This week sky at a glance

This Week’s Sky at a Glance, January 15 – 23

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In January, the Moon always steps through Pisces around first quarter.

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Saturn and Venus are drawing apart low in the dawn.

Friday, January 15

• After dinnertime in January, the Great Square of Pegasus balances on one corner high in the west. Tonight the Moon (nearly first-quarter) marks the way by shining to the left of it, as shown here.

The whole Pegasus-Andromeda constellation complex runs all the way from near the zenith (Andromeda’s foot) down through the Great Square (Pegasus’s body) to somewhat low in the west (Pegasus’s nose).

Saturday, January 16

• First-quarter Moon (exact at 6:26 p.m. EST). The Moon shines in dim Pisces upper left of the Great Square of Pegasus, as shown above. Does the half-lit Moon look just a trace bigger than usual? It’s about at perigee.

Sunday, January 17

• If you don’t know Kemble’s Cascade, it’s a lovely binocular asterism in Camelopardalis north of Perseus now high overhead. It’s a straight stream of mostly faint stars 2° long, running northwest to southeast. You can use the finder chart in Gary Seronik’s Binocular Highlight on page 43 of the January Sky & Telescope. Most of its stars are too faint (7th or 8th magnitude) to show on that chart, but the black circle there is centered on its 5th-magnitude middle star.

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As the Moon waxes toward full, it crosses Taurus — and on Tuesday, Aldebaran.

Monday, January 18

• Jupiter’s outer big moon, Callisto, disappears into eclipse by Jupiter’s shadow  slowly, gradually  around 12:32 a.m. Tuesday morning EST; 10:32 p.m. Monday evening MST.

• Bright Capella high overhead, and equally bright Rigel in Orion’s foot, are at almost the same right ascension. This means they cross your sky’s north-south meridian at almost the same time (around 9 or 10 p.m. now, depending on how far east or west you live in your time zone). So whenever Capella passes its very highest, Rigel marks true south over your landscape.

Tuesday, January 19

• The dark limb of the waxing gibbous Moon occults Aldebaran this evening for most of North America. See the time-prediction maps in the January Sky & Telescope, page 49. You can also get local timetables for the star’s disappearance and reappearance. The Moon will be 82% sunlit.

Wednesday, January 20

• Sirius twinkles brightly after dinnertime below Orion in the southeast, far below the Moon. Sometime 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 location, perhaps using a plumb bob or the vertical edge of a building? Sirius leads early in the evening, Betelgeuse leads later.

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Bright Moon shines as the stars come out in the east.

Thursday, January 21

• Tonight the 9.9-magnitude asteroid 115 Thyra will briefly occult a 9.0-magnitude star near the Beehive cluster in Cancer for telescope users along a narrow track from southern New Jersey through the San Diego area. Watch them merge before their combined light suddenly drops by 1.3 magnitudes for up to 7 seconds. Track map, finder charts, time predictions.

Friday, January 22

• The nearly-full Moon shines in Gemini this evening, with Castor and Pollux to its upper left and brighter Procyon to its lower right, as shown here.

• On the other side of the sky, the big Northern Cross of Cygnus plants itself upright on the northwest horizon soon after the end of twilight.

Saturday, January 23

• Full Moon (exact at 8:46 p.m. EST). As the Moon climbs the eastern sky this evening, look for Pollux and Castor above it and Procyon to its right. It’s currently 4° south of the ecliptic; in a telescope, look for features on its northern limb casting extremely thin shadows even at the time of full Moon.

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