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

Observation of the Sun

I thought I would try and do something useful today and so I took a picture of the sun. One way to do this is to use a telescope to project an image onto a white screen. Here is my attempt today:-

This is just a piece of white A4 paper clipped to a book and resting on a chair. The photograph was taken with a mobile phone camera. I used a Celestron NexStar 102 SLT (102mm refractor) with a star diagonal and a 25mm eyepiece to do the projection. The picture was taken at 12:15 GMT. I was quite pleased that the image pretty much undistorted. You can see three sunspots quite clearly in the upper left quadrant of the sun. 

Obviously, it is difficult to point the telescope at the sun because you must not look through the eyepiece or any finder scope. I achieved alignment by looking at the shadow that the scope casts and then, with the star diagonal and eyepiece removed, doing a rough projection onto paper. Once rough alignment had been obtained, I put the diagonal and eyepiece back and used the telescope slewing controls to improve it. I used the 'Solar System Align' functionality of the hand controller to enable the telescope to track the sun. For safety reasons, the sun doesn't appear in the list of solar system objects used for this purpose and you have to go into the 'Utilities Menu' to enable it. 

I have cropped the image a bit so that you can see the solar disk more clearly:-

Here is an image captured today from the Solar Dynamics Observatory (Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams):-

So you can see that the image I have taken corresponds well with the one taken by the SDO. 2976 includes the largest sunspot in this image and the spot to the left of it. 2975 is the much smaller group to the right of it. 2974 is the tiny spot on its own below left of centre.

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

A trio of planets

 

We had a nice showing of three planets the other night about 45 minutes after sunset. Most prominent of these was Venus, the lowest of the three shown in this image taken on the 15th December (at 16:23 GMT). Venus is shining here at roughly magnitude -4.8 and through 8x24 binoculars you could just see the thin crescent of its sunlit side. Venus is approaching inferior conjunction on the 8th January 2022 when it will be between us and the sun. This has not been a good evening showing of the 'Evening Star' this winter due to the position of the ecliptic at this time of year.

The next brightest planet in the photo is Jupiter seen to the upper left. It was shining at magnitude -2.2 and is now beginning to fade from magnitude -2.9 when it was at opposition in August of this year. Between Jupiter and Venus is the much fainter planet Saturn shining at magnitude +0.7.

One of the other reasons I had been keen to look into this area of the sky was to see if I could find comet Leonard. This comet has just had its closest approach to the sun and is now emerging into the evening twilight. On this date the comet was observed to be as bright as 3rd or 4th magnitude and would have been located below and to the right of Venus in this image. Unfortunately, the glare from the setting sun has outshone the comet and, try as I might, I couldn't see it in the image or in binoculars. We might be able to see it climbing into the darkening sky as the days progress towards Christmas.

All text and images © Duncan Hale-Sutton 2021

A beautiful display of Noctilucent Clouds in June

About a week and a half ago on the evening of the 23rd June 2021 we had a beautiful display of Noctilucent Clouds (NLC's). I have written about these night-shining clouds before and we had a display last year about this time but this year's was much more spectacular. I looked out towards the northern horizon about 11pm and I took a number of photos over a period of about half an hour. Here are the best of them (click on any image to obtain an enlarged view):-

These were taken on a Nikon D90 at ISO 800 with exposures of 4 and 5 seconds. The colours of the images have not been altered in any way. The clouds appear as this electric blue. There is certainly quite a bit of structure in the clouds here. The first shows definite banding whilst the second has sort of waves near the television aerial in the foreground. The last is really quite complex.

I think it has been quite a good season for NLC's. You can search for other images on the spaceweathergallery.com.

All text and images © Duncan Hale-Sutton 2021

Partial Solar Eclipse on the 10th June 2021

On Thursday of last week we had a partial solar eclipse as viewed in the UK. The timings for Norwich were for first contact at about 10.11, maximum coverage (around 33%) at 11.17 and last contact at 12.27. All times BST. I decided to set up my Celestron NexStar 102SLT in good time for the beginning of the eclipse and I am glad I did because cloud began to increase after 10am and by about 10.45 we lost all visibility. I decided to project the sun's image onto a screen using a 25mm eyepiece. Initially I didn't include the star diagonal which was a mistake because I couldn't rack the focus far out enough to get a clear image. Once I used the star diagonal everything was fine. I took this image at 10.31 BST:-

This was taken with a Samsung Galaxy A21s phone camera. The 'nibble' out of the sun's image by the moon can clearly be seen. I decided to do a bit more by videoing the image with my phone and putting it live on Facebook. The resultant video can be seen here.

Elsewhere on the earth this was an annular eclipse - the further distance of the moon from the earth meant that its face didn't cover the entirety of sun. The annular eclipse began in northern Canada, moved over the north pole and ended in the far east of Russia.

All text and images © Duncan Hale-Sutton 2021

New Nova in Cassiopeia

On the 18th March this year a new nova was discovered in Cassiopeia by Yuji Nakamura of Japan and was given a designation of V1405 Cas. It was found to be about 1/2 degree south of the open cluster M52 and about 1/2 degree east of the Bubble Nebula (NGC7635). I have been meaning to get around to photographing this 'new star' since I heard the news. Within a few days of its discovery it had brightened from visual magnitude 9.6 to about 8.0 and for about 7 weeks it stayed roughly at that brightness. Then around the 6th May it began to brighten again and it reached a peak of about magnitude 5.3 on the 11th.

This image was taken on the 16th May at about 23.30 BST. I used a Nikon D90 with a 18-105mm lens at 58mm. The exposure time was 15s at ISO 1600. I have adjusted the exposure compensation by +1.0 and binned the image x2. You can click on this image to see a larger view. I have marked the position of the nova.

By the time this image was taken its brightness had dropped from its peak to about 6.6 and since then has continued fall to about 8th magnitude. You can look at a light curve for this object by going to the AAVSO website and typing in V1405 Cas in the text box where its says plot a light curve.

So what is a nova? From an observer's perspective, a nova is the sudden appearance of what looks like a new star where previously there was none to be seen. In actual fact, what we are seeing is a sudden burst of light emitted from a binary star system that was much fainter than was observable. In a classic nova, which I think this is, one of the binary star members is a white dwarf and the other is a main sequence star like our own sun or an evolved star. The orbits of these two stars about their common centre of gravity is very close and tidal forces pull material from the outer layers of the main sequence star into an accretion disc around the white dwarf. A white dwarf is the stellar remnant of a main sequence star and as such, it is compact and very dense. Hydrogen and helium from the accretion disc eventually makes its way to the surface of the white dwarf and when enough of this material collects, a chain reaction of nuclear fusion occurs and the material literally explodes like an H-bomb. The white dwarf suddenly increases in brightness by 50,000 to 100,000 times and ejects material at very fast velocities.

All text and images © Duncan Hale-Sutton 2021