The sky, Jan. 20-26

Special to CosmicTribune.com, January 20, 2025

Excerpts from weekly Sky&Telescope report.

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 has twisted around to the Moon’s upper right, due to your observing platform, the Earth, rotating 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 awaiting 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 by 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.

Mars near Pollux and Castor, Jan. 24, 2025Mars is still just 2½° from Pollux. As a G8 giant star, Pollux is less “red” than Mars; Pollux has a color index (B magnitude minus V magnitude) of +1.00, while Mars is usually listed with a color index of +1.43 (this can vary due to dust storms). But because Mars currently appears 10 times brighter than Pollux, Mars’s color may look more desaturated (mixed with more white) than it really is. Think overexposure.

Compare their colors with your naked eyes, then when they’re brighter in binoculars, and then when much brighter in a medium or large telescope. Color is tricky. Our internal experience of color is a fundamentally different thing than the external reality of it. As is true for everything else in the world.

FRIDAY, JANUARY 24

■ Mars is still barely more than 2° from Pollux as shown above; it is slowly retrograding westward: toward the 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. That’s some bunny.

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.

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