This Week’s Sky at a Glance, January 17 – 26 – Sky & Telescope

FRIDAY, JANUARY 17

■ Here it is the coldest very bottom of the year (on average). But the Summer Star, Vega, is still barely hanging in! Look for it twinkling over the northwest horizon during and shortly after nightfall. The farther north you are the higher it will be. If you’re as far south as Florida it’s already gone.

■ Venus and Saturn, in the southwest during and after dusk, now appear just 2¼° apart as shown above. That’s about the width of your thumb at arm’s length. Saturn is left of Venus. How early can you first see it?

■ With a small telescope, you can watch Jupiter’s moon Io slowly reappear out of eclipse from Jupiter’s shadow at 10:02 p.m. EST; 7:02 p.m. PST. Watch for it a little less than a Jupiter-width off Jupiter’s eastern limb.

An hour and five minutes before that, Jupiter’s Great Red Spot crosses the planet’s central meridian… if the seeing is good enough for you to detect it in your scope.

For all such events, visible worldwide, see the “Action at Jupiter” timetables in the January Sky & Telescope, page 50.

SATURDAY, JANUARY 18

■ Now Venus and Saturn are 2.2° apart, just a trace closer together than they appeared yesterday. And Saturn is now lower left of Venus. Today is their actual conjunction date (meaning conjunction in ecliptic longitude). From now on, Saturn will move farther below Venus each evening.

■ On the other side of the sky in the southeast, Sirius twinkles brightly two fists under Orion’s belt after nightfall is complete. 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 site, perhaps by judging against the vertical edge of a building? Of the two, Sirius leads early in the evening; Betelgeuse leads later.

SUNDAY, JANUARY 19

■ Right after dark, face east and look very high. The bright star there is Capella, the Sun-colored Goat Star (it’s spectral type G2). 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 their goat-mother.

MONDAY, JANUARY 20

■ Zero-magnitude Capella high overhead, and zero-magnitude 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: near Portland, Montreal, Minneapolis, central France, Odesa, Kherson.) So whenever Capella passes its very highest, Rigel always marks true south over your landscape, and vice versa.

This winter, brighter Jupiter is a little to the right of the midpoint between them.

■ The waning Moon, almost last quarter, rises around midnight tonight with Spica just above it (for North America). The Moon draws farther away from Spica as the night’s remaining hours pass, due to the Moon’s eastward motion along its orbit. And by dawn, Spica twists around to the Moon’s upper right due to your observing platform, the Earth, turning in the opposite direction.

TUESDAY, JANUARY 21

■ The Moon is exactly last quarter at 3:31 p.m. EST today; 12:31 p.m. PST. But it doesn’t rise until around 1 a.m. tonight, about half a day later. So by the time you see the Moon up in the early-morning hours of Wednesday, its terminator will appear not straight but very slightly concave.

And then look for Spica almost a fist and a half to the Moon’s upper right, the four-star pattern of Corvus about the same distance to Spica’s right, and brighter Arcturus three fists or more to the Moon’s upper left.

WEDNESDAY, JANUARY 22

■ The Pleiades and Hyades are the most famous star clusters in Taurus, which is now high overhead and hosting Jupiter. But waiting for your telescope on these moonless evenings are also big, scattered NGC 1746 and NGC 1647 and the smaller “Ugly Ducklings” cluster pair NGC 1807 and NGC 1817. That’s what Ken Hewitt-White names them in his Suburban Stargazer column in the January Sky & Telescope, page 55. Included there are photos and a big chart, with a half dozen notable double stars for small telescopes scattered along the way.

THURSDAY, JANUARY 23

■ Is your sky dark enough for you to see the winter Milky Way? After dinnertime now, it runs vertically from Canis Major low in the southeast, up between Orion and Gemini, through Auriga and Perseus almost straight overhead, and down through Cassiopeia, Cepheus, and Cygnus to the northwest horizon.

■ The Gemini twins lie on their sides these January evenings, left of Orion. Their head stars, Castor and Pollux, are farthest from Orion, one over the other. But Mars now passing them outshines them by far! As shown below.

The Castor figure’s feet are just left of Orion’s very dim Club. Below Gemini’s feet, and lower right of Mars, sparkles Procyon.

FRIDAY, JANUARY 24

■ Mars is still barely more than 2° from Pollux as shown above; it is slowly retrograding westward (toward upper right as seen during evening). After tonight they’ll widen. Keep watch. Mars will reach its western stationary point on February 24th, when will appear just about equidistant (7.2°) from both Pollux and Castor. After that, it will resume its usual eastward (prograde) motion.

SATURDAY, JANUARY 25

■ Orion is now high in the southeast right after dark, and he stands highest and upright due south around 9 p.m. Orion is the brightest of the 88 constellations, but his main pattern is surprisingly small compared to some of his dimmer neighbors. The biggest of these is Eridanus the River to his west (right), enormous but hard to trace. Dimmer Fornax the Furnace, to Eridanus’s lower right, is almost as big as Orion! But its brightest star, Alpha Fornacis, is only magnitude 3.9.

Even the main pattern of Lepus, the Hare cowering under the Hunter’s feet, isn’t much smaller than he is.

Do you know the constellation down below Lepus? It’s a tough one: Columba the Dove, faint, sprawly, and to my eye not a bit dove-like. See the constellation chart in the center of the February Sky & Telescope. Its brightest star, Alpha Columbae or Phact, is a decent magnitude 2.6. To find it, draw a line from Rigel through Beta Leporis (the front of the bunny’s neck) and extend it an equal distance onward.

SUNDAY, JANUARY 26

■ After it’s fully dark, spot the equilateral Winter Triangle in the southeast. Sirius is its brightest and lowest star. Betelgeuse stands above Sirius by about two fists at arm’s length. Left of their midpoint shines Procyon.

Can you discern their colors? Sirius (spectral type A0) is cold white, Betelgeuse (M2) is yellow-orange, and Procyon (F5) is a pale, very slightly yellowish white.

And, standing 4° above Procyon is 3rd-magnitude Gomeisa, Beta Canis Minoris, the only other easy naked-eye star of Canis Minor.

This Week’s Planet Roundup

Mercury is hidden deep in the glow of sunrise.

Venus (magnitude –4.7, near the Aquarius-Pisces border) shines high and bright as the “Evening Star” in the southwest during twilight, then lower in the west-southwest as evening grows late. It sets almost due west about 2½ hours after dark.

As twilight deepens you’ll spot Saturn, much fainter, near Venus. See Saturn below.

In a telescope this week Venus appears about 44% sunlit; its terminator is slightly concave. Venus is enlarging week by week as it swings toward us, while waning in phase as it draws closer to our line of sight to the Sun. It has already grown to about 28 arcseconds from pole to pole. It’ll be almost twice that size by the time it becomes a thin crescent plunging down into the sunset near winter’s end.

Mars is just past its January 15th opposition, glaring at magnitude –1.4 or –1.3. It comes into view in twilight as a steady orange spark low in the east-northeast, like a distant bonfire on a mountaintop. On Friday the 17th it’s in line with Pollux and Castor. It then moves diagonally closer to the two stars, slowly passing Pollux by 2.3° from January 21st through 24th.

Mars shows best in a telescope from late evening through the middle of the night: when it’s very high toward the southeast or south, respectively. Mars remains about 14.5 arcseconds in apparent diameter. It was technically closest to Earth on January 12th. Opposition comes three days later on the 15th. But this is a relatively distant opposition of Mars; it’s near the aphelion of its fairly elliptical orbit, the orbit’s farthest point from the Sun.

A map of the major Martian surface features is in the January Sky & Telescope, page 48, in Bob King’s article “Mars is in Fine Form.” See also Bob’s Mars Extravaganza — Occultation and Opposition Rolled into One! online, which includes a surface-feature map. To find which side of Mars (i.e. which part of the map) will be facing you at the date and time you’ll observe, use our Mars Profiler tool.

Jupiter, a month and a half past its own opposition, shines at a bright magnitude –2.6 in Taurus. It dominates the high south during evening, with fainter Aldebaran (orange), fainter Beta Tauri (bluish white), and the Pleiades nearby. Jupiter is still a good 45 arcseconds wide.

Saturn, magnitude +1.1 in Aquarius, us a spark in the southwest after dark — near brilliant Venus but beginning to pull away from it. The two planets are in conjunction 2.2° apart, on January 18th. By the 24th Saturn is almost 6° below Venus.

Uranus (magnitude 5.7, at the Taurus-Aries border) is very high during evening, 19° west of Jupiter along the ecliptic. You’ll need a good finder chart to tell it from the similar-looking surrounding stars. See last November’s Sky & Telescope, page 49.

Neptune (tougher at magnitude 7.9) is fairly high in the southwest right after dark in the vicinity of Venus and Saturn. Again you’ll need a sufficient finder chart.

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. Both show all 30,000 stars to magnitude 7.6, and 1,500 deep-sky targets — star clusters, nebulae, and galaxies — to search out among them.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many, as well as many more deep-sky objects. It’s currently out of print, but maybe you can find one used.

The next up, once you know your way around well, are the even larger Interstellarum atlas (201,000+ stars to magnitude 9.5, and 14,000 deep-sky objects selected to be detectable by eye in large amateur telescopes), andUranometria 2000.0 (332,000 stars to mag 9.75, and 10,300 deep-sky objects). 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. The pinnacle for total astro-geeks is the new Annals of the Deep Sky series, currently at 11 volumes as it works its way forward through the constellations alphabetically. So far it’s up to H.

Can computerized telescopes replace charts? Not for beginners I don’t think, and not for scopes 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 how to explore the sky. 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 and a curious mind.” Without these, “the sky never becomes a friendly place.”

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn’t simple either. Do learn the essential 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