This Week’s Sky at a Glance, October 17 – 25

Some daily sky sights among the ever-changing stars and planets

Monster sunspot alert — see "This Week's Planet Roundup" below.

Moon passing Jupiter and Regulus at dawn, Oct 17-20, 2014

Watch the thinning crescent Moon pass Jupiter and Regulus in early dawn.

Friday, October 17

Before dawn Saturday morning, Jupiter shines above the waning Moon, as shown at right. Although they look rather close together, Jupiter is 2,100 times farther in the background — it's at a distance of 47 light-minutes, compared to the Moon's 1.3 light-seconds.

Saturday, October 18

This is the time of year when, right 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.

Sunday, October 19

Today the faint Comet Siding Spring (C/2013 A1) makes its much-awaited close pass by Mars, as told in the September Sky & Telescope, page 53, with chart. This will be an extremely challenging observation photographically, and probably impossible visually, with Mars low in the southwest right at the end of twilight and the comet only about 11th or even 12th magnitude, fainter than originally predicted.

At least you can follow a webcast of the encounter courtesy of the Virtual Telescope project; watch in real time starting at 16:45 UT (12:45 p.m. EDT) today, or watch the recording later. And see our article, Comet Siding Spring Skims Past Mars. NASA's fleet of spacecraft at Mars will carry out observations from their much better vantage point.

Monday, October 20

The annual Orionid meteor shower should be active before dawn's first light this morning and for the next few mornings. The shower's radiant (apparent perspective point of origin) is in the top of Orion's Club, and this is highest before morning twilight begins.

Waning crescent Moon and faint Mercury at dawn, Oct. 20-22, 2014

How early in the week can you pick up Mercury in the dawn?

Tuesday, October 21

A challenge observation: as dawn brightens on Wednesday morning the 22nd, binoculars or a telescope may already show Mercury below the thin crescent Moon very low in the east, as shown here. Look about a half hour before sunrise. Mercury is not only low but faint: a tiny crescent only magnitude 2.1. If you succeed, this may be the thinnest you ever see Mercury as a crescent: about 10% sunlit.

Wednesday, October 22

As autumn deepens, the Great Square of Pegasus shines ever higher in the east at nightfall. For now it's still balancing on one corner. Later in the night and the season, it turns to rest upright very high when you face south.

Partial solar eclipse views, Oct. 23, 2014

The farther north and west you are, the deeper Thursday afternoon's partial solar eclipse will become. Click to enlarge image. Credit: Jay Anderson

Thursday, October 23

A partial eclipse of the Sun happens this afternoon for most of North America. Seen from the eastern half of the continent, the Sun sets while the partial eclipse is still in progress. Westerners get to see the whole thing. Eastern New England just misses out. See our article online: Partial Solar Eclipse, October 23, 2014. Griffith Observatory in Los Angeles plans a live webcast from 5:00 to 7:45 p.m. Eastern Daylight Time. Also: webcast from Columbus State University in Georgia, 5 p.m. EDT.

Bonus: The huge sunspot AR2192 should be near the middle of the Sun's disk by today.

While we're at it, here's a preview of the great total solar eclipse that will cross the United States diagonally in less than three years: Americans Will See Total Solar Eclipse in 2017.

Friday, October 24

As the stars come out this week, Deneb is nearly straight overhead for skywatchers at mid-northern latitudes. Brighter Vega is west of the zenith. Altair is farther from the zenith toward the south.

Saturday, October 25

A half hour after sunset, spot the thin waxing crescent Moon very low in the west-southwest. Look to its lower right to see if you can still detect Saturn, which has been sinking lower every day. Binoculars help.

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

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 (able to point with better than 0.2° repeatability, which means fairly 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

Sunspot AR2192

Giant sunspot: Active Region AR2192 on Monday, October 20th, as it rotates into better view. Courtesy NASA / Solar Dynamics Observatory.

The Sun, update Oct. 20: A big naked-eye sunspot has rotated around the Sun's eastern limb into plain view if you have a safe solar filter to view through. (A "naked-eye" sunspot means that no magnification is needed, not no filter!! See Solar Filter Safety.) Active Region AR2192 is still growing; it has enlarged by 1/3 in just the last day. See more at The spot will be wonderfully presented near the middle of the Sun's disk this Thursday the 23rd during the partial solar eclipse Update Oct. 23: The active region has grown bigger and is now right on the Sun's central meridian, just south of the disk's center, perfect timing for today's partial solar eclipse. Here's a photo this morning from the Solar Dynamics Observatory. Photo at sunset from the U.K. Tuesday afternoon. Solar flares remain likely.

Mercury is very dim and low in the dawn for much of the week, but by the 24th or 25th it'll be more readily visible. Look for it above the east-southeast horizon about a half hour before sunrise.

Venus stays hidden in the glare of sunset for another month or so.

Mars (magnitude +0.9) remains low in the southwest during dusk. Use binoculars to took for twinklier orange Antares (magnitude +1.0) ever farther down to Mars's lower right.

Jupiter (magnitude –2.0, at the Cancer-Leo border) rises in the east-northeast around 1 or 2 a.m. It shines brightly high in the east-southeast by dawn. Regulus shines about a fist-width below Jupiter and a bit left.

Saturn (magnitude +0.6, in Libra) is sinking away into the sunset. As twilight fades, use binoculars to look for it far to the right or lower right of Antares — which is far lower right of Mars.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.9, in Aquarius) are high in the southeast and south, respectively, by 9 p.m. See our finder charts for Uranus and Neptune online or in the September Sky & Telescope, page 50.

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, 2014.