This Week’s Sky at a Glance, October 16 – 24

The waxing crescent Moon guides the way to Saturn and Antares in twilight, Oct 16-17, 2015

The waxing crescent Moon guides the way to Saturn and Antares in twilight Friday and Saturday, October 16–17. (The visibility of the faint objects in twilight is exaggerated here. For clarity, the Moon is drawn three times its actual apparent size.)

Moon over Sagittarius, Oct 18-20, 2015

The Moon continues waxing to first quarter over Sagittarius.

Friday, October 16

• The Moon hangs over Saturn and Antares in the southwest at dusk, as shown here.

• This is the time of year when, after nightfall, W-shaped Cassiopeia stands on end halfway up the northeastern sky — and when, off to its left, the dim Little Dipper extends leftward from Polaris in the north.

• Bright Jupiter and fainter Mars pass through conjunction on the mornings of Saturday and Sunday the 17th and 18th, barely 0.4° apart, with brighter Venus blazing close by. See the second-from-last panel far below.

Saturday, October 17

• After dark, spot the W pattern of Cassiopeia standing on end high in northeast. The third segment of the W, counting from the top, points almost straight down. Extend it twice as far down and you're at the Double Cluster in Perseus. This pair of star-swarms is dimly apparent to the unaided eye in a dark sky, and visible in binoculars or a small, wide-field telescope from almost anywhere.

Sunday, October 18

• Look for the little constellation Delphinus about a fist at arm's length upper left of Altair early these evenings. It's a familiar group to scan with binoculars. But did you know about its twin orange variable stars? See Gary Seronik's Binocular Highlight column and chart in the October Sky & Telescope, page 43. And discover some deep telescopic targets in Delphinus with Ken Hewitt-White's Going Deep, page 57.

Monday, October 19

• This is the time of year when the Big Dipper lies horizontal low in the north-northwest in the evening. How low? The farther south you are, the lower. Seen from 40° north (New York, Denver) its bottom stars twinkle nearly 10 degrees up, but at Miami (26° N) the entire Dipper skims beneath the northern horizon.

Tuesday, October 20

• First-quarter Moon (exact at 4:31 p.m. Eastern Daylight Time). The Moon stands in the south at sunset. After dark, look to the Moon's upper left for Alpha and Beta Capricorni, both 3rd magnitude. Alpha, the higher one, is a naked-eye double star (separation 0.1°). Use binoculars to see that Beta is a closer, more unequal double.

• The Orionid meteor shower should be active from midnight to dawn Wednesday and Thursday mornings. It's a middling shower, with about 20 meteors per hour visible before the first light of dawn under ideal dark-sky conditions. The shower's radiant is near the top of Orion's club.

Wednesday, October 21

• Alpha and Beta Cap are now to the Moon's right in early evening.

Thursday, October 22

• Vega is the brightest star very high in the west at dusk. Arcturus, equally bright, is getting low in the west-northwest. The brightest star in the vast region between them, about a third of the way from Arcturus back up toward Vega, is Alphecca, magnitude 2.2 — the crown jewel of Corona Borealis, the Northern Crown.

Friday, October 23

• Have you checked out Mercury, Jupiter, Mars, and Venus in early dawn? The last three of these are in a rapidly evolving dance! Tomorrow morning Venus and Jupiter are 1.6° apart and closing. See the panels below.

Saturday, October 24

• Look upper left of the waxing gibbous Moon this evening for the Great Square of Pegasus balancing on one corner.

• Venus and Jupiter have their conjunction, 1.1° apart, in the dawns of Sunday and Monday.


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.

Pocket Sky Atlas

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's still less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae.

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 once you know your way around, the even larger 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, 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 not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). 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

Jupiter and Mars in conjunction, Oct. 17, 2015

Jupiter and Mars in conjunction, as Venus looks on and Mercury lurks below.

Venus, Jupiter, Mars in a bunch at dawn Oct. 24, 2015

By the 24th, Venus and Jupiter are almost at their October 25–26 conjunction.

Mercury is having a fine dawn apparition. Look for it about 45 minutes before sunrise low in the east. It's far below and perhaps a bit left of Venus, Jupiter, and Mars, as shown here. Mercury brightens slightly from magnitude –0.6 to –0.9 this week.

Venus, Mars, and Jupiter hang together in the east (in Leo) before and during dawn. Venus is the brightest at magnitude –4.6. Jupiter is –1.8, and Mars, much closer to Jupiter, is much fainter at +1.7.

Jupiter and Mars pass through conjunction on Saturday and Sunday the 17th and 18th, just 0.4° apart. After that Jupiter moves upward toward Venus, as shown in the second panel. These two dazzlers are 7° apart on the morning of the 17th but only 1.6° on the 24th. They appear closest, 1.1° apart; on the mornings of the 25th and 26th.

Saturn (magnitude +0.6) sinks away very low in the southwest during twilight. Don't confuse it with orange Antares twinkling 9° to its left or lower left. Binoculars help.

Uranus (magnitude +5.7, in Pisces) and Neptune (magnitude +7.8, in Aquarius) are high in the southeast and south, respectively, by 9 or 10 p.m. Finder charts for Uranus and Neptune.


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 Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.


“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson


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