This Week’s Sky at a Glance, December 4 – 12 – Sky & Telescope


■ Bright Jupiter and Saturn are nearer collectively now (1.8° aside) than modest, third-magnitude Alpha and Beta Capricorni are above them (2.3° aside), as proven beneath. Wait for full darkish to catch the faint stars. Jupiter and Saturn are closing towards their report-breaking conjunction on December 21st, when they’ll seem solely 0.1° aside. That’s in regards to the width of a toothpick at arm’s size!

Getting nearer… Jupiter and Saturn now seem nearer collectively than Alpha and Beta Capricorni above them.SATURDAY, DECEMBER 5

■ Vega nonetheless shines brightly nicely up within the west-northwest after darkish. The brightest star above it’s Deneb, the top of the large Northern Cross, which is fabricated from the brightest stars of Cygnus. At dusk the shaft of the cross extends decrease left from Deneb. By about 10 p.m., it crops itself kind of upright on the northwest horizon.

■ The waning gibbous Moon rises within the east-northeast round 9 or 10 p.m., near the Sickle of Leo. By daybreak on Sunday morning the sixth the Moon has moved far over to the excessive southwest, as proven beneath.

As daybreak begins to interrupt on Monday the sixth, the waning gibbous Moon kinds a flattish, isosceles triangle with Regulus and orange Algieba (Gamma Leonis) for skywatchers in North America. ■ The eclipsing variable star Algol must be at its minimal brightness, magnitude 3.4 as a substitute of its standard 2.1, for a couple hours centered on 10:43 p.m. EST.


■ This is the time of yr when M31, the Andromeda Galaxy, passes your zenith after dinnertime (if you happen to dwell within the mid-northern latitudes). The actual time depends upon your longitude. Binoculars will present M31 simply off the knee of the Andromeda constellation’s stick determine; see the large night constellation chart within the heart of the December Sky & Telescope.


■ Earliest sundown of the yr, if you happen to dwell close to latitude 40° north. And why is that this, if we’re nonetheless three weeks from the winter solstice? It’s an impact of the lean of Earth’s axis and the eccentricity of Earth’s orbit (TW: historical past and geometry).This offset from the solstice date is balanced out by the alternative taking place at dawn: The Sun would not rise its newest till January 4th.

■ Last-quarter Moon tonight (precisely final quarter at 7:37 p.m. EST). The Moon rises round midnight, beneath the stick-determine star sample of Leo. Once the Moon is nicely up, look to its left for 2nd-magnitude Denebola, Leo’s tail-tip. They’re about 7° aside (for North America).Is this your first sighting of Leo this season? By late winter and spring, Leo can be a landmark of the early-night sky.


■ As the celebrities come out, the Cassiopeia W sample stands on finish (its fainter finish) very excessive within the northeast. Watch Cas flip round to change into a flattened M, increased within the north, later within the night.

■ Algol must be at minimal mild for a couple hours centered on 7:32 p.m. EST.


■ As Cassiopeia rears very excessive within the north-northeast after dusk, the Big Dipper lies shyly down at its lowest due north. It’s totally beneath the north horizon if you happen to’re as far south as Miami.But by midnight the Dipper stands straight up on its deal with in fantastic view within the northeast — whereas Cassiopeia has wheeled right down to the northwest to once more stand on finish (its brighter finish).


■ The Cassiopeia W hangs very excessive within the northeast after darkish. The backside star of the W is Epsilon (ε) Cassiopeiae, the faintest. That’s your place to begin for searching down the little-recognized, little-noticed star cluster Collinder 463: sparse, unfastened, refined, however seen in massive binoculars and vast-subject scopes on these moonless nights. It’s 8° to Epsilon’s celestial north (the course towards Polaris), surrounded by a good quadrilateral of 4th- and fifth-magnitude stars about 3° vast.

The cluster is sort of 1° lengthy, showing curved and quite slim. Its brightest stars are solely eighth and ninth magnitude. Use Chart 1 of the Pocket Sky Atlas.


■ Moon and Venus at daybreak. As day begins to interrupt Saturday morning, look southeast for the skinny crescent Moon with Venus some 4° or 5° to its decrease left (for North America), as proven beneath. Several hours later the Moon will occult Venus in broad daylight for telescope customers within the Pacific time zone. By then the Moon-Venus pair can be getting low within the southwest. Seen from Hawai`i they will be increased in thinner air. See the December Sky & Telescope, web page 50.

The waning Moon within the daybreak passes Venus on Saturday the 12th. SATURDAY, DECEMBER 12

■ Orion comes into view low within the east after dinnertime now, down beneath the Pleiades and Aldebaran. That means Gemini can be arising off to its left (for the world’s mid-northern latitudes). The head stars of the Gemini twins, Castor and Pollux, are at the left finish of the Gemini constellation — one over the opposite, with Castor on high.

■ If you have been out skywatching currently, you have in all probability seen a few Geminid meteors by now! The later you watch the higher. The bathe is because of attain its peak late Sunday night time. For far more on the Geminids see the December Sky & Telescope, web page 14.


This Week’s Planet Roundup

Mercury is misplaced within the glow of dawn.

Venus (magnitude –3.9, in Libra) shines low within the southeast throughout daybreak because the “Morning Star.” It’s a little decrease each week.Very excessive above Venus, and maybe a bit left relying in your latitude, shines Arcturus, pale yellow-orange. Look for fainter Spica much less far to Venus’s higher proper.

Mars (about magnitude –0.9, in Pisces) shines vivid yellow-orange very excessive on the southern facet of the sky throughout night. Mars is fading and shrinking into the space, but it surely’s nonetheless 14 or 13 arcseconds vast in a telescope, sufficiently big to point out floor element throughout regular seeing. It’s gibbous, solely 91% sunlit now from Earth’s viewpoint. The current mud storm exercise could also be dying down, as prompt by the photographs beneath.

Mars on November 21st, imaged by Christopher Go. South is up. The placing darkish diagonal streak at left is a part of Sinus Sabaeus reframed by mud clouds. In the higher heart “the region around Mare Erythaeum is covered with dust,” writes Go. “Even Sinus Meridiani [lower left of center] is shrouded in dust. The eastern part of Sinus Sabeaus is dust free, but the area attached to Meridiani has dust going through! This region of Mars is unrecognizable!”The Syrtis Major facet of Mars as imaged by Go eight days later, on November 29th. South is up. Syrtis Major is the big darkish peninsula pointing down. The darkest horizontal band at proper is Sinus Sabaeus, now trying extra like its regular self. Between Syrtis Major and the South Polar Cap at high, the Hellas Basin is vivid. Dust exercise appears to proceed there.Go lives within the Philippines, on the alternative facet of Earth from North America. Therefore his night observing hours when Mars is excessive are about 12 hours out of sync with ours. Mars additionally rotates about as soon as each 24 hours, so we see the alternative facet of Mars that he does. To get a (dustless) map of the facet of Mars going through you at the date and time you observe, you need to use our Mars Profiler. The map there’s sq.; keep in mind to mentally wrap it onto the facet of a globe. (Features close to the map’s edges change into very foreshortened.)

Jupiter and Saturn (magnitudes –2.Zero and +0.6, respectively) tilt ever farther down within the southwest throughout and after twilight. Look early. Jupiter is the brilliant one; Saturn is higher left of it. Watch their separation shrink from 1.8° to 1.1° this week (from December 4th to 11th). Telescopic views can be disappointing, with the planets low in poor seeing. Jupiter and Saturn will cross simply 0.1° from one another at their conjunction on December 21st, low within the sundown. That’s in regards to the width of a toothpick at arm’s size. The two giants have conjunctions about each 20 years, however this can be their closest one seen in our lifetimes.

Uranus (magnitude 5.7, in Aries) is excessive within the southeast after dusk, about 18° east (decrease left) of Mars. Uranus is just 3.7 arcseconds vast, however that is sufficient to seem as a tiny fuzzy ball, not a level, at excessive energy in even a smallish telescope with sharp optics throughout good seeing. And when you’re there, discover the ninth-magnitude asteroid 8 Flora about 10° south (decrease proper) of Uranus. See Bob King’s Tiny Asteroid Flora and Mighty Uranus Team Up, with finder charts and extra about each.

Neptune (magnitude 7.9, in Aquarius) is equally excessive in early night, over within the south. Neptune is 2.Three arcseconds vast, more durable to resolve than Uranus besides in excellent seeing. Check in on these faint targets while you’re executed with Mars. Or higher but earlier than Mars. Save that vivid night time-imaginative and prescient spoiler for final! Finder charts for Uranus and Neptune.

All descriptions that relate to your horizon — together with the phrases up, down, proper, and left — are written for the world’s mid-northern latitudes. Descriptions that additionally rely upon longitude (primarily Moon positions) are for North America.

Eastern Standard Time, EST, is Universal Time minus 5 hours. (Universal Time is often known as UT, UTC, GMT, or Z time.)

Want to change into a higher astronomer? Learn your means across the constellations. They’re the important thing to finding every thing fainter and deeper to hunt with binoculars or a telescope.

This is an outside nature passion. For a simple-to-use constellation information masking the entire night sky, use the large month-to-month map within the heart of every concern of Sky & Telescope, the important journal of astronomy.

Once you get a telescope, to place it to good use you will want a detailed, massive-scale sky atlas (set of charts). The fundamental normal is the Pocket Sky Atlas (in both the unique or Jumbo Edition), which reveals stars to magnitude 7.6.

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and a whole bunch of telescopic galaxies, star clusters, and nebulae amongst them. Shown right here is the Jumbo Edition, which is in laborious covers and enlarged for simpler studying open air at night time. Sample charts. More in regards to the present editions.Next up is the bigger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; practically 3 times as many. The subsequent up, as soon as you realize your means round, are the even bigger Interstellarum atlas (stars to magnitude 9.5) or Uranometria 2000.0 (stars to magnitude 9.75). And you should definitely learn the way to use sky charts with a telescope.

You’ll additionally need a good deep-sky guidebook, resembling Sky Atlas 2000.0 Companion by Strong and Sinnott, or the larger (and illustrated) Night Sky Observer’s Guide by Kepple and Sanner.

Can a computerized telescope change charts? Not for novices, I do not assume, and never on mounts and tripods which can be lower than high-high quality mechanically, which means heavy and costly. And as Terence Dickinson and Alan Dyer say of 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.”

Audio sky tour. Out below the night sky with yourearbuds in place, hearken to Kelly Beatty’s monthlypodcast tour of the 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


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