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

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

More variable star observations

This week we have had some evenings of clear weather and I have been able to get out with my 10x50 bins and make a few more observations of variable stars. On Tuesday night (22nd April 2025) it looked clear but unfortunately cloud moved in soon after I started. The moon is currently out of the way having now passed last quarter and it now gets properly dark about 22:30 BST. I managed to make one observation of Z Ursae Majoris:-

Z Uma, 21:47 UT, chart 217.02, =C, mag. 7.5

This star has rapidly brightened since its fade at the end of last month. On Thursday evening (24th April 2025) it was clear again and this time the transparency was much better. I made another observation of Z UMa to check what I had seen on Tuesday):-

Z Uma, 21:45 UT, chart 217.02, B(1)V(1)C, mag. 7.4

Another person from the BAA also measured Z to be the same magnitude on this night. I went on to look at three other pulsating stars before the cloud came in:-

RY Uma, 21:54 UT, chart 217.02, 1(2)V(5)2, mag. 6.9

TX Dra, 22:07 UT, chart 106.04, K(2)V(5)N, mag. 7.2

AH Dra, 22:11 UT, chart 106.04, 1(1)V(2)2, mag. 7.1

 

All text and images © Duncan Hale-Sutton 2025

 

 

Faint aurora seen on the 16th April 2025

A week ago I had a major auroral alert on my phone from AuroraWatch. This started about 2pm BST and continued on till 10pm. During this time the geomagnetic activity ranged from 500 to 750 nT according to the magnetometer at Sumburgh Head. I began taking pictures about 21:30 but for the most part I was thwarted in seeing very much due to thin cloud and haze. However, on examining my photographs I did pick out some activity at 22:17 (21:17 UT) as can be seen below:-

 

This is not easy to see but there is a distinct pink patch to the right of the cottage near the horizon. In this area the constellation of Cygnus is rising and the pink aurora is near the back of the asterism that makes up the body of the swan and its right wing. In fact, I think there is generally a pink glow that extends from here at about the same altitude towards the constellation of Cassiopeia at the left of the picture. This picture was taken on a Nikon D90 with a Nikkor VR 18-105 f/3.5-5.6 ED lens at 18mm. The exposure was 20s at f/3.5 ISO 1600.

Looking harder at some of my other photographs there was another taken 8 minutes earlier at 22:09 (21:09 UT) which showed some activity:-

This was a shorter exposure of 8 seconds and I had to increase the brightness to bring out the detail. Again there is a pink colouration above and slightly to the left of the cottage. Both images face roughly north.

Other BAA observers saw this aurora about the same time I did and had a much better view (see, for example, this nice image by Grant Privett in Salisbury). 

All text and images © Duncan Hale-Sutton 2025

Recent variable star observations

Just over two weeks ago on the evening of the 30th March 2025 I made a couple of observations of two pulsating variable stars. The moon was one day after new and astronomical twilight ended at about 20:20 UT. The sky transparency was average and nothing to write home about.

Using 10x50 binoculars the first star I looked at was Z Ursae Majoris. This was obviously going through one of its minima in brightness as it was pretty faint:-

Z Uma, 21:13 UT, chart 217.02, =H, mag.8.7

I think, to be honest, I was struggling to estimate the brightness accurately because the star was getting near the limit of my binoculars and so my estimate is 0.6 magnitudes brighter than two other BAA visual observers on this night (their estimates were 9.2 and 9.4 averaging to 9.3; also there was one DSLR estimate of 9.1). However, when I look at the AAVSO data, they have two visual estimates on this night of 8.4 and 8.8 averaging to 8.6 in rough agreement with what I saw so I don't feel too bad.

Using the same chart I looked at RY Ursae Majoris:-

RY Uma, 21:25 UT, chart 217.02, =2, mag. 7.4

This observation seems more in keeping with other BAA observers. 

All text and images © Duncan Hale-Sutton 2025

Partial Solar Eclipse on the 29th March 2025

The good weather over the last few weeks extended to Saturday before last when we had a partial solar eclipse viewable in the UK. From Norwich, the eclipse was to begin at 10:10 UT and maximum coverage would be seen at 11:06 when the magnitude of the eclipse was predicted to be 0.413. The magnitude is a measure of the depth of the eclipse and is the fraction of the Sun's diameter that is occulted by the Moon. The eclipse was then predicted to end at 12.03 UT.

I was able to set up my Celestron NexStar 102 SLT on my HEQ-5 mount well in advance of the start of the eclipse. I intended to project the image from the telescope onto white paper using a 25mm eyepiece and a star diagonal. I used my Samsung Galaxy A21s phone camera to take images and the first image I took was at 10:16:52 UT:-

You can just start to see that the moon is creeping over the western side of the sun. Fortuitously the solar image is just about the right way up with north uppermost and west to the right (this resulted from using the combination of the star diagonal and the projecting the image onto paper). The prominent sunspot group on the left-hand side is AR4046 and to get an idea of what the sunspot activity looked like on this day here is the SDO image (taken at 19:54 UT, courtesy of NASA/SDO):-

 

After deleting poor images and duplicates, I had a total of 18 images from that morning but only until just after maximum eclipse. Rather than show all of these I have picked out six that are approximately 10 minutes apart and show the progression of the moon across the sun. The next image was taken at 10:25:36 UT:-

The chunk taken out of the Sun has increased noticeably but still appears to be increasing from the west. The next image was taken at 10:35:16:-

The same applies here. The moon is slowly encroaching over the sun. The fourth image was taken at 10:47:41:-

Now it appears that not only has the area of the sun that is occulted increased but also the moon appears to be moving northwards. The 5th image was taken at 10:54:42:-

The obscuration is approaching maximum and it is more noticeable that the moon has drifted northwards. The 6th and final image was taken at 11:06:25 and this is within 19 seconds of the eclipse maximum:-

From this image we can measure the percentage area of obscuration. Looking back at my previous discussion of this, I have measured the chord AB to be 994 pixels and the diameter to be 1200 pixels. This gives that the angle w is 1.952 radians (or about 112 degrees) and the observed obscuration is 33% (assuming that the sun and the moon have the same apparent diameter). From the predicted magnitude of 0.413 we can find the predicted obscuration and this is 30%. So pretty much in agreement given the potential errors. 

All text and images © Duncan Hale-Sutton 2025 (except the SDO image).

Final evening observations of Venus

The 2024-2025 eastern elongation of Venus is now over as the planet reached inferior conjunction on the 23rd March and is now appearing in the morning sky. Before this happened I was able to make a few more observations of the planet as its phase shrank to a thin crescent. Firstly, I saw the planet on the 5th March 2025 in clear skies but relatively poor seeing. Venus was at an altitude of about 24 degrees in the West just after sunset. Here is the page from my notebook:-

I made the drawing using my 140mm Orion Maksutov-Cassegrain between 17:35 and 17:52 UT. The phase has shrunk considerably since my last drawing on the 25th January. From the drawing I estimated that the phase was 13% by measurement. This was slightly larger than the predicted phase of 11.2% predicted by the BAA. Notice also how the size of the planet has grown considerably from 29.6 arc seconds on the 25/1/25 to 51.5 arc seconds in this observation. 

On the 13th March at 18:16 UT I captured an image of Venus using my Tasco 18-36x spotting scope:-

 

This terrestial telescope has an aperture of about 50mm. This picture was taken at 36x and I used my Samsung phone to capture it. At this time the phase of Venus was about 5% and the planet was at an elongation of 19 degrees.

The final drawing I made of Venus was on the 17th March and by then the phase appeared to have shrunk to just 1%:-

Here I used my NexStar 102 SLT set up at the front of the house which is west facing. Venus was by this date not very far above the horizon after sunset (a mere 5 degrees in the west). The low altitude caused the seeing to be very poor but it made for a very beautiful sight. The crescent of the lit side was so thin that the atmosphere caused the image to flicker in different colours, like diamonds on a necklace. What's more, after careful observation, it was possible to see that the cusps of the crescent had extended further round the planet than would be expected for solid body with no atmosphere and I have tried to show this in my drawing. The cusps on such a body would be expected to end diametrically opposite each other where the terminator meets the edge of the planet. Instead the light carries on past this point causing appearance of the cusps to curve back on each other. I was very pleased to see that Paul Abel at the BAA produced a very similar drawing a day later.

By comparing what I could see at 73x with 5 phase diagrams ranging in phase from 1 to 5% in steps of 1% I estimated the phase to be 1% and this is smaller than the 3% predicted by the BAA. 

Finally, on the 18th March at 18:12 I captured my last image of Venus using my spotting scope at 36x again:-

 

 All text and images © Duncan Hale-Sutton 2025