Estimate Betelgeuse's brightness yourself
Use this photo to estimate Betelgeuse's magnitude using Aldebaran and, with reservations, Bellatrix. Magnitudes are in parentheses. When Bob King took this photo on December 22nd, Betelgeuse was already much more like Bellatrix than Rigel.

Betelgeuse still remains dim. Orion's orange-red supergiant Betelgeuse, always slightly variable, is still in an unusually low dip. As of February 5th it was still V magnitude +1.6 instead of its more typical +0.5. It looks obviously fainter than similarly colored Aldebaran, magnitude +0.9, which it usually outshines.

Orion is high in the southeast to south these evenings. He appears distinctly abnormal with his two shoulders now basically equal. The other shoulder is bluish-white Bellatrix, visual magnitude +1.6, but that's a poor comparison star because of its very different color. As we age our eye lenses yellow, so older people see the world through yellow filters. Therefore your age affects how you judge the brightness of an orange-red star compared to a blue-white one. For instance I'm 68, so I still see Bellatrix looking maybe 0.3 magnitude fainter than Betelgeuse even though their measured V magnitudes are now the same. Read Bob King's The Latest on Betelgeuse

And no, this does not mean Betelgeuse is about to go supernova. It's a massive star "close to the end" of its 10-million-year lifespan — but that's on an astronomical timescale! We'll probably have to wait another 100,000 years or more for Betelgeuse to violently gulp down its core and blaze, for a few weeks, as bright as the full Moon.

Friday, Feb. 7

Venus and Mercury in twilight, early February 2020
Mercury is having an excellent apparition in the dusk far to the lower right of Venus. (The blue 10° scale is about the size of your fist held at arm's length.)

• The nearly full Moon this evening shines below Pollux and Castor and left of Procyon. The bright star farther to the Moon's lower left is Sirius.

• Have you ever closely compared the colors of Betelgeuse and Aldebaran? Can you detect any difference in their colors at all? Normally, when Betelgeuse is the brighter of the two, I can't. But now that Betelgeuse is fainter, to me it looks distinctly redder.

Aldebaran, spectral type K 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: 3,910 Kelvin and 3,590 Kelvin, respectively — and that's when Betelgeuse is normal. As it has dimmed this season its surface has also cooled slightly, by about 100 K.

Most of Betelgeuse's apparent color deepening this winter, however, is due to an illusion in the human eye: The colors of brighter objects appear, falsely, to be desaturated: tending paler (whiter) than they really are.

Saturday, Feb. 8

• Full Supermoon tonight (exactly so at 2:33 a.m. Sunday morning EST). It's "super" because it's only a day and a half from perigee and therefore appears a trace larger than average.

After dark, look for Castor and Pollux high above the Moon, Procyon and then brilliant Sirius way off to the Moon's right, and Regulus below it.

• Algol should be at minimum light for about two hours centered on 9:10 p.m. EST.

Sunday, Feb. 9

• Regulus accompanies the Moon as it climbs the eastern sky this evening. Look roughly 5° to the Moon's right (for North America).

• The sky's biggest asterism is the Winter Hexagon, filling the sky toward the east and south these evenings. Start with brilliant Sirius at its bottom. Going clockwise from there, march right or upper right through Procyon, steeper upper right through Pollux and Castor, up to Menkalinan and then Capella on high, over and down a bit to Aldebaran as you face south, then to Rigel in Orion's foot, and back to Sirius. Betelgeuse shines inside the Hexagon, well off center.

Monday, Feb. 10

• Mercury is at greatest elongation, 18° east of the Sun.

• Sirius the Dog Star, brightest of Canis Major, blazes high in the southeast after dinnertime to the lower left of Orion. Sirius is not only the brightest star (after the Sun), it's also the nearest that's ever visible to the unaided eye from mid-northern latitudes. It's just 8.6 light-years away.

In a dark sky with lots of stars, Canis Major's points can be connected to form a convincing dog profile. He's currently standing on his hind legs; Sirius shines on his chest. But through the light pollution where most of us live, only his five brightest stars are easily visible. These form a short-handled meat cleaver. Sirius is the cleaver's top back corner, its blade faces right, and its handle is down below pointing lower left.

Tuesday, Feb. 11

• The next constellation east of Orion is dim Monoceros the Unicorn, and you probably didn't know that it holds the Fertile Crescent: a ragged double-crescent asterism of binocular stars, about 2° tall, some 10° east of Orion's Belt. See Matt Wedel's Binocular Highlight column and chart in the February Sky & Telescope, page 43.

Wednesday, Feb. 12

• And under the feet of Orion hides Lepus the Hare. Like Canis Major, this is a constellation with a connect-the-dots 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 western foot), and his body bunched to the left. His brightest two stars, 3rd-magnitude Beta and Alpha Leporis, form the front and back of his neck.

Thursday, Feb. 13

• If all you've been doing telescopically with Orion is gaze into the Great Nebula in Orion's Sword, try turning to page 54 in the February Sky & Telescope for a tour of some much lesser-known telescopic sights in Orion's Shield.

Friday, Feb. 14

• By 8 or 9 p.m. now, the Big Dipper stands vertically on its handle in the northeast. In the northwest, Cassiopeia also stands on end at about the same height. Between them is Polaris. The end of winter is in sight.

Saturday, Feb. 15

• Last-quarter Moon (exact at 5:17 p.m. EST.) The Moon rises around 1 or 2 a.m. tonight, with the head of Scorpius following up just below it. By the beginning of dawn Sunday they're higher in the south-southeast. Antares is the brightest star under the Moon and the last to fade out in the oncoming daylight.

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 guide to astronomy.

Jumbo Pocket Sky Atlas cover
The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Sample chart.

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.

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) and Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger 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."

This Week's Planet Roundup

Mercury is having an excellent apparition low in the evening twilight. Look for it about 40 to 60 minutes after sundown, far to the lower right of brilliant Venus (by about 25°). Mercury fades a lot this week, from magnitude –1 to 0, but that's still quite bright.

Venus (magnitude –4.2, in Pisces) is the bright point shining in the southwest during and after twilight. Off to its right or upper right is the Great Square of Pegasus.

In a telescope Venus still appears fairly small (16 arcseconds) and gibbous (70% sunlit). But it will enlarge in size and wane in phase as it remains in the evening sky for the next four months.

Mars (magnitude +1.3, at the Ophiuchus-Sagittarius border) glows in the southeast before and during early dawn. It's moving farther to the left or lower left of Mars-colored Antares, which is about magnitude +1.1. They're 15° to 18° apart this week. Don't bother with a telescope; Mars is still a tiny 5 arcseconds in diameter.

Jupiter (magnitude –1.9, in Sagittarius) is low in the southeast just before and during dawn, well to the lower left of Mars (by about 20°). Nothing else in the vicinity is nearly as bright.

Saturn (magnitude +0.6) is emerging low in the dawn 10° lower left of Jupiter (that's about a fist at arm's length). Binoculars will help.

Uranus (magnitude 5.8, in southwestern Aries) is high in the southwest right after dark.

Neptune (magnitude 7.9, in eastern Aquarius) sinks out of sight right after nightfall, far below Venus. Finder charts for Uranus and Neptune (without Venus).

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 (UT, UTC, GMT, or Z time) minus 5 hours.

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.


Image of Rod


February 8, 2020 at 9:51 pm

mary beth, looking forward to some dark sky reports when you are in NM. For tonight "• Full Supermoon tonight (exactly so at 2:33 a.m. Sunday morning EST)." Here in Maryland it sure is lovely and last night. Clear skies with evening temperature after sunset near 0C. I viewed the rising Moon in the East this evening about 1800 EST along with Venus in WSW, Mercury just below a tree line. Very good unaided views along the ecliptic after sunset, lovely ecliptic and sky. I have the wood burning stove running. In latter January, there were some clear and colder nights with the stove running too. I went outside planning to do some stargazing with my telescopes, and surveyed the winter stars. I came back inside. Sat down in the recliner chair with stove running - my outdoor man adventure and stargazing quickly departed 🙂 When you have no lights around, just large fields and woods, the Moon light is everywhere on a clear, crisp night when the Moon is approaching Full. No snow though, some rain earlier during the week.

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mary beth

February 9, 2020 at 5:51 pm

Hi Rod! The moon was gorgeous here behind the backdrop of the bare winter trees. Fortunately we had clear sky Saturday night but it is cloudy now so won’t get to see the moon tonight. Sounds like a very nice winter scene you have been enjoying! Can you see Canopus?

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February 9, 2020 at 8:01 pm

mary beth, No I cannot see Canopus at my latitude, closer to 39N. Even at transit tonight Canopus will be nearly 1 degree below the horizon. You can see Canopus because we live on a large, round Earth but I cannot 🙂 Looks like clouds moving in here with some rain tomorrow but later in the week, looks to be more clear, colder nights with temps -7C. This morning it was about -5C here. A bit warmer the next few days with day temps near 8-10C with rain, no snow 🙂 However, I will wait and see near the end of the week for some more possible, winter stargazing with the Moon getting out of the night sky. Yes, I will have the wood burning stove running again but this could discourage me from enjoying a clear, cold February night. My outdoor man may take another night off 🙂

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