Seven stars in one night (22nd October 2023)

A week last Sunday (the 22nd October) we had some clear weather late in the evening that allowed me to carry out a substantial bit of variable star observing. I think I am getting better at locating the stars in question and then estimating their brightness. One of the tricks of finding the targets is to be able to recognise star patterns and I have made things easier for myself by making some scribbled notes on my location charts. It is helpful to draw in lines between stars that make a shape or pattern. It becomes easier to recognise a shape when you return to it another time. Also, understanding how a chart relates to the wider constellation in which it is found is very helpful when pointing your binoculars in the right direction.

On that Sunday evening there was a bit of light cloud earlier on that was drifting over the sky. The moon was at first quarter and it was due to set at 22:40 UT. Astronomical twilight ended at approximately 18:40 UT.

I began with two variables in Draco on BAA chart 106.04. As usual I was using my 7x50 binoculars. At 22:12 UT TX Draconis (near the star Eta) was brighter than star N (=7.7 mag.). At 22:16 I determined that it was fainter than star K(=7.0) but not by much. My estimate was K(2)V(5)N which made it magnitude 7.2. This is in very good agreement with other observers from the BAA.

On the same chart we have AH Draconis. At 22:27 UT I saw that AH was fainter than star 1 (=7.0 mag.) but not by much. At 22:33 I thought it was equal in brightness to star 2 (=7.3), so my estimate was magnitude 7.3. Again this is in very good agreement with other observers.

Cygnus was still at a reasonable altitude at this time so I switched to observing CH Cygni on chart 089.04. By then most of the light cloud had dissipated. At 22:53 UT I could see that CH was much fainter than star A (=6.5 mag.) on that chart. At 22:56 I felt CH was fainter than star D (=8.0) but not by much. At 22:59 I thought it was brighter than star F (=8.5) and my estimate was D(1)V(4)F, that is magnitude 8.1. CH is an unusual variable star as I have described previously. At the moment it has faded quite a bit since it peaked in brightness between August last year and January this year (it reached about magnitude 6.5). Since June its luminosity does appear to be on the rise again.

I moved on to my next star which was pretty much overhead. This was RW Cephei on chart 312.02. At 23:16 UT RW was fainter than stars P (=6.2) and B (=6.5). At 23:18 I saw that it was brighter than star E (=7.3) but closer to B. My estimate was B(1)V(3)E or magnitude 6.7.

My fifth star to observe that night was GO Pegasi (chart 103.02). At 23:37 UT I found that GO was fainter than star B (=7.0) and brighter than E (=7.8) and my estimate was that it was mid-way between the two, i.e. B(1)V(1)E or magnitude 7.4.

My final two stars were in the constellation of the Great Bear. By midnight (1am BST!) this constellation is rising again in the north east. At 23:55 UT I saw that Z UMa is similar in brightness to star B (=7.3) on chart 217.02. At 23:57 I determined it was brighter than star D (=7.9) and at 23:59 roughly equal to star C (=7.5). So my estimate was magnitude 7.5.

Finally, on the same chart and just creeping into the 23rd October at 00:04 UT I noted that RY UMa was brighter than stars 4 (=7.7) and 5 (=8.3). At 00:06 I estimated that RY was between stars 2 (=7.4) and 1 (=6.7) but closer to 1. My estimate was 1(2)V(5)2 or magnitude 6.9.

All these estimates are in good agreement with other observers from the BAA.

All text and images © Duncan Hale-Sutton 2023

Recent observations of some variable stars

Over the last week we have had a couple of occasions when the sky has been clear enough for a while for me to get out and observe some variable stars. Last Saturday (7th October) I had just long enough to observe GO Pegasi before the murk closed in. That night the moon was 1 day past last quarter and not due to rise until 22:39 UT. Darkness is now falling earlier in the evening and astronomical twilight ended at 19:20 UT on that day. At 21:55 UT there was some hazy cloud around and some parts of the sky were obscured, however, the constellation of Pegasus was pretty clear and I was able to determine that GO was fainter than star B (=7.0 mag.) on BAA chart 103.02 but brighter than star E (=7.8 mag.). It was closer in brightness to star E and my estimate was B(3)V(5)E which made it magnitude 7.3.

This star doesn't have much of a range in magnitude variation (just 0.77 according to the BAAVSS) and, probably because of this, it doesn't appear on the list of beginner's variable stars as described by them. But then there are no beginner binocular variable stars listed in Pegasus, which seems a shame, and this is why I think I picked this one out of the BAAVSS observation program for pulsating stars. I say a shame because Pegasus is well placed at this time of year and is a prominent constellation in the sky. After a recent run of being around magnitude 7.6 it has brightened recently to 7.2 or 7.3 (near the maximum of its range of brightness) and I am glad to say that I am not the only BAA observer to have recorded this! The last time it reached this magnitude was back at the beginning of the year over 280 days ago. This seems a bit odd for a star that supposedly has a period of 79 days! However, I have found a paper by Kate Blackham (pdf) where she can't find any periodicity in this star and has declared it to be an irregular.

Two days ago on the 9th October we had another evening when there was a brief period of clear weather. Again there was quite a bit of hazy cloud and one or two more thicker patches of accumulation. The variable star TX Draconis is now heading down towards the west in the evenings but it is still at a good altitude. At 21:12 UT TX was fainter than star K (=7.0 mag.) on BAA chart 106.04 but brighter than N (=7.7 mag.). My estimate was K(5)V(2)N which made it magnitude 7.5. Another observer at the BAA on the same night estimated it to be visual magnitude 7.3, so we are in reasonable agreement. I had been intending to look at AH Draconis as well but by then a bit of cloud was obscuring my view.

I went on to look at RW Cephei which I have described before. At 21:36 RW was fainter than star P (=6.2 mag.) on chart 312.02 but brighter than star E (=7.3 mag.). My estimate put it midway in brightness between the two, namely B(1)V(1)E making it magnitude 6.9. This star hasn't changed much in brightness by my reckoning since I last looked at it on September 12th. Then I estimated to be 6.8. I think these results are in pretty good agreement with other observations from the BAA and AAVSO.

All text and images © Duncan Hale-Sutton 2023