TX and AH Draconis

I thought I would have another go at some more variable stars on Monday (the 25th April) to see if I could come up with some more magnitude estimates. The BAA has some other springtime suggestions for beginners with binoculars. I decided to have a go at AH Draconis (AH Dra) which is on chart 106.03. Also on this chart is the variable TX Draconis (TX Dra) which I thought I would do as well. TX Dra is marked in my Atlas and isn't far from Eta Dra. Draco, the Dragon, is a sprawling constellation that sort of encircles the Little Bear, Ursa Minor. At this time of year Draco, which is circumpolar from my latitude, is climbing the sky east of the North Celestial Pole. From the Pole Star, if you draw a line through the first couple of stars of the Little Bear's tail and continue it on towards the east you will come to Eta Dra.

TX Dra is southeast of Eta and forms a sort of pentagonal with four other stars which include the star labelled K on the chart and the variable WW Dra. There are 7 comparison stars labelled R, S, K, T, N, P and U. These seemed a lot more spread out on the chart than the ones for Z and RY UMa. This does make it more difficult to make a comparison between stars as you have to scan across the sky from one star to another. However, I was fortunate that TX was apparently equal in brightness to the star labelled K which is nearby. So at 21:27 UT my estimate of TX's magnitude was 7.0. If you again go to the American Association of Variable Star Observers' website you can plot out the latest estimates of the visual magnitude for this star. Just put in TX Dra into their 'Pick a star' box and 'Plot a light curve'. The Julian Date for the 25th April 2022 at 21:27 is 2459695.39375. You can see that my estimate seems to be pretty good (click on any of the black open circle data points around this date and you will see estimates around this value).

The moon on this date was two days past last quarter and so was not a problem. The sky was quite dark and I could identify star P at 21:13 UT which is magnitude 8.4, so the limiting magnitude for my 8x24 binoculars was fainter than this. I then went on to look at AH Dra. There are some brightish stars nearby which make locating AH relatively easy. These brightish stars form a sort of isosceles triangle with Eta and Nu Dra with these latter stars forming the base. I found the comparison with other stars (labelled 7, 1, 2, 6, 8, 5, and 9) difficult because of their being scattered but at 21:48 UT I thought that AH was roughly equal in brightness to the star labelled 2 which put it at magnitude 7.3. Again by plotting the light curve for this star on the AAVSO website. It is difficult to tell at the moment as their is sparsity of data, but I may be a bit off what other observers are reporting as it was fainter than this.

All text and images © Duncan Hale-Sutton 2022

Mercury and the Pleiades

The BAA has Oberservers' Challenges and at the moment there is one that has been set by John Chuter to photograph the planet Mercury at its greatest elongation in April. Mercury reaches this point on April 29th when it will be within 1.4 degrees of the Pleiades (M45). We had some very nice clear skies two days ago on the 25th April and I thought I would go and see if I could spot the planet. The sun set about 8.15pm BST and I went out to look at the west-northwest horizon about half an hour after this. Initially, I couldn't spot the planet but after going in and coming out again I did see it about 10 degrees above the horizon (a bit more than a fist at arm's length). I began taking a whole series of pictures with my Nikon D90 but the best one was the very last I took at 9.29pm which incorporated the Pleiades nicely:-

I used a Nikkor VR 18-105 f/3.5-5.6 ED lens at 105mm. This was a single shot of 2.5s at f/5.6 ISO 1600. The Pleiades is the star cluster in the upper part of the picture and Mercury is above the tree line in the lower part. 

All text and images © Duncan Hale-Sutton 2022

The Sun on the 21st April 2022

On Thursday I took another picture of the sun using the same set up as I have described in an earlier post. I did make a mistake this time. I had pointed the telescope, as before, using the shadow cast by the sun before taking off the lens cap and improving the focus and alignment. However, I had left the star diagonal, eyepiece and, importantly, the eyepiece cap in place and when I reached down to remove it I had the brief shock of burning on my fingers. The sun, of course, had burnt a neat hole in the eyepiece cap and my fingers had touched molten plastic! It goes to show how careful you need to be. In fact, when I took the eyepiece out to check it over, I noticed that some of the inner plastic support for the lens had been melted, presumably when the sun was off centre. I am beginning to think I may need to stop down the objective lens to reduce the power of the sun's rays.

Anyway, here is my image (taken at 11:07 UT):-

The image has been rotated by 25 degrees so that North is at the top and East is at the left. I have also annotated the image to mark on the designated Active Regions (AR numbers). AR2993 and AR2994 are pretty big areas of sunspots. For example, the single connected region AR2993 is about 32 pixels across in this image whereas the full diameter of the sun is 1065 pixels. The sun is 864,000 miles in diameter and so this area of activity is roughly (32/1065) x 864,000 = 26000 miles across or 3.3 earth diameters! There is a lot of detail here. At full resolution (click on image) you can see that individual areas are made up of lots of much smaller spots.

For comparison, this is Solar Dynamics Observatory image taken on this day (Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams):-

 

You can see how well the two images correlate.

All text and images © Duncan Hale-Sutton 2022 (except for the image from the SDO).

Z and RY Ursae Majoris

Last night (the 20th April) we had a decent clear night and, for the first part of it, the moon was out of the way (it was 4 days past full), so I was determined to see if I could get a magnitude estimate for the variable star Z Ursae Majoris (Z UMa). I have described the approach to this in my previous post. I went out before the end of astronomical twilight (it ended at about 21.20 UT) to get set up and to orientate myself again about the location of this star in Ursa Major. I was using my Opticron 8x24 binoculars again and this time, because the sky was so much darker, I could make out Z UMa and the comparison stars around it. I should, perhaps, have determined what the limiting magnitude was by checking that I could see stars marked as L (magnitude 8.9) and M (magnitude 9.5) but I defintely could make out the small triangle of stars that included H (magnitude 8.7). So the limiting magnitude was fainter than 8.7.

I found that comparing Z UMa with the other stars quite difficult. You have to keep looking at the chart to fix in your minds eye which star is which and then determine which two stars are closest in brightness. I think that my task could be made easier if I invested in some 7x50 binoculars, as the 4 times greater light gathering power would help to brighten up the target and comparison stars (but then they would be heavier). In the end at UT 20:57 I decided that Z UMa was the same brightness as star C which put it at magnitude 7.5. I thought I would try to see if this was in agreement with what other people are recording. If you go to the American Association of Variable Star Observers' website you can plot out the latest estimates of the visual magnitude for this star. Just put in Z UMa into their 'Pick a star' box and 'Plot a light curve'. The Julian Date for the 20th April 2022 at 20:57 is 2459690.37292. You can see that my estimate seems to be spot on (click on any of the black open circle data points around this date and you will see estimates around this value).

On the same chart there is another semi-regular variable star - RY Ursa Majoris (RY UMa) and I decided to try and get an estimate for the magnitude of this star too. There are four comparison stars labelled 1, 2, 4 and 5. I was able to find this star ok and at UT 21:11 I decided that this star was equal in brightness to the star labelled 2 which put it at magnitude 7.4. Again you can look at the AAVSO website for this star and plot a light curve. Using the Julian Date given above this estimate seems to agree well with other observers.

All text and images © Duncan Hale-Sutton 2022

Z Ursae Majoris

I have been reading up about how to go about making visual records of variable stars. The BAA has a variable star section and on their own external website they have some guidance for beginners. Under their beginners page they list some stars for different times of the year that they think might be a good starting point. They also have An Introduction to Variable Star Observing (pdf download) which I found useful to find out how to go about making some basic observations.

So last night I thought I would have a go at seeing if I could at least identify the variable star Z Ursae Majoris (Z UMa). The couple of atlases that I have did show its location in the constellation of Ursa Major. It is near the rear of the bowl of the 'saucepan' asterism towards the stars Megrez and Phad. The nearest bright star to it is Flamsteed 66. The Variable Star Section (VSS) publish finder charts for many variable stars and the one for Z UMa can be found here. On this chart there are a list of comparison stars (labelled A to E, H, L and M) which are used to determine Z UMa's magnitude. So, anyway, armed with this chart, a pair of Opticron 8x24 binoculars and some warm clothes I went out into the garden about 10pm (BST) to see what I could see.

Unfortunately, of course, the moon was one day from full (it is full today, the 16th April) and this meant that the sky was extremely bright and perhaps not that suitable for attempting this! I sat in a tilting chair for comfort and because Ursa Major is virtually overhead at this time. I was quickly able to identify Flamsteed 66 because it is about visual magnitude 5.8 and makes a sort of isosceles triangle with Megrez and Phad. I could also make out Flamsteed 68 (labelled A and magnitude 6.3) near Megrez but could only just make out for sure star B which was magnitude 7.3. As for Z and any of the other stars that were labelled I couldn't see anything but blank sky.

So, anyway, this was a useful exercise. It made it clear that the limiting magnitude for observing stars with these binoculars in a full moon sky was about magnitude 7.3. As for my records I can say that Z UMa was fainter than magnitude 7.3 on the 15th April 2022 between 21:00 and 22:00 UT.

Another thing I did whilst I was looking at Ursa Major was to check the field of view of my 8x24 binoculars. I noticed that with the stars Alioth (delta) and Megrez (epsilon) both visible in the binoculars, the field of view wasn't much larger than these stars angular separation. Alioth has 2000.0 coordinates of RA 12h 15m 25.5s, Dec +57d 01m 57s and Megrez RA 12h 54m 01.7s, Dec +55d 57m 35s. Using a calculator to find their angular separation, it comes out at 5.43 degrees. So the field of view seems to be something like 6 degrees. This seems a bit smaller than the 7.5 degrees marked on the binoculars.

All text and images © Duncan Hale-Sutton 2022

Dr David Gavine

I have only learnt recently of the death of Dr Dave Gavine after seeing his obituary in The Scotsman. He died two years ago in January 2020 aged 82. The last time I saw Dave was when he gave a talk at the Astronomical Society of Edinburgh over 7 years ago when I still lived in Scotland. I recall from that evening that he was sort of hanging up his serious astronomy observing boots as he was giving away his heavy duty boiler suit that he wore when sitting outside on cold evenings. I know Dave was a keen variable star observer and, from what I can remember, liked to carry out visual observations in the old fashioned way using binoculars and telescopes. In fact, having looked up the details of this meeting which took place on the 6th June 2014, Dave had given us a short presentation on variable star observing after the AGM.

Dave Gavine served as president of the ASE from 1983 to 1985 and from 1991 to 1992. I didn't join the ASE until 1994, so this was before my time. However, Dave was, I think editor of the ASE journal at that time, a post he carried out for many years (in fact, Dave started the Journal in August 1980). For his PhD thesis from the Open University, Dave researched into the history of astronomy in Scotland (his thesis title was "Astronomy in Scotland 1745-1900") and, perhaps, my best memories of him were his fascinating talks about the colourful people he had found out about in his astronomy researches. He was a great speaker and he loved to recount an amusing anecdote. He was a great inspiration to all of us.

For this reason (and others), it has encouraged me to join the British Astronomical Society and have a go at submitting some of my own observations. I thought, perhaps, that I would start with doing some variable star work and am now in the process of working out how to go about this.

All text and images © Duncan Hale-Sutton 2022