Variable stars TX and AH Draconis, AC Herculis and CH Cygni (19th August 2023)

I have had quite long spell of not being able to do much variable star observing (the last time was at the back end of May). The cause was the poor weather and the light evenings. This month (August) I had an opportunity to get something done on the 19th. The moon was 3 days past new and astronomical twilight ended at 21:40 UT. We had a nice clear sky but I had forgotten how hard it is sometimes to identify where a particular variable is in relation to other stars. It can take as long to refamiliarize myself with a star field as it takes to make the actual magnitude estimate.

I started with TX Draconis which I now know quite well and wasn't too difficult to find. The end two stars of Ursa Minor (Kochab and Pherkad) point to Eta Draconis and the pentangle of stars containing TX are nearby. At 22:03 UT, TX was definitely fainter than star K (at magnitude 7.0, see chart 106.04). At 22:08 UT I couldn't distinguish it in brightness from star N (magnitude 7.7). So that was my estimate. This was in good agreement with other observations by BAA members at this time.

Moving across to AH Draconis which is in the same 9 degree field, at 22:11 UT AH was fainter than star 1 (mag. 7.0) but brighter than star 6 (mag. 7.8). At 22:16 my estimate was that AH was midway between 2 and 6 in brightness, i.e. 2(1)V(1)6 or magnitude 7.6. This may be a little fainter (by 0.2 magnitudes) than other BAA estimates.

I now switched to looking at AC Herculis. This star is not so easy to find. It is located quite a way from the main asterism which forms the body of this greek hero - in fact it is better to draw a line between Delta and Beta Lyrae and continue this south and this will get you close to where AC is found. The nearest bright star is Flamsteed 109 and from there you can hop to the variable. At 22:46 I saw that AC was definitely brighter than star E (mag. 8.2 on chart 048.04) which is right next to it. At 22:48 UT I determined AC was midway in brightness between stars C (=6.9) and star D (=7.4), that is C(1)V(1)D or magnitude 7.2. This was in good agreement with other observations by BAA members.

Finally, I moved on to CH Cygni. This star has the advantage that it can be found near the outstretched wing tip of the swan asterism close to Iota and Kappa Cygni. At 23:10 CH was definitely fainter than star A (magnitude 6.5 on chart 089.04) which is very close by. It was also fainter than star W (=7.3) which is a bit further away. At 23:19 I estimated CH was similar in brightness to star D (=8.0).  Again, this was in good agreement with other observations by BAA members.

All text and images © Duncan Hale-Sutton 2023

How many stars can you see in the Great Square of Pegasus?

The time for the Perseid meteor shower has been and gone (the peak was on the 12/13th August) and I missed out as it was cloudy that night here in Norfolk. The following night at 1.15am BST on the morning of the 14th August I did have a peep outside and was presented with a really clear dark sky that you just don't see that often. Jupiter is now up at this time and it won't be long before it is in our evening sky again. What interested me was just how good the sky transparency was. One of the ways of testing this is to try and see how many stars you can make out with the naked eye within the Great Square of Pegasus which was well placed at this time. This is a good test of your eyesight and a good test of how dark your sky really is. I could see quite a few stars so I decided to spend some time totting them up.

Bob King has described his attempts at doing this in his very good Sky and Telescope article. In the end I counted 9 or 10 and using his list of stars within this asterism I reckon that I was seeing down to magnitude 5.8 which is pretty good.

I used to think we had good dark skies where we are in Norfolk but over recent years I have had to admit that light pollution is getting worse where we are. We have Norwich just about 10 miles away and the lights from this city are getting worse as it expands further out towards the NDR. To the east is Great Yarmouth but that only shows up faintly. Nearby we have some intrusive lights from a local radar station to the north.

When I realistically place our night sky on the Bortle Scale I can see that we are actually approaching a suburban sky (class 5). On better nights we might just be classed as a 4 (rural/suburban transition) but I think that is pushing it as evidenced by the fact that I couldn't see stars fainter than 6th magnitude. I certainly have never seen the Zodiacal Light here and I did try to see M33 with the naked eye but didn't spot it. However, this may be something to try on another dark night. 

All text and images © Duncan Hale-Sutton 2023