additional hours to rebrighten. Comparison-star chart.


■ This is the time of year when Orion shines in the east-southeast after dinnertime, walking upward. He's well up now, but his three-star Belt is still nearly vertical.

The Belt points up toward Aldebaran and, even higher, the Pleiades. In the other direction, it points down to where bright Sirius will rise around 8 p.m. to twinkle furiously.


■ First-quarter Moon (exact at 1:39 p.m. EST). Upper right of it after dinnertime is the Great Square of Pegasus, starting to tilt up on one corner. The Square's upper left edge points diagonally down nearly at the Moon.


■ The Moon is approaching Jupiter night by night, as shown below.

To the right of the Moon this evening (outside the frame) is the Great Square of Pegasus. The line between two opposite corners of the Great Square now points roughly at the Moon.

Cows may not jump over the Moon, but the Moon jumps over Jupiter between this Thursday and Friday evenings.

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


■ Now Jupiter is only about 7° left of the Moon in early evening. Watch then draw closer together through the night.

■ Tonight is the longest night of the year (in the Northern Hemisphere); the solstice is at 10:27 p.m. EST. That's when the Sun stands still in declination, then begins its six-month northward return toward the summer solstice next June 20th.


■ The Moon has passed Jupiter in the last 24 hours. The bright planet now shines to the Moon's right at dusk; upper right of it later.


■ The waxing gibbous Moon is about 4° or 5° to the right of the Pleiades in early evening (for North America). Binoculars help with the Pleiades through the moonlight.

Watch the Moon draw closer to them hour by hour, finally passing only about 1° or 2° south of them shortly before setting in the northwest around the first light of dawn Sunday morning.


■ And now the bright gibbous Moon, two days from full, has jumped to the lower left (east) of the Pleiades in early evening. It forms a flattened, nearly isosceles triangle with the Pleiades above it and Aldebaran below.

Around 11 p.m. tonight the Moon shines just about as close to the zenith as you will ever see it (from your mid-northern latitude), "casting lustre of midday on objects below." Your Moon shadow at that time will be the shortest you'll ever see it. Go look.

The Moon will do very nearly the same close zenith pass about an hour later each night for the next several nights. The Moon will be full on the night of the 26th.

Sirius and Procyon in the balance. Sirius, the Dog Star, sparkles low in the east-southeast as evening advances. Procyon, the Little Dog Star, shines in the east about two fist-widths at arm's length to Sirius's left.

But directly left? That depends. If you live around latitude 30° (Tijuana, New Orleans, Jacksonville), the two canine stars will be at the same height above your horizon soon after they rise. If you're north of that latitude, Procyon will be higher. If you're south of there, Sirius will be the higher one. Your eastern horizon tilts differently with respect to the stars depending on your latitude. Because the Earth is round.

This Week's Planet Roundup

Mercury is "combust," to use an old astronomical term: out of sight in the glare of the Sun.

Venus, magnitude –4.1 in Libra, shines as the bright "Morning Star" in the southeast before and during dawn. It's not as high as it was a month or two ago.

Venus rises above the east-southeast horizon about 1½ hours before dawn's first light. Watch for it to come up three or four fists at arm's length to the lower right of Arcturus, the brightest star twinkling high in the east.

Mars is out of sight behind the glare of the Sun.

Jupiter, magnitude –2.7 in Aries, is the bright white dot dominating the high southeast to south these evenings. It stands at its highest in the south around 8 p.m. It has shrunk a little since opposition, but it's still a good 46 arcseconds wide in a telescope.

Jupiter and Io on Dec. 2, 2023
Jupiter on December 2nd, imaged by Christopher Go. South here is up. Bright Europa is about to exit the planet's upper left (south preceding) limb. Its shadow follows along behind. Between them here and a bit above is the row of three white ovals in the South Temperate Zone. The gradually shrinking "Great" Red Spot is in view. To its preceding side, the south part of the South Equatorial Belt remains especially dark. We've adjusted color and contrast here to approximate Jupiter's visual appearance.

Saturn, magnitude +0.9 in Aquarius, glows yellowish lower in the south-southwest just after dark. Fomalhaut, similarly bright, twinkles roughly two fists at arm's length to Saturn's lower left. Saturn declines toward the southwest as evening progresses and sets around 9 or 10 p.m. So get your telescope on it early!

Saturn on Nov 1, 2023, with Rhea and Dione
Saturn on November 1st, imaged by Christopher Go. South is up. Two of Saturn's moons were nearly in conjunction with it: Dione directly above it here, and larger Rhea upper left.

Uranus, magnitude 5.6 in Aries, awaits your binoculars in the darkness 14° east of Jupiter. In a telescope at high power Uranus is a tiny but distinctly nonstellar ball, 3.8 arcseconds in diameter. Locate and identify it using the finder charts in the November Sky & Telescope, pages 48-49.

Neptune, fainter at magnitude 7.9, is at the Aquarius-Pisces border 23° east of Saturn and is still high in the early-evening dark. Neptune is only 2.3 arcseconds wide: harder to resolve as a ball than Uranus, but definitely nonstellar at high power.

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. UT is also known as 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 a more detailed 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 much more 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 all 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 mag 9.75). And 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 computerized telescopes replace charts? Not for beginners I don't think, especially not on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning the sky. 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."

But finding a faint telescopic object the old-fashioned way with charts isn't simple either. Learn the tricks at How to Use a Star Chart with a Telescope

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the naked-eye 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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December 15, 2023 at 7:34 pm

When the Moon culminates on Dec 25th and 26th, it will only be 2 degrees South of directly overhead as from Houston, and it will pass 2 degrees ~North (!)~ of overhead as seen from Miami.

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Alexander Vasenin

December 16, 2023 at 2:01 am

No word about the solstice on Thursday?

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December 16, 2023 at 9:16 pm

Alexander Vasenin, good observation 🙂 I went back and checked the Skygazer's Almanac 2023 sent out in the January 2023 issue of Sky & Telescope. Yes indeed, December 21 2023 is when winter begins. The solstice 10:27 PM EST, shortest day day, 9 hours 20 minutes at latitude 40 degrees north. Depending upon weather conditions, I may use my 90-mm refractor telescope to view the Sun with my solar filter on the winter solstice.

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December 20, 2023 at 4:21 pm

"Saturday December 23
Watch the Moon draw closer to (the Pleiades) hour by hour, finally passing only about 1° or 2° south of them shortly before setting in the northwest around the first light of dawn Sunday morning."

The Moon will occult the Pleiades as seen from parts of the Southern Hemisphere.
The series began in August with an occultation visible near the South Pole. Occultations will be viewable in the Northern Hemisphere in 2024.

Beta Tauri also started its series in August, again starting in the extreme Southern Hemisphere. However its series won't move far enough north to reach most of the Northern Hemisphere.

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December 21, 2023 at 11:12 am

I did enjoy some solstice viewing this morning.

Observed 0915-1015 EST/1415-1515 UT. Nine active region sunspots reported on the Sun today for the winter solstice at site. reports – “HAPPY SOLSTICE! Today is the shortest day of the year in the northern hemisphere, and the longest day in the south--that is, it's the "December solstice." The exact moment of the solstice is Thursday, Dec. 21st, at 10:27 p.m. EST, when the sun stops moving south and starts moving north again. This event marks the beginning of winter in the north and summer in the south.” Observing using my 90-mm refractor telescope with glass white light solar filter, I could see the sunspot active regions with plage areas around several. I enjoyed views from 25x to 40x using TeleVue 40-mm plossl, TeleVue 32-mm plossl, and Orion Sirius 25-mm plossl for 40x views. Good details and some active regions like AR3529, numerous smaller dark cores visible along with the lighter areas surrounding the dark core. At 40x, about 7.5 arcsecond resolution so on the Sun about 5353 km diameter visible (Sun about 0.984 au). Earth size today about 18 arcseconds. reported "Growing sunspot AR3529 has a beta-gamma magnetic field that poses a threat for strong M-class solar flares. Credit: SDO/HMI" This active region obvious along with AR3521, AR3526, AR3528, all larger than earth size active regions this morning. AR3519, AR3530, and AR3531 showed many plage areas too. I used a red and yellow filter with my eyepieces at times. The weather was very good with clear skies, temperature -1C, winds 360/4 knots and some altocumulus clouds approaching from the north with frost over the fields I viewed from. Pleasant winter solstice telescope time today 🙂

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mary beth

December 21, 2023 at 12:20 pm

Beautifully descriptive report Rod! Hope you chopped lots of wood this year! Happy Winter to you and yours!

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December 21, 2023 at 12:39 pm

I did chop plenty, some 3 cords or more 🙂 Used the wood burning stove the other night too 🙂 Merry Christmas mary beth 🙂

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mary beth

December 21, 2023 at 6:25 pm

Merry Christmas Rod!

p.s. If your grandson comes to visit in the next few days, make sure you watch the Bells of Fraggle Rock…Winter solstice themed, so fun! It’s on YouTube.

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