Monday, December 8, 2025

Saturn on the 3rd December 2025

I have been struggling recently to set up my Orion OMC-140 telescope on my HEQ-5 mount. I find that trying to use the polar scope correctly and then carrying out a 3 star setup isn't that easy and it is very time consuming. I had a session the other day where it looked like it was going to be clear and so I began the process in the afternoon of setting up the mount and the telescope. By the time it was dark I had finally carried out a successful 3 star setup but before I could really do anything the whole telescope (and in particular the front corrector of this Maksutov-Cassegrain) had frozen up! It was very disappointing.

So on the 3rd I thought to hell with it, I wouldn't bother with an elaborate setup. I have three slabs set in the ground where I can place the feet of the tripod mount and on these I had marked where I think they should be placed (this at least was a good outcome from the freezing night). So I just set the feet correctly, moved the telescope until it was pointing at Saturn and switched on the equatorial drive (you can do this in one of the hand-controller options). Bingo! It worked very well and I was able to hold Saturn in the eyepiece for over an hour without having to adjust anything.

I decided to draw what I saw through the scope:-

Saturn's rings, at the moment, are virtually edge on. There is a very good application in TheSkyLive which shows where Saturn's moons are and how the rings are displayed to us. I used this information to label the moons that I was able to see. Two other potentially visible moons Mimas and Enceladus were located close to the rings but I was unable to pick them out. I was very pleased to see four of the moons. There was also a hint of a colour change in Saturn which I have indicated by thin line. North is up and east is to the left. The equatorial diameter of Saturn on this day was about 18.9 arc seconds and its magnitude was about 0.75. Our moon was one day from full.

All text and images © Duncan Hale-Sutton 2025 

Sunday, December 7, 2025

Variable Star observations on the 28th November 2025

Just over a week ago the weather tried to play ball and give us some clear conditions but it wasn't that brilliant. The moon was at first quarter and there was light thin high-level cloud that made for poor variable transparency. I had been planning to have a good session of variable star observing with my 10x50 binoculars but in the end I only managed three stars:-

TX Dra, 18.45 UT, chart 106.04, K(5)V(2)N, mag. 7.5
AH Dra, 18.55 UT, chart 106.04, 2(3)V(2)6, mag 7.6
CH Cyg, 19.12 UT, chart 089.04, =H, mag 9.2
 
CH Cygni was very difficult and right at the limit of what I could observe in these conditions. I could only see it in averted vision. Because of the moon and the poor visibility I was worried that these estimates might not be very good, but on comparison with values from other BAA members it seems that they aren't too bad.
 
All text and images © Duncan Hale-Sutton 2025 

 

Thursday, December 4, 2025

Red Aurora on the 3rd December 2025

Last night I unexpectedly had an aurora warning beginning around 18:00 UT with a strength of 380.8 nT on the Aurora Watch magnetometer. Initially, I thought that the moon would be too bright to see anything (it was one day until full) but a friend alerted me to the fact that the aurora was active. The alerts kept coming - the magnetometer at Sumburgh Head recorded 560.2 nT at 19:00 and before falling back to 218.6 nT at 20:00. At around 19:00 UT I was outside with my telescope trained on Saturn when my friend put something up on WhatsApp about what he could see. I turned round and was surprised that I could see a red glow in the north. I went inside to grab my camera and tripod and my first picture was at 19:11 UT:-

You can see red vertical rays through Ursa Major and a little bit of green glow below this. This was taken on a Sony RX100 with an exposure of 4s at f/1.8, ISO1600. The display continued on until 19:21 UT but seemed to be weakening:-

This image was taken at 19:16 UT and I had reduced the shutter speed to 2.5s. The red vertical rays can still be seen but are now at a lower altitude. I took a picture looking more to the north west but there was little evidence of activity in this direction apart from a vague red glow. 

After this I went inside for a bit (it was pretty cold by then and frost was starting to form on the grass). I came out again 30 minutes later at 19:46 to find that the activity had ramped up considerably:-

This was again a 2.5s exposure at f/1.8, ISO1600. There is now a a much more intense general red glow with slanting vertical rays overlaying this. The green glow is at the base of this is still visible. The top of the rays are still lower in altitude than the ones taken at 19:11UT. Looking in the north west the activity had also increased there:-

This was a 2.5s exposure taken at 19:48 UT. The constellation of Lyra is at the extreme left of this image and strong red rays are just seen over the roof top. To the far right a much stronger underlying green glow is evident. At 19:49 I took an image to the north east:-

Not much activity can be made out in this direction and the moon just creeps into the top of the picture. There is some general pink glow to the far left. The display in the north was getting to be very pretty by 19:50 UT:-

 Again a 2.5s exposure. It constantly changed and towards 19:55 UT began to die down again.


 This picture was taken at 19:53 UT.

All text and images © Duncan Hale-Sutton 2025 

Wednesday, November 19, 2025

A Personal tribute to Heather Couper

I wish to pay a personal tribute to the astronomer, broadcaster and writer Dr Heather Couper (2/6/1949 - 19/02/2020) who died five years ago at the relatively young age of 70. She was a great ambassador for astronomy and somebody who took an interest in young people and encouraged them to be astronomers. This was true of myself and, by way of thanks, I want to write down how she influenced me into trying to become a professional astronomer.

When I was at Haileybury College between 1975 and 1980 I gained an interest in astronomy by accident rather than by design. At the school we had a number of different societies to which we could belong and one time, when I was obviously at a bit of a loss as to which one I should join, someone suggested the Astronomical Society. I knew very little about astronomy at that time. I was very science orientated (particularly in physics) but I knew very little about the stars. We were very lucky in those days because the school had an observatory which was equipped with a 4.5 inch refractor (probably a Cooke telescope). This was a splendid old brass instrument, mounted on a pier and contained within a brick building. Here is a picture of me standing outside it when I returned to visit the school in 2000:-

By then it had begun to look as though it had been abandoned. Looking on Google Maps today, the observatory is still there and the dome is in intact but it sits forlornly at the corner of a machinery yard. It makes me wonder if the telescope is still inside.

I was assisted in my learning about astronomy by one of the society members - a Scottish lad who was a five years my senior and who knew how to work the telescope. This was Barry Gardiner who later went on to be an MP and a junior minister in Tony Blair's government. I can still recall him saying to me that I needed to understand about Right Ascension and Declination and showing me a copy of Norton's Star Atlas. This book was probably the prime atlas for amateur astronomers at that time and in 1980, when I won the Powell-Davis Art Prize at school, I asked to be given a copy as a reward (rather than an art book)! So armed with this book and a knowledge of how to use the school telescope I began to explore the skies and after a while I was hooked (I can still remember my first views of objects like Orion Nebula and the impact it had on me).

So, as I progressed through school I remained in the Astronomical Society and as I entered my A-level years I became its secretary. This meant organising meetings of the society and in the summer of 1980 I arranged for an excursion to the Royal Greenwich Observatory in London. Of course I had a lot of help in this from my physics teacher and mentor Ian R Williams (or Doc Williams as he was known). Ian was a superb teacher and very inspiring as he had himself done a PhD in low-temperature physics. You have to understand at this time I was on course to study architecture at Manchester University. I had taken A levels in Physics, Chemistry and Art (yes, I know, an odd combination) and had an offer of a place at Manchester. This had been my direction for a number of years, mainly because I come a family of architects and it seemed like a good profession to go into.

So the day came for a group of us from school and Doc Williams to head into London to the Royal Observatory at Greenwich. We travelled by train, tube and then by boat up river from the center, which was very exciting. In the morning we were to go to the Planetarium and to be treated to a show by one of the lecturers. This is when I met Heather Couper for the first time (she had been appointed senior lecturer there in 1977) and it was Heather who gave us the an excellent planetarium show that entertained us from start to finish. There was always something sparkly about Heather's talks and she always liked to introduce something slightly risqué and in this case it was alluding to how the constellation of Virgo was seen lying low above the horizon at that time of the season. 

At the end of the talk Heather mentioned that she was organising an event for young budding astronomers later in the year and said that if we were interested we could put our names down for it. At the time I didn't think much more about it. We headed off to look round the observatory buildings and then down to the National Maritime Museum (the girls in our group disappeared off shopping in Greenwich!). However, later on when I was back at school I began to feel that I was more interested in astronomy and physics than I was in architecture and one day in dining hall I had this epiphany moment! I was going to do it, I was going to become an astronomer! For the first time in my life I realised what I really wanted to do with my life.

It was quite a turn around and there were a few obstacles to overcome, not least that I needed an A-level in mathematics. I didn't really know how to go about this. My maths skills had been somewhat mediocre up till that point but I had done very well in physics and I knew that I must have it in me somewhere. I went to the careers advisor who turned out to be Mr Bentley who had, by coincidence, been my maths teacher right up until O-level (I famously got 5 out of 95 for one of his maths tests). To his credit, he didn't try to dissuade me and I am grateful to him for not doing this. He laid out a plan for me and said that I would need to go to a college in London (a "crammer" as they were called then) and see if I could get an A-level in mathematics in a year. So this is what I did and went to Davies's College in Southampton Row and a year later I had a grade A maths A-level to add to my tally.

In the mean time I recalled what Heather had said about her event for budding astronomers and I wrote her a long letter telling her about my desire to change career and to come to her one-day meeting. I am forever grateful that she took the time to write back to me and to add me to the list of participants. Later in the year I found my way back into London and attended the day where a number of current astronomers talked about how they had got into this line of work. One of them was Dr Jim Emerson (now emeritus professor) at Queen Mary College, London where eventually I went to study. I can still recall how he said in his talk that it was determination and not necessarily brains that got you where you wanted to be in work.

So, after reapplying to study astronomy at a number of universities, I ended up at Queen Mary College doing a BSc in astrophysics. I continued to see Heather from time to time socially (as she was friends with another student on my course) and she was always encouraging to me and interested in my progress. I was so pleased when she and Nigel Henbest came to my 21st birthday party - it was a real honour to have her there (but then parties were Heather's thing!). My career in astronomy carried on for a number of years until 1992. I left QMC with first class honours and a very good background in mathematics (I had even managed to pass the General Relativity course in the mathematics department). It all went to my head and I tried Part III of the Mathematical Tripos at Cambridge (which had a lot of theory of astrophysics in it) but failed. I picked myself up and dusted myself down and went to do a PhD at Durham University which I finally finished in 1990. My subject was cosmology and the large-scale structure of the universe. I was awarded my PhD and carried on for a couple of years doing research but eventually I found myself in the real world with what my mother would call a proper job in business.

However, my interests in astronomy continue and I will forever be grateful to Heather for being there at the right moment and providing me with the idea that I really could do this and get into the professional world of astronomy. We need more people like her and the other teachers that helped me along my way to inspire and to encourage.


Heather Couper and Nigel Henbest in their garden in Greenwich in about 1983.

All text and images © Duncan Hale-Sutton 2025 

 

Tuesday, November 11, 2025

Comet C/2025 A6 (Lemmon)

We have been fortunate to have several comets grace our skies recently and the brightest of these has been comet Lemmon. This comet was discovered by David Fuls on the 3rd January 2025 during a survey at Mount Lemmon Observatory. During the intervening months it has significantly brightened and around the end of the October it reached its maximum luminosity of about 4th magnitude. On October 25th I was fortunate enough to get a good view of the comet when we had some clear skies in the early evening. At 19:41 UT I took this wide-field view:-

 

The comet has been marked on the image with green lines (the image can be better viewed by clicking on it). It sits in the constellation of Serpens (Caput - i.e. the head) and below the distinctive crown of the constellation of Corona Borealis. The field of view this image is approximately 64x46 degrees. I used a Sony RX100 camera with an exposure of 10s at f/1.8 (ISO 1600). I took another image with the same camera and pointing in the same direction but used a focal length of 20mm rather than 10mm:-

 

This was again a 10s exposure at ISO1600 but this time at f/3.5. The comet has again been marked. Looking closely at this image you can see that the comet tail extends quite a long way up towards the crown of Corona Borealis (some 12 degrees). The field of view of this image is approximately 36x25 degrees.

Finally, I wanted to look at how the comet's position compared with ephemeris predictions. For this I took a chart produced by Nick James at the BAA and overlaid it on my first image that I took:-

 

It was difficult getting the orientation and scaling correct but by making sure that the stars near the comet overlap reasonably well, you can see that the comet does indeed sit on the predicted path. As the observation time was 19:41 UT on the 25th which is 0.820 of the day, you can see that the comet is about the right distance along the track towards the 26th tick mark from the 25th tick mark (taking that the tick marks are for midnight UT).

The comet is now beginning to fade and passed perihelion on the 7th November. 

All text and images © Duncan Hale-Sutton 2025 


 

Wednesday, October 8, 2025

Variable star observations in September 2025

I was able to make some further variable star observations in September. Firstly, on the 13th where the moon was one day before last quarter, I had a go at three stars with my 10x50 binoculars. Twilight ended at about 20:30 UT and the moon rose at 20:27. The skies were clear but the sky transparency was average. Here are my results:-

TX Dra, 20.59 UT, chart 106.04, K(4)V(3)N, mag. 7.4
AH Dra, 21.14 UT, chart 106.04, 2(2)V(3)6, mag 7.5
CH Cyg, 22.03 UT, chart 089.04, F(1)V(6)H, mag 8.6 
 
CH Cygni has been fading quite a bit recently. It is now approaching 9th magnitude, which makes it difficult to measure in smaller aperture binoculars. It may not get any fainter than 9.5.
 
On the 30th September the moon was one day after last quarter and wouldn't set until about 22:03. Twilight ended at 19:45 UT. The skies were clear apart from some cloud in the south west. The sky transparency was again average. I observed TX and AH Draconis again. I also had a go at CH Cygni but I gave up as it was too faint. Here are my results:-
 
TX Dra, 22.22 UT, chart 106.04, K(3)V(4)N, mag. 7.3
AH Dra, 22.34 UT, chart 106.04, 2(2)V(3)6, mag 7.5
 
All my results are in very good agreement with other observers from the BAA.
 
All text and images © Duncan Hale-Sutton 2025 

Thursday, September 11, 2025

Some observations over the summer

It has been a couple of months since I last added anything to this blog. The summer season of twlight filled nights is coming to an end now and I am looking forward to more dark observing sessions in the coming months.

There have been a couple of things to note. On the night of the 12th/13th August I spent half an hour or so looking out for Perseid meteors. It was three days after full moon and so this made the sky pretty bright. However, I did spot five meteors, two of which were significant and left long trails.

Two weeks ago, on the 25th August, I dug out my 10x50 binoculars and did a couple of variable star observations.  This was the last time we had the moon out of the way and on this night it was two days after new moon. Astronomical twilight ended at 21.20 UT. The skies were clear and we had good sky transparency. Using BAA chart 217.02 I made observations of Z and RY UMa:-

Z UMa, 21:37 UT, chart 217.02, D(3)V(2)E, mag. 8.2 
RY UMa, 21:45 UT, chart 217.02, =4,  mag. 7.7
 
Z is beginning to fade rapidly since its peak in May.
 
Finally, on Sunday, the 7th September, there was a total eclipse of the moon. This was always going to be a difficult eclipse to see as the moon wouldn't rise until 18.31 UT and by then a lot of the full eclipse had already happened. As it turned out there was a bank of cloud from our observing location however we did see part of the umbra covering the moon as it rose through a gap in our hedges! This was somewhere between 18:52 and 19:56 UT (19:52 and 20:56 BST). I did try to take a photograph but by the time I got a scope set up, the umbral part of the eclipse was over.
 
All text and images © Duncan Hale-Sutton 2025 

Tuesday, July 1, 2025

Start of the NLC season

Just over a week ago, on the 23rd June 2025, we had our first display of Noctilucent Clouds (NLC) this summer season. I have written about how these high altitude clouds are formed in a previous post. Here is what I saw at just after 11pm BST (22:04 UT):-

This image was taken with a Sony RX100 (1/3s, f/1.8, ISO 1600) and has been cropped so that the cloud features can be seen more clearly (click on the image to obtain the full size version). To the right, near the chimney pot, the head of the constellation of Perseus is rising. The maximum elevation of the clouds is about 16 degrees above the horizon and the display stretches about 49 degrees in azimuth across the sky. I thought that there were three types of cloud present here - type I which is a type of veil, type II which are lines or streaks and type III which appears as a fine herring-bone pattern (this can be seen most clearly to the left of the picture just above the old TV aerial).

It is interesting to me that I have seen these clouds on exactly the same date on 23rd June last year (2024) and the 23rd June 2021. It makes me wonder if this may be the time when these clouds can first be seen in the season. 

A few days later on the 28th June 2025 I saw some more:-

This was not such a good photograph as it was hand held (Sony RX100, 1/2s, f/1.8, ISO 400) but it does show the type III herring-bone pattern at low elevation (much lower than before, the maximum elevation was only about 7 degrees). This was taken a bit later at 22:37 UT.

What is an odd coincidence is that I saw NLC's on the 28th June last year too. Next year I must see if this pattern in dates of appearance repeats again (provided we get some clear weather).

All text and images © Duncan Hale-Sutton 2025 


Monday, June 23, 2025

Orientating an image - a better procedure

Previously, I described a way of orientating an image so that the edges of the frame are parallel to the North-South and East-West directions. In a lot of situations this perhaps does not need to be that accurate but in the case of binary stars where you are trying to determine the position angle (PA) of one star relative to another, then it does become a bit more of an issue. For example, I had been taking some measurements of the separation and PA of the binary star Xi Bootis, and I wondered if my method for orientating the image could be improved. After all, I was using Photoshop and a chart to determine the angle that a line between two field stars made with the horizontal side of the frame. This was potentially inaccurate because I had to place a cursor on where I thought the centre of the field stars were on the chart.

Let me now revisit the problem. Below is the image I took of the binary star after I had rotated it to what I thought was the correct orientation:-

 

As well as the two components of the binary star Xi Boo A and B you can faintly see two field stars in the image. To show this better and get an idea of the problem have a look at the diagram below:-

The field stars have been marked as 1 and 2 and there is a dashed line between them. I have also indicated a dashed line that travels due north from 1 until it meets the line drawn due east from 2. In the situation where the angular distance between field stars 1 and 2 is small (less than a degree or thereabouts) then the right angle triangle approximately lies on a flat plane. Let the angular separation between the two field stars be S. This forms the hypotenuse of the right angled triangle. The vertical dashed line forms the adjacent side to the angle θ marked. This side represents a separation which is the difference in the declinations of the two stars. Let this be δ² - δ¹. It follows from basic trigonometry that the angle θ is to a good approximation θ = arccos (δ² - δ¹ / S).

Now this is all very well but we have to determine the equatorial coordinates of the field stars. If you view the page on the BAA website where observations of Xi Boo have been made you will see that, not only is there a link to In-The-Sky.org, but also a link to the SIMBAD astronomical database for this object. This is a very cool page! If you look near the top of the page there is a 'submit query' button and on the same line just before it there is a field where you can adjust the radius of the search. Changing this radius to 12 arc minutes gives a wider view of the locality round Xi Boo and on the left an image with circled objects. Each of these circled objects (in different colours) relates to a line in the table to the left. If you hover over an object in the image it highlights it in the table (very neat).

This enables us to determine what our field stars are. It turns out that star 1 has a designation of V* EO Boo and star 2 has a designation of BD+19 2872 (they have V magnitudes of 8.43 and 9.06, respectively). Furthermore the table lists the epoch 2000 coordinates of these two stars as RA 14 51 42.2211380760, Dec. +19 05 21.217940052 and RA 14 51 38.0435867520, Dec. +19 10 23.589683616, respectively. I am amazed that they are quoting the accuracy of the positions to 9 decimal places in seconds of arc! Using my routine to calculate the separation of these two stars I find that S = 0.085586862 degrees. Further, δ² - δ¹ can be determined from the stored variables of the program and this corresponds to Z-X. I find that δ² - δ¹ = 0.083992154. Hence  θ = arccos (δ² - δ¹ / S) = 11.07775584 degrees.

If I now compare this value of θ with some measurements of this angle from my image above using Photoshop I get a value of 11.3 degrees, as best as I can determine, so I think I did a pretty good job in orientating my image!

All text and images © Duncan Hale-Sutton 2025
 

Friday, June 20, 2025

Z Ursae Majoris beginning to fade

Just over a week ago, one day after full moon on the 12th June 2025, we had some more clear weather which enabled me to get another view of the variable star Z Ursae Majoris. The twilight at about 22:00 UT (23:00 BST) is now very bright but Z remains pretty much near its peak and so determination of its magnitude is not too much of a problem. Using 10x50 binoculars my estimate was:-

Z UMa, 22:23 UT, chart 217.02, A(1)V(1)B, mag. 6.8

The star is now beginning to fade. At the present time (20th June 2025) it is about 7th magnitude. It looks like the peak in brightness is going to be sharp as I predicted but it may yet brighten again or slow down its fade. We shall see!

All text and images © Duncan Hale-Sutton 2025 

Sunday, June 8, 2025

Z Ursae Majoris on the 30th May 2025

The recent weather has been far too cloudy for me to carry out any observations but, just over a week ago, on the 30th May I was able to make an observation of Z Uma. Even then the weather wasn't that clear as I had to observe through thin cloud. At that time the moon was 3 days after new and twilight was an issue as it always is in the middle of summer. My estimate was as follows:-

Z UMa, 22:20 UT, chart 217.02, A(3)V(7)B, mag. 6.6

From this observation it looks like Z is beginning to fade after its recent maximum. Looking at other data from the BAA, this now does seem to be the case.

All text and images © Duncan Hale-Sutton 2025 

Sunday, June 1, 2025

Using a program to calculate the angular separation of Mizar and Alcor

In my last post I described a program that could be used to calculate the angular separation of two celestial objects using their equatorial coordinates. I now want to revisit my calculation of the separation of the double stars Mizar and Alcor. I previously gave the coordinates of Mizar A as RA 13h 23m 55.543s Dec. +54 deg. 55' 31.30" and Alcor as RA 13h 25m 13.538s Dec. +54 deg. 59' 16.65". I previously found that their separation to 4 decimal places was 0.1968 degrees. Now using my own program I find that inputting the same coordinates I get the separation as 0.196820915 degrees which to four decimal places is the same value as before.

Unfortunately, as often happens on the web, the tool that I used previously to calculate the separation of these two stars is no longer accessible and so I can't compare the values to higher decimal places.

However I have found some other online calculators. For example, inputting these coordinates in  Clear Sky Tonight I obtain the separation as 11 minutes and 48.56 seconds which corresponds to 0.196822222 in decimal degrees and this differs from mine at the 6th decimal place. Another online calculator is this one by the Russian-Turkish 1.5m telescope. If I enter the coordinates here I get a separation of 0.196837 degrees which differs from mine at the 5th decimal place.

To be honest, this is more than I expected, so rounding obviously is an issue. However, 1 arc second is 0.00028 degrees so we are talking about a tenth of an arc second error or so at most.

All text and images © Duncan Hale-Sutton 2025

 

A program to calculate the angular separation between two stars

I have previously written a program to calculate binary star orbits using the algorithm given in Practical Astronomy with your Calculator by Peter Duffet-Smith. I wrote the code for a programmable calculator (a Casio fx-4500P) and it makes predicting the positions of binary stars fairly straight forward. Recently I had been thinking it would be useful to have some code that could calculate the angular separation of any two stars (or any two celestial objects) as this is something that is always cropping up. For example, in May last year I took a photograph of the double star Mizar and Alcor and I used their angular separation to determine the resolution of my camera (in arc seconds per pixel) when it was at the prime focus of my Orion OMC-140 telescope.

So now I have used another algorithm in Peter's book to write some code for the Casio to do this (see section (31) on page 52). It is based on knowing the equatorial coordinates of the two objects (in other words their Right Ascension and Declination):-

"STAR 1"
Pause 3
A"H": B"M": C"S"
W = A + B/60 + C/3600
E"D": F"M": G"S"
X = E + F/60 + G/3600
D"SIGN +/-1"
D = -1 → X = XD ∆
"STAR 2"
Pause 3
H"H": I"M": J"S"
Y = H + I/60 + J/3600
L"D": M"M": N"S"
Z = L + M/60 + N/3600
K"SIGN (+/-1)"
K = -1 → Z = ZK ∆
U = 15(W - Y) 
S = cosˉ¹ (sin X x sin Z + cos X x cos Z x cos U) ▲
S > 0.1 → Goto 1 ∆
"RECALC"
Pause 3
T =  √((cos X x U)² + (X - Z)²) ▲
Lbl 1
 
Before running this program it is best to set the mode to degrees and to clear the memories. The Right Ascension coordinates of the two objects are entered in the hours, minutes, seconds format and for the Declination in degrees, minutes, seconds. The angular separation of the two objects, S, is given in decimal degrees.
 
Further execution of the program is possible for small angles (less than 0.1 of a degree). This is because there may be a limitation in the accuracy of the calculator to return an exact result due to its precision. T gives an alternative calculation of the angular separation which may be more accurate. 

All text and images © Duncan Hale-Sutton 2025

Saturday, May 24, 2025

Z Ursae Majoris still exceptionally bright

Four days ago on the 20th May 2025 we had a clear evening here in Norfolk and I was again able to observe the long-period variable Z UMa. The moon was at last quarter and wouldn't rise until 01.38 UT on the 21st, however, it is now technically twilight all night. The skies were clear and the transparency was good but with some thin cloud in places.

Z was still bright and has not declined yet. In fact, I think it has increased in brightness again compared to my last estimate. This was what I saw with 7x50 binoculars:-

Z UMa, 22:27 UT, chart 217.02, =A, mag. 6.3

It seems that people at the BAA have finally woken up to the fact that Z appears to be exceptionally bright as John Toone sent out an alert yesterday that said "Since mid-May I have had Z UMa at 6.2mv, slightly brighter than comp star A. This is the brightest I have seen it since commencing monitoring in 1978."
 
All text and images © Duncan Hale-Sutton 2025

Tuesday, May 20, 2025

More variable star observations

A week ago (the 13th May 2025) we again had some very clear weather (the story of this spring here in the east of England) and I was able to get a few more estimates for some long-period variable stars even though the moon was one day after full and astronomical twilight didn't end until nearly midnight (23.45 BST). Here are my observations (using 10x50 binoculars):-

Z UMa, 21:52 UT, chart 217.02, A(1)V(4)B, mag. 6.5
RY UMa 22.09 UT, chart 217.02, 1(5)V(2)2, mag. 7.2
TX Dra, 22.25 UT, chart 106.04, K(5)V(2)N, mag. 7.5
AH Dra, 22.29 UT, chart 106.04, 1(1)V(2)2, mag 7.1 

The star Z UMa remains very bright and close to its maximum. There is no sign yet (as of May 20th) that its brightness is declining.
 
All text and images © Duncan Hale-Sutton 2025

Friday, May 16, 2025

More about Z Ursae Majoris

In the last week I have added another item on the BAA Forum about this star under the heading "What's happening to Z Ursae Majoris?". This is what I said:-

"You might have noticed that Z UMa has just recently reached a peak in its brightness and this peak was brighter than previous peaks for the last four years (see the attached screen shot from the BAAVSS database). I am going to stick my neck out here and make a bit of a prediction! I think we will see more of this in the next four years with more sharply defined peaks and troughs and a wider range in magnitudes. My reasoning is the interplay between the two periods of pulsation that this star shows. If you look back to 2016-2017 there was a period then when the amplitude of variation died away somewhat and there was evidence for double peaks in the pulsation prior to this. Then the variation recovered and there were more sharply defined peaks and troughs. I think we are now seeing a repeat of this behaviour.

Why do I think this? Well, I am not sure I believe that the second, less prominent, pulsation period in this star is dying away. I think that this modulation of the amplitude and the double peaks (see above) is evidence that the two pulsation periods in this star are still operating together and causing the modulations to the primary pulsation period that we see. Over the next four years we will probably see these sharply defined peaks because the two periods are acting in concert and then after this they will go out of phase and we will see the return of the double peaks and the lower amplitude range. We shall see! For more on this read my previous posts on this subject."

Well, interestingly my post elicited no response from other members at the BAA at all and sometimes I think I am just talking to myself. It is difficult to know whether they find what I am saying is interesting or whether they just think it is boring, or perhaps worse still, they think I am wrong but they are too polite to say! I will be interested to see if my prediction turns out to be true. If it is I think that John Greaves may be wrong in suggesting that the two periods of pulsation in this star are unifying to one and that it may be premature to say that this star is becoming more Mira like.

One of the projects I am thinking about starting is to see if I can process this data for myself. It will involve me trying to learn a new computer language like Python but I may try and see if I can use AI to construct it to save some time. The first job would be to bin up this data and see how well defined it is. For example, it may be easier to see how frequently the double peaks occur as I reckon these are indicative of dual periods in the pulsation. Watch this space!

All text and images © Duncan Hale-Sutton 2025 (except the images kindly provided by the BAA).

 

Saturday, May 10, 2025

What I know about Z Ursae Majoris

 

This pulsating variable star does interest me and, as it is well observed, there are aspects to its displayed behaviour that I find intriguing. I have discussed this star before but here I wanted to record some of the things I have said about it on the BAA discussion forum.

Firstly, on the 15th June 2022 I asked the following (under the title "What's happening to Z Ursae Majoris?"):-

"I am a new member of the BAA and new to variable star observing. Like many others, I am sure, I have begun a few observations of Z UMa and to find out a bit more about this star I have been doing a bit of reading up. One of the most interesting papers was by John Greaves in the VSS Circular 184 (pdf download). What got my attention was that over the last 50 years or so John has determined that this star’s period of pulsation has been changing. If I have got this right, based on BAA data prior to 1995 there were two contributing pulsation periods – one main one of 194.0 days and one less significant one of 204.8 days. After 1995 the period has settled down to 189.0 days and there is no evidence for the less significant period. What’s more after 2006 the visual magnitude range of variations in this star has increased to about 2.8 magnitudes. John concluded that the period and magnitude range change are making this star more like a Mira variable rather than a semiregular.

So what is causing these changes? What physical changes within the star are causing it to evolve? There is another paper in the literature that I found Secular Evolution in Mira Variable Pulsations which looked at the changes in the period of 547 Mira variables and for about 10 percent of the sample statistically significant long-term period changes were seen. Templeton and Mattei believe that changes could be caused by thermal pulses (which I take it are caused by flashes of nuclear burning in the core?). However, another possible reason that they consider for evolutionary changes in the period is non-linear behaviour in the physics of the pulsation mechanism.

I am interested to know what other people understand about the evolution of these giant stars and whether other semiregular stars are showing signs period change."

On the 3rd July 2022 I put up another post under the same topic heading:-

 "Another aspect of the light curve of this star that interested me was that from time-to-time the maxima appear to be double peaked. This has been shown nicely by some recent observations using CMOS detectors (see figure below which has been produced from the BAA database). If you look at the light curve after the 1st Jan 2022 you can see (green data points) that Z UMa reached a maximum of about magnitude 6.6 around the 14th March, then it faded a bit to about 7.7 around the 21st April before brightening again to about magnitude 6.8 around the 22nd May (roughly 69 days from peak-to-peak). The same double peak is seen in the visual data (black circles) but the scatter in the CMOS data is much tighter. Looking back at the four maxima prior to this the visual data (black circles) hint that this double peaked behaviour has been been developing as time progresses.

If you go back further in time other reasonably clear examples of a double peak can be seen in August 2016, January 2008 to July 2009, January 1999, July 1999 and July 1995 (I haven’t gone back further than this). So what is causing this? One suggestion has been that this is due to the interaction of different pulsation cycles within the star but this is not so easy to understand if, as John Greaves says (see my first post), after 1995 there is virtually only one pulsation period of 189 days. With more people carrying out observations using more accurate electronic detectors it will be interesting to see how often this double peaked behaviour appears."

Finally, on the 31st March 2023 I added another item under this heading:-

"I was pleased to see that Z UMa has been highlighted in a recent facebook post. I have added the light curve of this variable star from this post below. As described, in the last year the maxima have become nicely double peaked and it has been suggested that this is due to the interaction of the two main periods of pulsation of this star. However, how does this square with the analysis of John Greaves that after 1995 there is little evidence for two pulsation periods in the data (see my earlier posts on this topic)?

I wondered if the timescales for the evolution of the double peak fit in with the two periods of 194.0 and 204.8 days that John measured before 1995. If you imagine that the two pulsation periods start out in phase, then after one period of each the peak of the 194.0 day pulsation will be ahead of the 204.8 day pulsation by 204.8 – 194.0 = 10.8 days. After n such periods, the shorter pulsation would be ahead by n x 10.8 days. Looking at the light curve for the star you can see that for the last double peak (September 2022 to November 2022) the two humps were separated by about 3 months or roughly 60 days. This would seem to imply that the two periods would have been in phase n = 60/10.8 ~ 6 periods earlier and this certainly seems feasible looking at the light curve.

So how often would we expect double peaks to be occurring if the two periods of 194.0 and 204.8 days persist? The simple linear addition of two sine curves of the same amplitude but different periods of A and B would result in another sine curve of period 2AB/(A+B) which in this case would be 199.3 days but the amplitude of this would be modulated by a cosine curve of 2AB/(A-B) which is 7,358 days or about 20 years. However, a cosine curve passes through zero twice every period, so the “beat” frequency is half this, i.e. every 10 years. This is only a very rough guide because I am sure that the behaviour is not linear but it seems reasonable given what I said in my earlier posts about how often double peaks occur. Interestingly, the amplitude of the light curve variations does decrease as a double hump approaches.

What is says to me is that we really need more accurate measurements of the light curve to better see what is going on. Have the two pulsation periods begun to die out as John says or are they being hidden in the noise of the data? Perhaps we need regular digital detector monitoring over the next 20 or 30 years to decide this. Anyone fancy this?"



All text and images © Duncan Hale-Sutton 2025 (except the images kindly provided by the BAA).

Confirmation that Z UMa is near maximum brightness

In my last post a few days ago I said I would be having another go at estimating the brightness of the pulsating variable Z Ursae Majoris to confirm my rather rushed observation. Well, last night (9th May 2025) it was clear and, in spite of the moon being bright and 3 days before full, I got my observation (using 10x50 bins):-

Z Uma, 21:45 UT, chart 217.02, A(1)V(4)B, mag. 6.5

Unfortunately the two comparison stars on the chart A and B are a magnitude apart but it was clear that Z was nearer to A in brightness rather than B and this was how I arrived at my estimate.

All text and images © Duncan Hale-Sutton 2025



 

Friday, May 9, 2025

Z Ursae Majoris near maximum brightness

The other night, on the 6th May 2025, I was keen to get a view of Z UMa even though the moon was quite bright (it was two days after first quarter). This star has been rapidly rising in luminosity over the last month and I wanted to get another estimate of its apparent magnitude. Unfortunately, I had to go with my first sight of it as it rapidly clouded up and subsequently I could only see it through gaps in the cloud. Here is my estimate (using 10x50 bins):-

Z Uma, 21:43 UT, chart 217.02, =A, mag. 6.3

This star is recorded as ranging in magnitude from 6.2 to 9.4, so currently it is at maximum brightness.

I will have to have another look in a few days but the moon will be approaching full by then.

All text and images © Duncan Hale-Sutton 2025

Tuesday, April 29, 2025

Pulsating variable V Canum Venaticorum

Last night (28th April 2025) I was able to observe a new variable star - V Canum Venaticorum. This star sits in the constellation of the hunting dogs that chase the great bear (Ursa Major) across the sky. The constellation is very well placed at the moment and is virtually overhead as proper darkness falls. The weather was clear and the moon was just one day past new and not an issue. The end of astronomical twilight is now approaching 11pm BST.

The star is found on BAA chart 214.02. According to the BAA this is an SRa type pulsating variable with a period of about 192 days. It ranges in magnitude between 6.52 and 8.56. The star is found close to the end star of the plough asterism (the star name Alkaid) and lies on the other side of the galaxy M51 (The Whirlpool). I was quite pleased that I could actually see this galaxy in my 10x50 binoculars.

Here is my estimate for this variable star:-

V CVn, 21:53 UT, chart 214.02, E(2)V(3)G, mag. 6.7

Just a reminder about how these estimates are worked. Comparison star E is magnitude 6.5 and star G is 7.0. V was between these two stars in brightness but nearer to E. My estimate put V at 2 points from B and three from G, that is E(2)V(3)G or magnitude 6.7.

All text and images © Duncan Hale-Sutton 2025