RW Cephei and CH Cygni (15th January 2024)

We had another cold and clear night here over a week ago on the 15th January. The moon was waxing and three days before first quarter. It lay in the south early in the evening and wasn't due to set until 21:49 UT. Astronomical twilight ended at 18:20. 

My first target of the night was the variable RW Cephei. If you know the constellation of Cepheus, the star is relatively easy to find. The constellation was still relatively high in the sky when I went out to observe about 18:40 UT. The five stars of Cepheus Alpha, Beta, Iota, Xi and Zeta make a sort of cross in the sky and if you look at Zeta it makes a sort of triangular 'foot' with two other stars Delta and Epsilon. RW is to be found on the other side of the foot from the cross. As an aid to finding it, if you look at the binocular chart 312.02 from the BAA the stars P and B and another star of similar brightness make a sort of parallelogram with RW.

At 18:44 UT with 7x50 binoculars I could see that RW was fainter than P (=6.2 mag.). At 18:48 I judged it to be brighter than B (=6.5) but only just. At 18:49 I thought it was much brighter than E (=7.3). Therefore my estimates at 18:48 was P(2)V(1)B i.e. magnitude 6.4.

This is all a bit curious because it seems, relative to other observers at the BAA, I am a bit bright in my estimate yet I am sure that this is what I saw. For example, another observer estimated the brightness to be 7.0 at 18:45 UT on the same day! So we are 0.6 magnitudes apart! Their estimate makes RW 0.3 magnitudes brighter than E and 0.5 magnitudes fainter than B. This seems very at odds with what I recorded. One of the other things I think is strange is that I was very much more aware of the colour of RW (which was red) whereas usually for these stars the colour isn't very obvious at these magnitudes. Hey, ho. I will stick by what I saw.

I moved on to look at the variable CH Cygni in the wing of Cygnus the Swan. This constellation was flying down towards the west and would be difficult to observe in a couple of hours. At 18:58 UT CH was much fainter than star A (=6.5) on chart 089.04 from the BAA and star W (=7.3). At 19:03 I thought it was brighter than star D (=8.0). My estimate at 19:06 was that CH was near to being midway between W and D but slightly nearer to W, that is W(3)V(4)D which is magnitude 7.6.

I am pleased to say that there is no disagreement with this observation and those from other BAA observers on this date!

All text and images © Duncan Hale-Sutton 2024