This Week's Sky at a Glance, January 26 – February 4

By: Alan MacRobert January 26, 2024 0

FRIDAY, JANUARY 26

■ Once it's nice and dark, spot the equilateral Winter Triangle in the southeast. Sparkly Sirius is its brightest and lowest star. Betelgeuse stands above Sirius by about two fists at arm's length. To the left of their midpoint is Procyon. Can you discern their colors? Sirius (spectral type A0) is cold white, Betelgeuse (M2) is yellow-orange, and Procyon (F5) is very slightly on the yellowish side of white. Binoculars make star colors more evident.

■ As Saturday's dawn grows bright, Mercury and fainter Mars have a very difficult conjunction just above the southeast horizon as shown below. You'll need an open horizon in that direction and optical aid, maybe powerful aid.

Mercury-Mars conjunction very low in the dawn, January 27, 2024. — Venus guides the way to the Mercury-Mars conjunction. The visibility of faint objects low in the brightening dawn is exaggerated here.

SATURDAY, JANUARY 27

■ The Moon, two days past full, rises not long after the end of twilight. Once it's well up, spot Regulus to its upper right and Gamma Leonis a little farther to its upper left. These are the two brightest stars of Leo's Sickle.

SUNDAY, JANUARY 28

■ The biggest well-known asterism (informal star pattern) is the Winter Hexagon. It fills the sky toward the east and south these evenings.

Start with brilliant Sirius at its bottom. Going clockwise from there, march up through Procyon, Pollux and Castor, Menkalinan and Capella on high, over and down to Aldebaran, then to Rigel in Orion's foot, and back to Sirius. Betelgeuse shines inside the Hexagon, well off center.

The Hexagon is somewhat distended. But if you draw a line through its middle from Capella down to Sirius, the "Hexagon" is fairly symmetric with respect to that long axis.

Take the line from Aldebaran to Capella, turn it to go from Aldebaran to Betelgeuse instead, and the Winter Hexagon becomes the Heavenly G.

MONDAY, JANUARY 29

■ After dark the Great Square of Pegasus sinks low in the west, balancing on one corner. Meanwhile, the Big Dipper climbs up in the north-northeast, tipping up on its handle.

■ Algol shines at its minimum light, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 6:36 p.m. EST. Watch it rebrighten through the rest of the evening. Comparison-star chart.

TUESDAY, JANUARY 30

■ Orion is high in the southeast right after dark. Left of it is Gemini, headed up by Castor and Pollux at far left. The stick-figure Twins are still lying on their sides.

Well below their legs is bright Procyon. Standing 4° above Procyon is 3rd-magnitude Gomeisa, Beta Canis Minoris, the only other easy naked-eye star of Canis Minor. The Little Dog is seen in profile, but only his topmost outline. Procyon marks his rump, Beta CMi is the back of his neck, and two fainter stars just above that are the top of his head and his nose. Those last two are only 4th and 5th magnitude, respectively. Binoculars help with them through light pollution.

WEDNESDAY, JANUARY 31

■ Have you ever closely compared the colors of Betelgeuse and Aldebaran? Can you detect any difference in their colors at all? I can't, really. Yet Aldebaran, spectral type K5 III, is often called an "orange" giant, while Betelgeuse, spectral type M1-M2 Ia, is usually called a "red" supergiant. Their temperatures are indeed a bit different: 3,900 Kelvin and 3,600 Kelvin, respectively.

A complication: Betelgeuse is brighter, and to the human eye, the colors of bright objects appear, falsely, to be desaturated: looking paler (whiter) than they really are. You can get a slightly better read on the colors of bright stars by defocusing them a bit, to spread their light over a larger area of your retina.

■ L0ok out a southeast window in Thursday's early morning hours for the waning Moon. Near it, in the frigid January night, will be springtime Spica. It's now making its early seasonal appearance in the small hours. See below.

Moon with Spice in the morning hours of Feb. 1, 2024 — The Moon, nearly last quarter, shines near Spica in Thursday's early morning hours. These scenes are drawn exact for an observer near the middle of North America; your Moon positions may differ a bit. Moreover, the Moon is drawn about three times its actual apparent size. On the morning of February 1st it will be about 1° from Spica, or about two Moon diameters.

THURSDAY, FEBRUARY 1

■ Orion is now high in the south-southeast after dinnertime, looking smaller than you may remember him appearing early in the winter when he was low. You're seeing the "Moon illusion" effect. Constellations, not just the Moon, look bigger when they're low.

Under Orion's feet, and to the right of Sirius now, hides Lepus the Hare. Like Canis Major, this is a constellation with a connect-the-dots pattern that really looks like what it's supposed to be. He's a crouching bunny, with his nose pointing lower right, his faint ears extending up toward Rigel (Orion's brighter foot), and his body bunched to the left. His brightest two stars, 3rd-magnitude Alpha and Beta Leporis, form the back and front of his neck.

FRIDAY, FEBRUARY 2

■ Jupiter is three months past its November 2nd opposition, so it's traveling eastward again against the background stars ("direct motion," as opposed to retrograde).

Once the night is fully dark, notice the curved line that Jupiter makes with Alpha Arietis and Alpha Trianguli to the upper right of it, as shown below. That line was nearly straight at the beginning of the year, when Jupiter was at its stationary point. Watch the line grow ever more bent as Jupiter continues eastward against the stars through the rest of the winter.

Jupiter at dusk, early Feb 2024 — Jupiter still shines at a brilliant magnitude –2.4. Alpha Arietis and Alpha Trianguli are upper right of it. At magnitudes 2.0 and 3.0, they are only 1/60 and 1/150 as bright as Jupiter.

■ Last-quarter Moon (exactly so at 6:18 p.m. EST on the 2nd). The Moon rises in the east-southeast around 1 or 2 a.m. Saturday morning. It's below Spica, and three times as far to the lower right of Arcturus.

SATURDAY, FEBRUARY 3

■ Sirius the Dog Star blazes well up in the southeast by midevening. It's the brightest star of Canis Major. In a dark sky with lots of stars visible, the constellation's points can be connected to make a convincing dog seen in profile. He's currently standing on his hind legs. Sirius is on his chest, to the right or lower right of his faint triangular head.

But through the light pollution where most of us live, only his five brightest stars are easily visible. These form the Meat Cleaver. Sirius is the cleaver's top back corner, its blade faces right, and its short handle is down below pointing lower left.

SUNDAY, FEBRUARY 4

Today is the center of winter; we cross the midpoint between the December solstice and the March equinox at 10:16 a.m. EST (15:16 UT). That minute is the very bottom of the wheel of the year, astronomically speaking.

In ancient Gaelic cultures this day was Imbolc: one of the four traditional "cross-quarter" days between the solstices and the equinoxes. The others were May Eve, Lammas, and Halloween, though our calendar has shifted these days a bit from the cross-quarter points since those times.

Groundhog Day (like its German weather-predicting predecessor, Badger Day) was originally the cross-quarter day. But now Groundhog Day is considered to be fixed as February 2nd, avoiding the need for yearly adjustments.

This Week's Planet Roundup

Mercury is dropping out of sight in the glow of sunrise.

Venus, magnitude –4.0, shines in the low southeast during dawn, lower every week.

Mars, magnitude +1.3, is still buried in the sunrise glow.

Jupiter, magnitude –2.4 in Aries, is that bright white dot very high in the south-southwest at nightfall, lower in the southwest later. It sets around midnight. In a telescope Jupiter has shrunk to only 40 or 39 arcseconds wide.

Jupiter with Great Red Spot, Jan. 17, 2024 — Jupiter's Great Red Spot side on January 17th, imaged by Christopher Go. South here is up. Notice the difference in the darkness of the wide South Equatorial Belt on either side of the Red Spot. Go writes that the new hook-like feature just east of the Great Red Spot (to its right here) "is very prominent. This feature seems to be a barrier that prevents the wake of the GRS from spilling to the other side of the SEB."

We've adjusted the contrast to approximate Jupiter's visual appearance. To get a better idea of Jupiter as seen in a telescope at high power, stand far back from your screen and squint a bit.

Saturn, magnitude +1.0 in Aquarius, glimmers low in the west-southwest in twilight. It sets soon after dark.

Uranus, magnitude 5.7 in Aries, lurks in the darkness 12° east (upper left) of Jupiter during evening. In a telescope at high power Uranus is a tiny but distinctly nonstellar ball, 3.7 arcseconds in diameter. Locate and identify it using the finder charts in the November Sky & Telescope, pages 48-49.

Neptune, magnitude 7.9, is getting low in the west-southwest right after dark.

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."

If you do get a computerized scope, make sure the drives can be disengaged so you can swing it around and point it readily by hand rather than only slowly by the electric motors.

However, 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