■ The crescent Moon hangs in the southwest after sunset, as shown below. It aims its curve lower right almost at Mercury, like a bow ready to shoot an arrow. Mercury is about two fists at arm's length from it (during twilight in North America).

Even farther down in the same direction, can you still pick out Jupiter with binoculars? Jupiter is now very nearly on the opposite side of the Sun from us.

Day by day, the waxing crescent Moon in twilight steps up and away up from low Mercury and super-low Jupiter.

■ Once full night has fallen, if your sky is even moderately dark try to trace out the winter Milky Way arching across the sky. In early evening it extends up from the west-northwest horizon along the vertical Northern Cross of Cygnus, up and over to the right past dim Cepheus and 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 Club, and on down to the east-southeast horizon between Procyon and Sirius.


■ "I blame binoculars for my interest in the anatomy of the Milky Way," writes Matt Wedel in his Binocular Highlight column for the January Sky & Telescope. "It was only after I fell in love with binocular observing that I realized how many large-scale structures of the galaxy require wide fields and low magnifications. Among my favorites are OB associations groups of hot, young O- and B-type stars thought to have been born in the same giant molecular cloud."

Orion features these prominently. Orion's Belt and Sword regions are subsets of the sprawling Orion OB 1 Association. "Another subset, Orion OB 1a, hasn't reached the same level of fame," writes Wedel, "but it's an eminently worthy subject for binocular observation." See his column and chart on page 43 of the January issue.


■ After dinnertime in this coldest time of the year, the dim Little Dipper (Ursa Minor) hangs straight down from Polaris, as if, per Leslie Peltier, from a nail on the cold barn wall of the northern sky.

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

■ Algol shines at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 11:01 p.m. EST; 8:01 p.m. PST. Algol takes several additional hours to fade and to rebrighten.


■ 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. Welcome to pre-telescopic astronomy.

■ In early evening the enormous Andromeda-Pegasus complex runs from near the zenith far down to the west. Near the zenith, spot Andromeda's high foot: 2nd-magnitude Gamma Andromedae (Almach), slightly orange. Andromeda is standing on her head. Her head-star (2nd-magnitude Alpheratz) is the top corner of the Great Square of Pegasus. Down from the Square's bottom corner run the stars outlining Pegasus's neck and head, ending at his nose: 2nd-magnitude Enif, also slightly orange.


■ To the right of the Moon in early evening is the Great Square of Pegasus, balancing on one corner. The horizontal diagonal across the Square points left to the Moon, its own length away.


While twilight is still fading on Wednesday the 20th, Mars is still a bit left of straight up from the Moon. They line up exactly vertically a little after dark (for much of North America).

■ First-quarter Moon (exactly so at 4:02 p.m. EST). Mars shines above the Moon in twilight and early evening as shown above. Upper right of Mars are the brightest stars of Aries.

Mars is in conjunction with Uranus this evening! Use binoculars to spot Uranus, magnitude 5.7, lower left of Mars by 1.5°. It's the brightest little "star" at that spot. Left of Uranus by 0.5° is a fainter, magnitude 6.9 star. Those are really the only two things there.

So how wide are 1.5° and 0.5° in your binocs? To get the measure of your binocular's field width, look at those two brightest stars of Aries to Mars's upper right. They're 3.9° apart. Or use the end stars of the Big Dipper's bowl (the Pointers); they're 5.4° apart. Or use Orion's shoulders; they're 7.5° apart. Once you determine the width of your binocular's view, remember it always.

■ Algol should be at minimum brightness for a couple hours centered on 7:50 p.m. EST.


■ 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 p.m. now, depending on how far east or west you live in your time zone. (Capella goes exactly through your zenith if you're at latitude 46° north: Portland, Oregon; Portland, Maine; Montreal; central France.)

So, whenever Capella passes its very highest, Rigel always marks true south over your landscape, and vice versa.


■ Right after dark, face east and look very high. The bright star there is Capella, the Goat Star. To the right of it, by a couple of finger-widths at arm's length, is a small, narrow triangle of 3rd and 4th magnitude stars known as "the Kids." Though they're not exactly eye-grabbing, they form a never-forgotten asterism with Capella.


■ Aldebaran shines below the waxing gibbous Moon this evening (by 4°), as shown below. Spot the Pleiades farther to the Moon's upper right. Far beneath them all is Orion.

The waxing gibbous Moon walks across Taurus from the 22nd through the 24th, stepping through the gap between Aldebaran and the Pleiades. (The Moon in these scenes is always drawn three times its actual apparent size.)

This Week's Planet Roundup

Mercury (brighter than usual at about magnitude –0.7) is emerging into a nice evening apparition low in the fading twilight. Look for it low in the west-southwest about 45 minutes after sunset.

Venus (magnitude –3.9) is very low in the southeast as dawn grows bright. Look for it about 20 or 30 minutes before sunrise.

Mars (about magnitude +0.2, in Aries) shines at its highest in the south in late twilight. It's still high in the southwest as late as 8 or 9 p.m.

Mars continues to fade and shrink into the distance. It's now 9 arcseconds wide in a telescope, maybe still large enough to show some very large-scale surface markings during steady seeing. It's gibbous, 89% sunlit from Earth's point of view. (To get a map of the side of Mars facing you at the date and time you observe, you can use our Mars Profiler. The map there is square, so remember to mentally wrap it onto the side of a globe; features near the map's edges become very foreshortened.)

Jupiter (magnitude –1.9) is finally vanishing from sight in the glare of sunset. See the scene at the top of this page. The earlier in the week you look the better your chance, and bring binoculars. On Friday the 15th Jupiter is still only 6° lower right of Mercury, but the gap between them widens by 1° per day.

Saturn is lost from sight in the glare of the Sun; it's lower right of Jupiter.

Uranus (magnitude 5.7, in Aries) is highest in the south right after dark, just a couple degrees or so from eastward-flying Mars. They're closest together at conjunction, 1.5° apart, on the 20th; see January 20 above. Mars will be within 2° of Uranus from the 18th through the 22nd.

In binoculars Uranus is a little pinpoint "star." But with an apparent diameter of 3.6 arcseconds, it's a tiny, fuzzy ball at high power in even a smallish telescope with sharp optics — during spells of good seeing.

Neptune (magnitude 7.9, in Aquarius) is getting low in the southwest right after dark. Neptune is 2.3 arcseconds wide. Finder charts for Uranus and Neptune.

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 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 known as 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 at night. 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 sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger (and illustrated) Night Sky Observer's Guide 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



Image of Rod


January 19, 2021 at 8:37 am

mary beth, New Jersey Eclipse Fan. I was out last night from 1900 until 2000 EST. I used my 10-inch Newtonian and enjoyed some views of M35 and NGC 2158 open clusters in the same field of view at about 34/35x. Near sunset we had snow flurries move through and then later mostly clear, but suddenly changed to mostly cloudy skies again when altocumulus rolled in, covering the sky. Perhaps tomorrow night, the weather looks better for me and I can view Mars and Uranus about 1.5 degrees angular separation. First Quarter Moon tomorrow evening so the moon will wax eloquently for awhile now too 🙂

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Image of Rod


January 19, 2021 at 9:50 pm

Today before noon I was able to enjoy some views of sunspot AR2797 reported at using my glass, white light solar filter at 40x. Tonight I did enjoy Mars, Uranus, and the waxing crescent Moon. Observed 1730-1830 EST/2230-2330 UT. Sunset near 1714 EST. Some enjoyable views of Mars and Uranus tonight using 90-mm refractor. I also enjoyed views using 10x50 binoculars, easy to see Mars and Uranus in FOV. At 129x, I could see Uranus small blue-green disk (3.6” angular size, 99.9% illuminated) and Mars, larger gibbous shape planet (8.7” angular size, 88.5% illuminated) and much brighter. At 71x, Uranus and two stars formed a triangle shape. The stars were HIP10784 and HIP10730. Lovely early evening view tonight along the ecliptic. I looked at the Moon first at 25x. Good crater detail along the terminator line and some earthshine visible too. At 25x with nearly a 100 arcminute true FOV, Uranus was just outside the FOV with Mars in the eyepiece. Slow motion control adjustments very small to bring Uranus into view. 10x50 binoculars showed the two planets easily in the binocular FOV after 1800 EST.

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