2025 October 2

Deep Sky Update – September 2025

Callum Potter

September has been a busy month, with the Orkney International Science Festival and the BAA Autumn Meeting occupying the start of the month. It was really nice to welcome so many BAA members to Orkney, and I think everyone had a good time. We’ve had a couple of nice aurorae visible, but missed out on a couple due to cloud. And there have been a few clear nights, though the transparency was not good, and a bit windy. I did manage a session with my Seestar S50 and bagged a few more Messiers. 

I hear that the Kelling Heath Autumn star camp did not have such good skies this year, so not a vintage event, but still very popular. The AstroCamp in Wales went well with some good clear skies at night though marred by very wet days. The Star Gazers Loungers are holding their first camp in a couple of weeks in Somerset – the first they have held for a few years. And the Haw Wood Farm star camp is also in mid-October. So good luck with the weather to anyone heading out to those. Reports are always appreciated.

I am off to the BAA Comet & Meteor Sections meeting in Edinburgh this weekend. Although it is forecast to be a bit windy in Orkney, hopefully it will be less so down south and no travel disruption. Will be great to have a chat with any deep sky observers that are attending.

Section Meeting 2026 – March 28

Preparations for the annual section meeting in 2026 are well underway. The venue is now booked and will be at Dean Close Preparatory School, Cheltenham. Much thanks goes to Cotswold Astronomical Society who are helping to organise the meeting.

I am reaching out to potential speakers, and if you would like to give a talk or short talk please do get in touch.

Tickets should go on sale in the next couple of weeks – check the event page for details as they become available: https://britastro.org/event/deep-sky-section-meeting-2026

Globular Clusters

I am indebted to Mark Stuart who pointed me to this interesting paper on the formation of  globular clusters. I hope you enjoy it too.

https://www.nature.com/articles/s41586-025-09494-x

[And here is a gratuitous image of a globular cluster – M56 taken by me on Sept 24 using my Seestar S50.]

Double Stars for October

This month I move along the Zodiac to Aquarius. Our first double star is Zeta1 Aquarii (STF 2909) is a rather tight double (sep. 2.4 arcseconds), but is made easier by having stars of almost equal magnitude (4.3 and 4.5); the position angle is 152°. It is a binary with a relatively short period of 427 years. It is currently widening and will continue widen for the rest of the 21st century. Zeta1 Aquarii is also fairly close to us, being 28 light years distant. In terms of their spectral type, the two stars are identical, being F2 IV/V. Unsurprisingly, they are usually both observed as being yellow-white. Zeta1 Aquarii is also notable as being the centre of the “Water Jar” (or less poetically the “Mercedes-Benz”) asterism. Moving from the top to the bottom of the constellation, we arrive at 41 Aquarii (H N 56). The separation is easy (5.2 arcseconds) and the magnitudes are not dissimilar (5.6 and 6.7); the position angle is 112°. It is not clear if this is a binary. Their distances from us are similar (A is 241 light years away and B is 239 light years) and they are apparently drifting closer together, so perhaps they are in the process of becoming gravitationally bound, but not yet completely so. The main star is K0 and its companion is F2. I see the colours as yellow and blue and Sissy Haas saw them as peach and pale violet. Moving in the direction of Saturn we come to 94 Aquarii (STF 2998). The magnitudes are similar to 41 Aquarii (5.3 and 7.0), but the separation is wider (12.3 arcseconds); the position angle is 353.2°. It is clearly a binary star, but the orbit has apparently not been calculated although it will be long. Gaia puts them at 73 light years distant, somewhat further out than previous estimates of 69 light years. The spectral types are G8.5 and K2, so not far apart. They have been observed as yellow-white and blue or yellow and orange (which matches the spectral types). Finally, we move in the direction of Diphda (in Cetus) and reach 107 Aquarii (H 2 24). Again, the magnitudes are similar to 41 Aquarii (5.7 and 6.5) and the separation (7.4 arcseconds) lies between 41 Aquarii and 94 Aquarii; the position angle is 135°. This is an optical double. 107 Aquarii A is 202 light years away while B is only 159.5 light years distant. The main star is spectral type A9 whereas B is F2. I see them as yellow and blue (or reddish), but other observers have reported the two stars having similar colours (either as white or yellow pairs). What do you see? 

September Object of Interest

September’s OOI was the Egg Nebula CRL 2688. Many thanks to Alan Thomas, Richard Sargent, Mark Fairfax, Karen Smith, Iain Cartwright, and Jonathon Elliott (who had a few goes at it!).

Here is Richard’s image with a nicely zoomed image of the nebule.

Lee Macdonald was also in touch, and sent a record he made back in 2000. Lee writes: “Not only was this object clearly visible, its light was also strongly polarised. Having read about this polarisation, I tried to see whether it was detectable using a polarising filter that came free with a copy of G. P. Konnen’s book ‘Polarised Light in Nature’. Sure enough, rotating the polarising filter in front of the eyepiece showed substantial brightening and dimming of the nebula at 72x magnification and more so at 107x. At 429x, the nebula appeared bright and slightly fuzzy. It also showed a fainter starlike companion, making it look like a double star.”

I must admit I had not heard about this, and it would be fascinating to see with modern instruments and cameras what the results of this might be. Here is a reference paper that might be interesting to read if you’d like to make a follow-up observation.

Raghvendra, Sahai; et al. (January 1998). “The Structure of the Prototype Bipolar Protoplanetary Nebula CRL 2688 (Egg Nebula): Broadband, Polarimetric, and H2 Line Imaging with NICMOS on the Hubble Space Telescope”. The Astrophysical Journal Letters. 492 (2): L163 – L167. Bibcode:1998ApJ…492L.163S. doi:10.1086/311108

Object of Interest for October

For October our pick for the OOI is IC 10 – one of our local group galaxies which is to be found in Cassiopeia. It is a little faint and diffuse making it a challenge for the visual observer, but those imaging may find it easier. There are areas of star formation that would be nice to capture.

Deep Sky Picture of the Month

There were quite a few images of M33 taken in September, but my pick for this month is that of Dean Ashton who has processed to emphasise the star formation regions.

And Finally

Thanks to everyone that gets in touch – I really enjoy hearing from people about their observing campaigns. And hopefully we get some good observing weather.

Clear, dark skies,

Callum