This Week's Sky at a Glance, September 5 – 14

FRIDAY, SEPTEMBER 5

■ The waxing gibbous Moon shines in the south-southeast this evening, on a line between Altair and Fomalhaut. Altair is the bright star three or four fists above the Moon and maybe somewhat to the right. Fomalhaut, the Autumn Star, rises a little after dark depending on your latitude.

Imagine a line from Altair down through the Moon and continuing on. The line will hit either Fomalhaut or the place on your horizon to watch for it to rise.

SATURDAY, SEPTEMBER 6

■ The bright Moon early this evening forms an isosceles triangle (two equal sides) with Saturn to its lower left and Fomalhaut the same distance to its lower right. At the night advances, the triangle climbs higher and turns clockwise.

SUNDAY, SEPTEMBER 7

■ Full Moon (exactly full at 2:09 p.m. EDT). Saturn follows about 8° or 10° behind it across the sky through the night. By no coincidence, Saturn is just two weeks from its own opposition:

■ With your naked eyes, what is the smallest surface feature that you can see on the Moon? Test your vision with the Lunar Eye Chart on pages 52 and 53 of the September Sky & Telescope. The 12 increasingly difficult test markings were worked out more than a century ago by Harvard astronomer W. H. Pickering.

■ A total eclipse of the Moon will occur for easternmost Africa, most of the Middle East and Asia, and the western half of Australia.

MONDAY, SEPTEMBER 8

■ The two brightest stars of September evenings are Vega high overhead and Arcturus in the west, both magnitude 0.

Draw a line from Vega down to Arcturus. A third of the way down you cross the dim Keystone of Hercules. Two thirds of the way you cross the dim semicircle of Corona Borealis with its one modestly bright star: Alphecca, the gem of the crown.

Just off the Corona semicircle, the recurring nova T Coronae Borealis still has not erupted (see where to check) — yet another testament to the astronomy community's endless eagerness to overpredict exciting but chancy things. T Cor Bor will blow up. . . one of these years. . . eventually. We think.

TUESDAY, SEPTEMBER 9

■ Arcturus, the "Spring Star," shines a little lower in the west after dark every week now. From Arcturus, the narrow, kite-shaped pattern of Boötes extends to the upper right by about two fists at arm's length. The Big Dipper is dipping down to the Kite's right in the northwest.

WEDNESDAY, SEPTEMBER 10

■ "Late summer and early fall are among the most enjoyable seasons for stargazing," writes Matthew Wedel in the September Sky & Telescope. "Nights are getting longer, temperatures are usually not too bad, and there's a lot up there to choose from. ... One of my favorites [is the] globular cluster M2 in Aquarius." At magnitude 6.6 it's visible in a good finderscope under a decent sky. It's easy to locate west of Alpha Aquarii and north of Beta Aquarii if you memorize the shape of the triangle it makes with those two 3rd-magnitude stars. See Matt's chart on page 43.

Just don't be jealous of the Hubble view.

THURSDAY, SEPTEMBER 11

■ How soon after sunset can you make out the big Summer Triangle? As the very first stars come out, Vega, the Triangle's brightest star, is nearly at the zenith (for skywatchers at mid-northern latitudes). The next-brightest of the Triangle is Altair, high in the southeast. Hint: The Moon hangs lower in the southeast at dusk. Look for Altair halfway between it and Vega.

The last of the three Summer Triangle stars is Deneb, the least bright of them, two fists east of Vega.

After dark, of course, they stand out prominently. I can even see them from downtown Boston. As night grows late the Triangle slides toward the west, a preview of what it will do earlier in the evening through the fall.

FRIDAY, SEPTEMBER 12

■ The waning gibbous Moon rises around 10 p.m. daylight-saving time, in Taurus. As it gets higher look for the Pleiades a few degrees to its upper right. Cover the Moon with your finger to make delicate stars near it easier to see.

SATURDAY, SEPTEMBER 13

■ Tonight the last-quarter Moon rises around 11 p.m. It forms an isosceles triangle with bright Capella nearly two fists to its upper right and the Pleiades the same distance to its upper left. A little less far to the Moon's right is Aldebaran. Much closer lower left of the Moon sparkles Beta Tauri.

The Moon becomes precisely last quarter at 6:33 a.m. EDT Sunday morning.

SUNDAY, SEPTEMBER 14

■ Altair is the bright star high towards the south in early evening. Find little Sagitta, the Arrow, barely a fist at arm's length above it. If your light pollution is too bad, use binoculars.

Now imagine rotating the Arrow on its point a third of a turn counterclockwise. Its middle star would now rest almost at at M27, the Dumbbell Nebula. With a total magnitude of 7½, the Dumbbell is a big but subtle gray glow nearly 0.1° wide easily seen in binoculars or a finderscope under a dark sky. In a 4- to 8-inch telescope it's a rectangle or hourglass. It's the brightest planetary nebula in the sky if you sum up all of its spread-out light.

The name Dumbbell Nebula was bestowed by John Herschel in 1828. He was referring to the exercise weights we still call dumbbells, but in his day they were sometimes made by connecting two heavy bells top-to-top by a short rod. The bells were missing their clappers, so they were literally dumb bells. I saw an example once in vintage photos of a gym. It really did look sort of like the nebula's hourglass shape.

A much more recent name for M27, more accurate to modern eyes, is the Applecore Nebula. The earliest use of this name that I find using Google Books is from 1997.

■ The W pattern of Cassiopeia stands on end in the northeast as evening proceeds. Find the W's third segment counting from the top, follow the direction it points down by a little farther than the segment's length, and look for an enhanced, irregular little spot of the Milky Way's glow if you have a dark enough sky. Binoculars will show this to be the Perseus Double Cluster — even through a fair amount of light pollution.

The two clusters of the Double Cluster (NGC 869 and NGC 884) are at very similar distances about 7,600 light-years away.

This Week's Planet Roundup

Mercury is out of sight in conjunction with the Sun.

Venus and Jupiter shine in the east before and during dawn, blazing low at magnitude –3.9 and high at magnitude –2.0, respectively. The gap between them continues to widen by about 1° per day: from 24° apart on Saturday September 6th to 32° a week later on the 13th. Both are about at their farthest from Earth.

Left of Jupiter are the Gemini heads, Castor and Pollux, much fainter.

Mars, a weak magnitude 1.6 in Virgo, still glimmers very low in the west as twilight fades. Use binoculars to try to catch it about 40 minutes after sunset a little above the west-southwest horizon. Twinklier Spica is passing by it this week. They'll appear closest on September 12th, 2¼° apart.

Saturn (magnitude +0.7, in Pisces) is nearing opposition and rises during bright twilight. As the stars come out, find it looming low in the east-southeast. It's lower right of the Great Square of Pegasus, which is standing on one corner, diamond fashion. The lower-left side of the Square points down nearly to Saturn.

The best time to observe Saturn with a telescope is after midnight when it's highest toward the south. We see Saturn's rings almost edge-on this year.

Uranus (magnitude 5.7, in Taurus near the Pleiades) rises around 10 p.m. and gets high in the east in the early morning hours. In a telescope it's a tiny but definitely non-stellar dot 3.6 arcseconds wide.

Neptune, a telescopic "star" at magnitude 7.8, lurks less than 2° north of Saturn. Neptune is just 2.4 arcseconds wide. Use the finder chart for Neptune with respect to Saturn in the September Sky & Telescope, page 49. With a pencil, put a dot on the path of each of the two planets for your date.

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 and graphics that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) is Universal Time minus 4 hours. UT is also known as UTC, GMT, or Z time.

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 a more detailed constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential magazine of astronomy.

For the attitude every amateur astronomer needs, read Jennifer Willis's Modest Expectations Give Rise to Delight.

Once you get a telescope, to put it to good use you'll need a much more detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas, in either the original or Jumbo Edition. Both show all 30,000 stars to magnitude 7.6, and 1,500 deep-sky targets — star clusters, nebulae, and galaxies — to search out among them.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many, as well as many more deep-sky objects. It's currently out of print, but maybe you can find one used.

The next up, once you know your way around well, are the even larger Interstellarum atlas (with 201,000+ stars to magnitude 9.5 and 14,000 deep-sky objects selected to be detectable by eye in large amateur telescopes), and Uranometria 2000.0 (332,000 stars to mag 9.75, and 10,300 deep-sky objects). And read How to Use a Star Chart with a Telescope. It applies just as much to charts on your phone or tablet (which many observers find more versatile) as to charts on paper.

You'll also want a good deep-sky guidebook. A beloved old classic is the three-volume Burnham's Celestial Handbook. An impressive more modern one is the big Night Sky Observer's Guide set (2+ volumes) by Kepple and Sanner. The pinnacle for total astro-geeks is the new Annals of the Deep Sky series, currently at 11 volumes as it works its way forward through the constellations alphabetically. So far it's up to H.

Can computerized telescopes replace charts? Not for beginners I don't think, and not for scopes on mounts and tripods that are less than top-quality mechanically. Unless, that is, you prefer spending your time getting finicky technology to work rather than learning how to explore the sky. 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 and a curious mind." Without these, "the sky never becomes a friendly place."

If you do get a computerized scope, make sure that its drives can be disengaged so you can swing it around and point it readily by hand when you want to, rather than only slowly by the electric motors (which eat batteries).

However, finding faint telescopic objects the old-fashioned way with charts isn't simple either. Do learn the essential tricks at How to Use a Star Chart with a Telescope.

Audio sky tour. Out under the evening sky with your
earbuds in place, listen to Kelly Beatty's monthly
podcast tour of the naked-eye 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; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence."
            — John Adams, 1770