We have had a more settled period of weather in the last couple of weeks giving some good clear skies. Monday before last (15th May) was one such night and the moon at 3 days past last quarter wasn't due to rise until 02:58 UT. Astronomical twilight was predicted to end at 23:00 UT. I thought I would get some more estimates for the semi-regular variables I monitor in Ursa Major and Draco.
Beginning with Z UMa and using BAA chart 217.02 at 22:15 UT I could see star H which is magnitude 8.7. This was a good indication of my limiting magnitude. I noted at 22:21 UT that Z was brighter than star D (=7.9) and star C (=7.5). In fact, on closer inspection, at 22:31 UT I thought it was pretty close to star B (=7.3) in brightness but perhaps one tenth brighter. This made it B+1 or magnitude 7.2.
Using the same chart I looked at RY UMa. RY was fainter than stars 1 (=6.7), 2 (=7.4) and 4 (=7.7) but not by much for the latter. At 22:50 UT my estimate for RY was one tenth fainter than star 4, i.e. 4-1 or magnitude 7.8.
Moving on to the stars in Draco. Beginning with chart 106.04 and TX Draconis. At 23:04 UT TX was brighter than star N (=7.7) but fainter than star K (=7.0) but not by much. My estimate was that it was 2 points from N and 1 from K, that is K(1)V(2)N or magnitude 7.2.
Finally AH Dra. At 23:11 I noted that AH was fainter than star 1 (=7.0) but at 23:25 I estimated it to be equal to star 2 (=7.3), that is magnitude 7.3.
I think all of these estimates are in reasonable agreement with other observers from the BAA.
All text and images © Duncan Hale-Sutton 2023
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