2025 September 2

Deep Sky Update – August 2025

Sorry for a rather short update this month – rather hectic here getting ready for the Autumn Weekend Meeting, and the Orkney International Science Festival.

Dark nights are returning, and I had my first sighting of the northern lights of the new season last night (1-2 September). And it was quite a nice display, though cloud set in spoiling the view later on.

Many thanks to Peter who sent his double star notes nice and early, and to jim for the September OOI.

Double Stars for September – Peter Morris

This month, I am looking at four doubles in Capricornus. Remarkably they are all in the same north-east to south-west line of seven degrees. Algedi or Alpha Capricorni (STFA 51 AE) is an optical pair of bright stars with a separation of 381.2 arcseconds and the position angle is 290.2. The magnitudes are 3.7 and 4.3 and they are both spectral type G (being G9, the primary is almost K). I see them both as yellow-white.
Directly below Algedi is Dabih or Beta Capricorni. This is a binary despite the wide separation of 205.2 arcseconds and the magnitudes are 3.2 and 6.1; the position angle is 266.4°. The orbital period is said to be 700,000 years. The spectral types are G9 and B9/A0 and not surprisingly I see them as yellow and blue. Continuing down the same line, we reach Rho Capricorni. There is a close binary (SHJ 323) with a separation of 1.7 arcseconds and a position angle of 188.9°. The stars are magnitude 5.0 and 6.7. I was not able to separate them in 2013, but with an orbital period of 376 years the gap is slowly widening. The wider optical pair (SHJ AD) has a separation of 258.7 arcseconds and are magnitude 5.0 and 6.7; the position angle is 149.8°. Their spectral types are F and K and thus displays the usual problem with this type of pairing, I see them as yellow and blue (Sissy Haas sees the secondary
as rose-red). We move a little bit further down this line and arrive at our final double, Omicron Capricorni (SHJ 324). This is a nice easy binary with similar magnitudes of 5.9 and 6.7 and a separation of 22 arcseconds; the position angle is 237.8°. They are both spectral type A. One would expect to see a white pair, but I observed them as lemon yellow and dark yellow while Sissy Haas reports “whitish gold” for both of them. Check them out for yourself.

August Object of Interest

The August target was the open cluster Pismis Moreno 1 and the associated emission nebula Sharpless 2-140 in Cepheus. Many thanks to the observers: Manolo Rodriguez, Alan Thomas, Paul Whitmarsh, Fred Stevenson, Jonathan Elliot and Iain Cartwright. Here is Manolo’s image.

Object of Interest for September

September’s target is The Egg Nebula CRL 2688, actually a protoplanetary nebula in Cygnus. Jim notes that this is an extraordinary object, tiny, but at high power Jimused > 500x) visually revealing two distinct lobes within a nebulous haze. The small angular size might make getting decent images a real challenge.

Deep Sky Picture of the Month

I’ve picked this splendid image of the Cocoon Nebula, IC 5146, by Mike Greenhill-Hooper from France. Amazingly he took the image using a 20″ f/4 Obsession Dobsonian; Paracorr coma corrector
ASI294MM Pro camera with LRGB filters. And exposed 4×150 frame live stacks for each filter; 2s exposure, dark and flats corrected, and aligned, stacked, processed with Affinity Photo and GraXpert.

And Finally

I understand the Kelling Heath autumn equinox star party is coming up soon. I hope there is good observing weather there, and for any members attending, please send me a report.

I hope as September progresses life will calm down a little, and there will be some good observing opportunities.

Clear, dark skies
Callum