The sky, Sept. 22-29: Fall is here

Special to CosmicTribune.com, September 22, 2024

Excerpts from weekly Sky&Telescope report.

SUNDAY, SEPTEMBER 22

■ Goodbye to summer — at last! Today is equinox day. Earth passes the September equinox point in its orbit at 8:44 a.m. EDT (12:44 UT). This is when the Sun, in its six-month journey south, crosses the celestial equator — and equivalently, Earth’s equator. Fall officially begins in the Northern Hemisphere, spring in the Southern Hemisphere.

■ Coincidentally, as if to mark the summer-to-fall transition every year, Deneb is slowly taking over from brighter Vega as the zenith star at nightfall.

MONDAY, SEPTEMBER 23

■ The almost last-quarter Moon rises around 10 or 11 p.m. daylight-saving time. It’ll be exactly last quarter at 2:50 p.m. EDT tomorrow the 24th, halfway between the early-morning hours of tonight and tomorrow night. In the early-morning hours of tonight, the Moon forms a not-quite rectangle with Jupiter and the two much fainter stars Beta and Zeta Tauri, as shown below.

Waning Moon passing Jupiter, Mars, and Gemini, Sept. 24-26, 2024

The waning Moon shines with Jupiter before and during Tuesday’s dawn. Then it passes Mars, then the heads of Gemini, on the next two mornings.

TUESDAY, SEPTEMBER 24

■ The wide W pattern of Cassiopeia is tilting up high in the northeast after dark. Find the W’s third segment counting down from the top. Continue it down by almost twice the segment’s length, and there will be an enhanced 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 waning Moon accompanies Mars before and during Wednesday’s dawn, as shown above.

WEDNESDAY, SEPTEMBER 25

■ The Great Square of Pegasus is high in the east after dark, balancing on one corner.

Running lower left from the Great Square’s left corner is a big line of three 2nd-magnitude stars. These mark the head, backbone and leg of the constellation Andromeda. (The line of three includes the Square’s corner, her head.) Upper left from the foot of this line, you’ll find the Cassiopeia W tilting up.

■ Look east before dawn Thursday morning the 26th, and you’ll find the waning Moon nearly aligned with Castor and Pollux as shown above.

Looking wider, the Moon marks the lower left end of the long, ragged string it makes with Mars, Jupiter, and Aldebaran.

Off to the right of this triangle will be Orion. Below Orion shines searing Sirius.

THURSDAY, SEPTEMBER 26

■ Arcturus shines in the west these evenings after twilight fades out. Capella, equally bright, is barely rising in the north-northeast (depending on your latitude. The farther north you are the higher it will be.) Both stars are magnitude 0.

Later in the evening, sometime around 9 p.m. depending on your location, Arcturus and Capella shine at the same height in their respective compass directions.

When it does, turn around and look low in the south-southeast. There will be 1st-magnitude Fomalhaut at about the same height too — exactly so if you’re at latitude 43° north (Boston, Buffalo, Milwaukee, Boise, Eugene). Seen from south of that latitude, Fomalhaut will appear higher than Capella and Arcturus are. Seen from north of there, it will be lower.

FRIDAY, SEPTEMBER 27

■ This is the time of year when the rich Cygnus Milky Way crosses the zenith about an hour after full dark (for skywatchers at mid-northern latitudes). The Milky Way extends straight up from the south-southwest horizon, passed overhead, and runs straight down to the north-northeast.

SATURDAY, SEPTEMBER 28

■ Cygnus itself floats, swan-like, nearly straight overhead these evenings. Its brightest stars form the big Northern Cross.

When you face southwest and crane your head way, way up, the cross appears to stand upright. It’s about two fists at arm’s length tall, with Deneb as its top. Or to put it another way, when you face southwest the Swan appears to be diving straight down.

■ Step out before or during early dawn Sunday morning the 29th, and look for 1st-magnitude Regulus 2° or 3° to the right of the waning crescent Moon, as shown below.

Waning crescent Moon passing Regulus and Leo at dawn, Sept 28-30, 2024

Leo, an evening constellation of late winter and spring, is already emerging up in the dawn.

SUNDAY, SEPTEMBER 29

■ Face south and look high these evenings after dark. The brightest star there is Altair, the southernmost point of the Summer Triangle. The other two are Deneb and Vega more nearly overhead. A marker for Altair is always its little neighbor Tarazed (Gamma Aquilae), currently a finger-width at arm’s length to Altair’s upper right.

■ Barely a fist at arm’s length above Altair, high look for the faint little constellation Sagitta, the Arrow. The Arrow points toward upper left. If your light pollution hides it, try binoculars. It is 4½° long from tailfeathers to tip, easily fitting into the field of view of most binoculars.

Now imagine rotating the Arrow around its tip a third of a turn counterclockwise. Its middle star would now rest just barely (0.4°) below M27, the big Dumbbell Nebula.

At a total magnitude of 7½, the Dumbbell is a largish 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 its spread-out light. Read all about observing it in Ken Hewitt-White’s Suburban Stargazer column in the September Sky & Telescope, page 55.

Dumbbell Nebula and environs, 0.9 degree field width

The Dumbbell Nebula, M27. This view is 0.9° wide, about the width of the view in an ordinary telescope eyepiece giving 60 power. 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, notable for having a hot-Jupiter exoplanet orbiting it very closely. The nebula is far in its background, about 1,360 light-years away.

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, thick rod. The bells were missing their clappers; they were dumb bells. A much more recent name for M27, more accurate to modern eyes, is the Applecore Nebula. The earliest use of this name I find in Google Books is from 1997.

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