Special to CosmicTribune.com, September 7, 2025

Excerpts from weekly Sky&Telescope report.

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:

When you face the full Moon and Saturn near its opposition, the Sun is directly behind your head. In late dusk as shown here, that means the Sun is a little below your west horizon.

■ 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 — 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.

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.

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 Dumbbell Nebula, M27. This view is 0.9° wide, about the size of a 60-power field of view in an ordinary telescope eyepiece. North is up, east is left. The star 14 Vulpeculae is magnitude 5.6. The star HD 189733, magnitude 7.7, is a yellow-orange K dwarf 63 light-years away from us, notable for having a hot-Jupiter exoplanet closely orbiting it. The nebula is far in its background, about 1,360 light-years away.

■ 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.

  Sept. 7-14: Focus on M27, the Dumbbell Nebula, The Sky