This Week’s Sky at a Glance, September 19–27

Moon and Jupiter at dawn

Look east at dawn for the waning crescent Moon passing Jupiter, then Regulus.

Friday, September 19

In early dawn Saturday morning, Jupiter shines upper left of the waning Moon in the east, as shown at right. How long has it been since you turned your scope on either Jupiter or the maria-covered waning crescent?

Saturday, September 20

In bright twilight, Mercury and fainter Spica are in conjunction 0.6° apart just above the west-southwest horizon. Use binoculars to scan for them about 20 minutes after sunset.

The eclipsing variable star Algol (Beta Persei) should be at its minimum light, magnitude 3.4 instead of its usual 2.1, for a couple of hours centered on 10:55 p.m. EDT.

In early dawn on Sunday the 21st, the waning crescent Moon shines far below Jupiter and closer to the right of Regulus, as shown above.

Sunday, September 21

Aquila's dark secret: If you're blessed with a really dark sky, try finding the big dark nebula known as "Barnard's E" near Altair in Aquila, using Gary Seronik's Binocular Highlight column and chart in the September Sky & Telescope, page 45.

And if you have a sky that dark, also use binoculars to investigate the big, dim North America Nebula and its surroundings near Deneb in Cygnus using the September issue's Deep-Sky Wonders article, page 56.

Monday, September 22

The September equinox comes at 10:29 p.m. on this date EDT (2:29 September 23rd UT). This is when the Sun crosses the equator heading south for the year. Fall begins in the Northern Hemisphere, spring in the Southern Hemisphere. Day and twilight-plus-night are nearly equal in length. The Sun rises and sets almost exactly east and west.

As summer ends, the Sagittarius Teapot is moves west of due south during evening and tips increasingly far over, as if pouring out the last of summer.

Tuesday, September 23

Arcturus is the bright star fairly high due west at nightfall. It's an orange giant 37 light-years away. Off to its right in the northwest is the Big Dipper, most of whose stars are about 80 light-years away.

Algol is at minimum light again for a couple hours centered on 7:44 p.m. EDT.

Wednesday, September 24

Mars is within 4° of Antares (passing north of it) from this evening through the 30th. Mars is just a little brighter and almost the same color as its namesake star; "Antares" is Greek for "anti-Mars."

Thursday, September 25

With the coming of fall, Deneb slowly replaces Vega as the bright star nearest to the zenith just after nightfall (for mid-northern latitudes).

Friday, September 26

As early as 8 or 9 p.m. now look for Fomalhaut, the lonely 1st-magnitude Autumn Star, twinkling on its way up from the southeast horizon. It will be highest due south around 11 or midnight (depending on your location).

Saturday, September 27

Low in the southwest in twilight, Mars and Antares are passing 3° apart this evening and Sunday evening, as shown below. Meanwhile, off to their right, the waxing crescent Moon floats a couple degrees to the lower right of Saturn (for North America).

Moon passing Saturn, Mars and Antares

The waxing crescent Moon works its way eastward above the star-and-planet display low in the southwestern twilight. (These scenes are plotted for the middle of North America.)

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

Saturn, Mars and Antares at dusk

Follow the Antares-Mars-Saturn lineup as Mars moves leftward from its position here day by day.

Mercury (magnitude 0.0) remains very deep in the sunset. Scan for it with binoculars just above the west-southwest horizon about 20 minutes after sundown. Fainter, twinklier Spica is right nearby. Mercury and Spica appear closest together, 0.6° apart, on Saturday evening the 20th.

Venus (magnitude –3.9) is barely above the horizon due east shortly before sunrise. Bring binoculars.

Mars (magnitude +0.8, in Scorpius) glows low in the southwest at dusk near similarly colored Antares (magnitude 1.0). They'll pass 3° apart on September 27th and 28th.

Jupiter (magnitude –1.9, in Cancer) rises around 3 a.m. and shines brightly in the east before and during dawn. It forms a roughly equilateral triangle with Pollux above it (by about two fists at arm's length) and Procyon to their right. Farther to the right or lower right of Procyon sparkles brighter Sirius.

Saturn (magnitude +0.6, in Libra) is sinking low into the afterglow of sunset. Look for it well to the right of the Mars-Antares pair, and perhaps a little lower depending on your latitude.

Uranus (magnitude 5.7, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are high in the southeast and south, respectively, by 11 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.


2 thoughts on “This Week’s Sky at a Glance, September 19–27

All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.