This Week’s Sky at a Glance

Friday, January 18

  • First-quarter Moon. The Moon is exactly half lit at 6:45 p.m. EST. In early evening, look above the Moon by about about a fist-width at arm's length for the brightest two or three stars of Aries. These are aligned more or less vertically.

    Saturday, January 19

  • In twilight, bright Jupiter comes into view well to the lower left of the Moon. By 8 p.m. things have turned around and Jupiter is shining to the Moon's left or upper left. Closer to the Moon's lower left is the big, dim head of Cetus with its one 2nd-magnitude star, orange Alpha Ceti (Menkar).

    Sunday, January 20

  • The naked-eye eclipsing variable star Algol is at its minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours tonight centered on 12:48 a.m. EST (9:48 p.m. PST.) It takes several additional hours to fade and to rebrighten.

    The waxing gibbous Moon highlights an interesting section of the winter sky. (The Moon symbols are positioned for the middle of North America. They are drawn three times the Moon's actual apparent size.)

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    Monday, January 21

  • Close conjunction of the Moon and Jupiter. Look for a bright "star" unusually near the waxing gibbous Moon this evening, as shown above. The Moon passes less than 1° from it for most of the U.S. and Canada. Think photo opportunity; use a long lens, or zoom to the max. In much of South America the Moon actually occults (covers) Jupiter; timetables.

    Although they look close together, the Moon is only 1.3 light-seconds distant from Earth, while Jupiter is 1,700 times farther away at a distance of 37 light-minutes. See our article Jupiter Dances with the Moon.

    Tuesday, January 22

  • By now the Moon has moved eastward from Jupiter along its orbit to shine well to Jupiter's left after dinnertime, as shown above.

    Look below the Moon for Orion, and far below Orion for brilliant Sirius.

    Wednesday, January 23

  • Week by week, watch the Big Dipper rearing higher up in the northeast as we leave more of winter behind us.

  • Two of Jupiter's moons emerge out of eclipse by Jupiter's shadow tonight: Europa at 7:05 p.m. EST, and Io at 12:16 a.m. EST. With a telescope, watch both swell into view off Jupiter's eastern limb. Meanwhile, Jupiter's Great Red Spot rotates across the planet's centerline around 11:27 p.m. EST.

  • Algol is at its minimum brightness for a couple hours centered on 9:37 p.m. EST.

    Thursday, January 24

  • The bright Moon shines about midway between Betelgeuse in Orion's shoulder to its right, and Pollux in Gemini to the Moon's left. The star above Pollux is Castor. Below the Moon is Procyon in Canis Minor.

    Friday, January 25

  • This evening the Moon shines not quite midway between Procyon to its lower right and Pollux to its upper left.

  • Around 10 p.m. this week (depending on how far east or west you live in your time zone), brilliant Sirius is at its highest due south.

    Sirius is the brightest star in the night sky — and are you far enough south to see the second brightest, Canopus? In one of the many interesting coincidences that devoted skywatchers know about, Canopus lies almost due south of Sirius: by 36°. That's far enough south that it never appears above your horizon unless you're below latitude 37° N (southern Virginia, southern Missouri, central California). And there, you'll need a flat south horizon. Canopus transits the sky's north-south meridian just 21 minutes before Sirius does.

    When to look? Canopus is at its highest point when Beta Canis Majoris — Mirzim, the star a few finger-widths to the right of Sirius — is at its highest point crossing the meridian. Look straight down from Mirzim then.

    Saturday, January 26

  • Full Moon (exact at 11:38 p.m. EST). The Moon is in dim Cancer, with Procyon shining off to its right or upper right during evening, and Pollux and Castor above it.

  • Algol is at its minimum brightness for a couple hours centered on 6:26 p.m. EST. Watch it gradually rebrighten though the course of the evening.


    Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

    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. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,312 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — to hunt among the stars.
    Sky & Telescope

    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope effectively.

    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, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

    Can a computerized telescope replace charts? Not for beginners, I don't think, and certainly not on mounts and tripods that are less than top-quality mechanically (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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 hidden in the glare of the Sun.

    Venus (magnitude –3.9) is just above the southeast horizon about 30 minutes before your local sunrise. It's lower each morning. How much longer can you keep it in view?

    Mars (magnitude +1.2) still glimmers very low in the west-southwest in the fading glow of sunset. Don't confuse it with Fomalhaut far to its left. (On January 24th Mars is at perihelion, its closest to the Sun in its orbit.)

    The white turbulence following Jupiter's Great Red Spot, and unusual amounts of activity in the Equatorial Zone, are evident in this exquisite image taken on January 1st by Christopher Go in the Philippines. South is up.

    Jupiter (magnitude –2.6, in Taurus) is the first "star" to come out high in the southeast after sundown. It dominates the high south after dinnertime, with orange Aldebaran lower left of it and the Pleiades to its upper right. In a telescope, Jupiter is still about 45 arcseconds wide. See our article "Observing Dynamic Jupiter" in the January Sky & Telescope, page 52 — including all of Jupiter's satellite events for January.

    Saturn (magnitude +0.6, in Libra) rises in the east-southeast around 1 a.m. local time. By the beginning of dawn it's fairly high in the south — more or less between Spica, far to its right or upper right, and Antares farther to Saturn's lower left.

    Uranus (magnitude 5.8, in Pisces) is still in view in the southwest right after dark. Finder chart.

    Neptune (magnitude 8.0, in Aquarius) is disappearing into the sunset.


    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) equals Universal Time (also known as UT, UTC, or GMT) minus 5 hours.


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