T Coronae Borealis on the morning of the 26th December 2023

T CrB is a recurrent nova that is currently of interest because it is likely to go nova sometime soon. The last two eruptions were in 1866 and 1946 (a separation of 80 years) and the current prediction for the next one is 2024.4+/-0.3. It could reach magnitude 2 which would mean it would be roughly as bright as alpha CrB.

The BAA have 3 useful charts to use when locating T. These are a wide 50 degree field, a 9 degree field for use with binoculars and an inverted 2 degree field to be used with a telescope. The chart number is 025.04. T is located near Epsilon CrB. This star (labelled A on the 9 degree chart) forms a roughly equilateral triangle with the stars labelled E and F. T is to the west side of the line between A and F and a roughly halfway between them. There is a small group of three stars to the east of this line which point towards it.

At the moment (5th January 2024) T is about 10th magnitude. Members of the BAA variable star section have obviously been asked to keep an eye on this star but currently the constellation of Corona Borealis is only visible in the morning before sunrise.

On Boxing Day morning just passed (the 26th December) I happened to be awake around 6am and so I thought I would check to see if the nova had appeared. The sky was clear but the moon (1 day before full) was still in the sky in the west and astronomical twilight began at 06:00 UT. Nothing was obvious to the naked eye around that time. With 7x50 binoculars I searched for the location of T without seeing anything. The faintest star I could see in the area (at 06:32 UT) was the star labelled P which was magnitude 8.4. So T was fainter than this at this time. The last confirmed visual observation of this star was around the 1st December but there have been some CCD determinations. So I must try and get up early one morning soon and have a go with the telescope.

All text and images © Duncan Hale-Sutton 2024

Bright Aurora and STEVE on the 5th November 2023

On Guy Fawkes night at the beginning of this month we had an excellent display of the northern lights here in Norfolk and this is only the second time I have seen this phenomena in my lifetime (the other time was in Edinburgh in the early 2000's). The lights were triggered by a strong G3 geomagnetic storm caused by two Coronal Mass Ejections (CMEs) from the sun which arrived on the 4th and 5th November. As you will see from my report below I ended up being more interested in an associated phenomenon called a STEVE which was more noticeable than the aurora itself (follow the link to see more about what a STEVE is).

Here is my report that I sent to the BAA Aurora Section:-

"Having received an alert from the AuroraWatch app on my phone that the Geomagnetic activity at Sumburgh Head had reached over 600 nT at about 1700 UT I went outside to look at the sky about 18:35 UT. The sky was dark by then (Astronomical twilight ended about 18:20 UT and the Moon, at last quarter, hadn't risen). The first thing I saw was a band of milky white light quite high in the sky to the north. Being unclear whether I was seeing some sort of cloud or an aurora, I went to grab my Nikon D90 DSLR and the first picture I took was at 18:42:12 UT (see below). This showed the band of white light curving down towards the eastern horizon and passing though the constellation of Perseus. To the right of it in the picture is a patch of glowing red light.

This I took to be confirmation that this was an aurora and not a cloud formation and I have subsequently learned that the white light is called a STEVE, which is an associated phenomenon. Having only seen an aurora once before in my life, I found myself concentrating on aspects of the STEVE and perhaps neglecting the more commonly observed green dome of light due north.

 

What I thought was important about the arc of white light or STEVE was that it was a complete arch running from the eastern horizon right across the sky to the western horizon. My second picture (18:43:54 UT - see above) shows the arc passing above Polaris near the centre (but slightly to the right) of the frame. I have identified 76 Draconis as a star (at RA 20h 42m 35.0s Dec +82d 31m 52s) near Polaris which sits roughly in the middle of the arc and using software (using the date, time and my location) I have determined that this star was at an altitude of 59 deg. 44 min. So the arc most likely reached about 60 degrees in altitude due north. In my picture, the arc appears to slope further up to the right. I have confirmed that this is because in my haste my camera was not set level. I found that another star located in the arc to the right of polaris (48 Cas RA 2h 1m 57.3s Dec +70d 54m 26s) was at an altitude of 57 deg 6m.

Going back to the picture I took at 18:42:12 UT, by projecting the direction of the line of the arc towards the eastern horizon on a star map it seems that it would pass close to 47 Tauri (RA 4h 13m 56.4s Dec +9d 15m 50.0s) and at this time and location this star was at an altitude of 3 deg. 24 min. and at an azimuth of 78 deg. 46 min. measured eastwards from the north point. So it is likely that the STEVE intercepted the horizon at an azimuth of about 79 degrees (but it could be a little less than this if the arc was still curving inwards towards the north).

By 18:50:57 the white arc of the STEVE had dissipated leaving only a red glow in the eastern horizon as seen in the picture taken at this time (see above). However, after this time its strength grew again as can be seen in the images taken at 18:54:47 and at 18:56:19 (see below) and the arc was again a complete arch across the sky.

During some of the time when I the STEVE was at full strength I noticed that it appeared to be flowing from east to west along the white arc. This was evident by the fact that there were bands moving quite quickly along the arc (lines of brighter intensity with a direction perpendicular to the line of movement) and I was surprised by how fast they were moving.  I would say that they covered about 15 degrees of arc in a few seconds (so may be 7 or 8 degrees per second). 

My attention then turned to the western horizon and the picture taken at 19:00:43 shows this (see above - note that here I had increased my exposure time from 15s to 30s; see my note below about my camera settings). Although there is some evidence for cloud to the left of this picture, the white arc of the STEVE and the red glow (now to the left of it) is very much in evidence. You can also see the green glow of the aurora to the right towards the north above some television aerials. What is ineteresting to me is the symmetry of the STEVE display. What is seen in the west is a reflection of what is seen in the east and they were happening at the same time. 

By about 19:02 UT the STEVE began to dissipate again and so the part of the display I had seen lasted about 20 minutes. At 19:03:56 I took a picture towards the north (above - actually slightly east of north) at a lower elevation which shows the green and slightly red light of the aurora in that direction. At 19:08:14 the red glow in the east associated with the STEVE could still be seen. I went in for my dinner around this time but I came out again about 20:00 UT to take some more photos. Some greenish tinge low in the sky could still be seen to the north at 19:58:15 UT.

A note about camera settings. All pictures attached to this report were taken on a Nikon D90 with a Nikkor VR 18-105 f/3.5-5.6 ED lens. The settings were a focal length of 18mm, ISO3200 at f/3.5 giving a field size of 66x46 degrees approximately. Up until and including the picture taken at 18-56-19 UT the exposure time was 15s. After that it was 30s."

All text and images © Duncan Hale-Sutton 2023

Seven stars in one night (22nd October 2023)

A week last Sunday (the 22nd October) we had some clear weather late in the evening that allowed me to carry out a substantial bit of variable star observing. I think I am getting better at locating the stars in question and then estimating their brightness. One of the tricks of finding the targets is to be able to recognise star patterns and I have made things easier for myself by making some scribbled notes on my location charts. It is helpful to draw in lines between stars that make a shape or pattern. It becomes easier to recognise a shape when you return to it another time. Also, understanding how a chart relates to the wider constellation in which it is found is very helpful when pointing your binoculars in the right direction.

On that Sunday evening there was a bit of light cloud earlier on that was drifting over the sky. The moon was at first quarter and it was due to set at 22:40 UT. Astronomical twilight ended at approximately 18:40 UT.

I began with two variables in Draco on BAA chart 106.04. As usual I was using my 7x50 binoculars. At 22:12 UT TX Draconis (near the star Eta) was brighter than star N (=7.7 mag.). At 22:16 I determined that it was fainter than star K(=7.0) but not by much. My estimate was K(2)V(5)N which made it magnitude 7.2. This is in very good agreement with other observers from the BAA.

On the same chart we have AH Draconis. At 22:27 UT I saw that AH was fainter than star 1 (=7.0 mag.) but not by much. At 22:33 I thought it was equal in brightness to star 2 (=7.3), so my estimate was magnitude 7.3. Again this is in very good agreement with other observers.

Cygnus was still at a reasonable altitude at this time so I switched to observing CH Cygni on chart 089.04. By then most of the light cloud had dissipated. At 22:53 UT I could see that CH was much fainter than star A (=6.5 mag.) on that chart. At 22:56 I felt CH was fainter than star D (=8.0) but not by much. At 22:59 I thought it was brighter than star F (=8.5) and my estimate was D(1)V(4)F, that is magnitude 8.1. CH is an unusual variable star as I have described previously. At the moment it has faded quite a bit since it peaked in brightness between August last year and January this year (it reached about magnitude 6.5). Since June its luminosity does appear to be on the rise again.

I moved on to my next star which was pretty much overhead. This was RW Cephei on chart 312.02. At 23:16 UT RW was fainter than stars P (=6.2) and B (=6.5). At 23:18 I saw that it was brighter than star E (=7.3) but closer to B. My estimate was B(1)V(3)E or magnitude 6.7.

My fifth star to observe that night was GO Pegasi (chart 103.02). At 23:37 UT I found that GO was fainter than star B (=7.0) and brighter than E (=7.8) and my estimate was that it was mid-way between the two, i.e. B(1)V(1)E or magnitude 7.4.

My final two stars were in the constellation of the Great Bear. By midnight (1am BST!) this constellation is rising again in the north east. At 23:55 UT I saw that Z UMa is similar in brightness to star B (=7.3) on chart 217.02. At 23:57 I determined it was brighter than star D (=7.9) and at 23:59 roughly equal to star C (=7.5). So my estimate was magnitude 7.5.

Finally, on the same chart and just creeping into the 23rd October at 00:04 UT I noted that RY UMa was brighter than stars 4 (=7.7) and 5 (=8.3). At 00:06 I estimated that RY was between stars 2 (=7.4) and 1 (=6.7) but closer to 1. My estimate was 1(2)V(5)2 or magnitude 6.9.

All these estimates are in good agreement with other observers from the BAA.

All text and images © Duncan Hale-Sutton 2023

Recent observations of some variable stars

Over the last week we have had a couple of occasions when the sky has been clear enough for a while for me to get out and observe some variable stars. Last Saturday (7th October) I had just long enough to observe GO Pegasi before the murk closed in. That night the moon was 1 day past last quarter and not due to rise until 22:39 UT. Darkness is now falling earlier in the evening and astronomical twilight ended at 19:20 UT on that day. At 21:55 UT there was some hazy cloud around and some parts of the sky were obscured, however, the constellation of Pegasus was pretty clear and I was able to determine that GO was fainter than star B (=7.0 mag.) on BAA chart 103.02 but brighter than star E (=7.8 mag.). It was closer in brightness to star E and my estimate was B(3)V(5)E which made it magnitude 7.3.

This star doesn't have much of a range in magnitude variation (just 0.77 according to the BAAVSS) and, probably because of this, it doesn't appear on the list of beginner's variable stars as described by them. But then there are no beginner binocular variable stars listed in Pegasus, which seems a shame, and this is why I think I picked this one out of the BAAVSS observation program for pulsating stars. I say a shame because Pegasus is well placed at this time of year and is a prominent constellation in the sky. After a recent run of being around magnitude 7.6 it has brightened recently to 7.2 or 7.3 (near the maximum of its range of brightness) and I am glad to say that I am not the only BAA observer to have recorded this! The last time it reached this magnitude was back at the beginning of the year over 280 days ago. This seems a bit odd for a star that supposedly has a period of 79 days! However, I have found a paper by Kate Blackham (pdf) where she can't find any periodicity in this star and has declared it to be an irregular.

Two days ago on the 9th October we had another evening when there was a brief period of clear weather. Again there was quite a bit of hazy cloud and one or two more thicker patches of accumulation. The variable star TX Draconis is now heading down towards the west in the evenings but it is still at a good altitude. At 21:12 UT TX was fainter than star K (=7.0 mag.) on BAA chart 106.04 but brighter than N (=7.7 mag.). My estimate was K(5)V(2)N which made it magnitude 7.5. Another observer at the BAA on the same night estimated it to be visual magnitude 7.3, so we are in reasonable agreement. I had been intending to look at AH Draconis as well but by then a bit of cloud was obscuring my view.

I went on to look at RW Cephei which I have described before. At 21:36 RW was fainter than star P (=6.2 mag.) on chart 312.02 but brighter than star E (=7.3 mag.). My estimate put it midway in brightness between the two, namely B(1)V(1)E making it magnitude 6.9. This star hasn't changed much in brightness by my reckoning since I last looked at it on September 12th. Then I estimated to be 6.8. I think these results are in pretty good agreement with other observations from the BAA and AAVSO.

All text and images © Duncan Hale-Sutton 2023

The brightening of the yellow hypergiant RW Cephei (4th September 2023)

Last week (4th September) I was able to get out and observe the variable star RW Cephei. The conditions weren't that great as the waning gibbous moon (2 days from last quarter) was rising at 20:20 UT and the sky was hazy. Astronomical twilight ended at about 20:40 UT.

Using my 7x50 binoculars I was able to find RW using chart 312.02 from the BAA. At 20:43 UT RW was fainter than both nearby stars P (mag. 6.2) and B (mag. 6.5) on that chart. However, at 20:46 UT I determined it was brighter than star E (mag. 7.3). My estimate was that it was one "point" from B in brightness and two "points" from E, namely B(1)V(2)E which made it magnitude 6.8 (to 1 d.p.). This is in good agreement with other data from the BAA.

As noted before (in December 2022 and January 2023) this star has recently gone through a period of dimming similar to that which occurred to Betelgeuse in 2020. That dimming now seems to be over as its brightness has returned to its normal range of magnitudes as seen by the plot generated from the BAAVSS below:-

My latest data point is the black circle at the extreme right of this light curve (magnitude on the vertical axis, calendar date on the horizontal). In a recent paper in The Astronomical Journal the authors have presented some images of this star obtained through interferometry which show that during the period of dimming the star's surface brightness appeared asymmetric. They suggest that this has been caused by a mass ejection of material that has resulted in a dust cloud that is blocking the light from the stellar photosphere. This is similar to what happened to Betelgeuse.

All text and images © Duncan Hale-Sutton 2023 (except for the image from the BAAVSS)

Variable stars TX and AH Draconis, AC Herculis and CH Cygni (19th August 2023)

I have had quite long spell of not being able to do much variable star observing (the last time was at the back end of May). The cause was the poor weather and the light evenings. This month (August) I had an opportunity to get something done on the 19th. The moon was 3 days past new and astronomical twilight ended at 21:40 UT. We had a nice clear sky but I had forgotten how hard it is sometimes to identify where a particular variable is in relation to other stars. It can take as long to refamiliarize myself with a star field as it takes to make the actual magnitude estimate.

I started with TX Draconis which I now know quite well and wasn't too difficult to find. The end two stars of Ursa Minor (Kochab and Pherkad) point to Eta Draconis and the pentangle of stars containing TX are nearby. At 22:03 UT, TX was definitely fainter than star K (at magnitude 7.0, see chart 106.04). At 22:08 UT I couldn't distinguish it in brightness from star N (magnitude 7.7). So that was my estimate. This was in good agreement with other observations by BAA members at this time.

Moving across to AH Draconis which is in the same 9 degree field, at 22:11 UT AH was fainter than star 1 (mag. 7.0) but brighter than star 6 (mag. 7.8). At 22:16 my estimate was that AH was midway between 2 and 6 in brightness, i.e. 2(1)V(1)6 or magnitude 7.6. This may be a little fainter (by 0.2 magnitudes) than other BAA estimates.

I now switched to looking at AC Herculis. This star is not so easy to find. It is located quite a way from the main asterism which forms the body of this greek hero - in fact it is better to draw a line between Delta and Beta Lyrae and continue this south and this will get you close to where AC is found. The nearest bright star is Flamsteed 109 and from there you can hop to the variable. At 22:46 I saw that AC was definitely brighter than star E (mag. 8.2 on chart 048.04) which is right next to it. At 22:48 UT I determined AC was midway in brightness between stars C (=6.9) and star D (=7.4), that is C(1)V(1)D or magnitude 7.2. This was in good agreement with other observations by BAA members.

Finally, I moved on to CH Cygni. This star has the advantage that it can be found near the outstretched wing tip of the swan asterism close to Iota and Kappa Cygni. At 23:10 CH was definitely fainter than star A (magnitude 6.5 on chart 089.04) which is very close by. It was also fainter than star W (=7.3) which is a bit further away. At 23:19 I estimated CH was similar in brightness to star D (=8.0).  Again, this was in good agreement with other observations by BAA members.

All text and images © Duncan Hale-Sutton 2023

How many stars can you see in the Great Square of Pegasus?

The time for the Perseid meteor shower has been and gone (the peak was on the 12/13th August) and I missed out as it was cloudy that night here in Norfolk. The following night at 1.15am BST on the morning of the 14th August I did have a peep outside and was presented with a really clear dark sky that you just don't see that often. Jupiter is now up at this time and it won't be long before it is in our evening sky again. What interested me was just how good the sky transparency was. One of the ways of testing this is to try and see how many stars you can make out with the naked eye within the Great Square of Pegasus which was well placed at this time. This is a good test of your eyesight and a good test of how dark your sky really is. I could see quite a few stars so I decided to spend some time totting them up.

Bob King has described his attempts at doing this in his very good Sky and Telescope article. In the end I counted 9 or 10 and using his list of stars within this asterism I reckon that I was seeing down to magnitude 5.8 which is pretty good.

I used to think we had good dark skies where we are in Norfolk but over recent years I have had to admit that light pollution is getting worse where we are. We have Norwich just about 10 miles away and the lights from this city are getting worse as it expands further out towards the NDR. To the east is Great Yarmouth but that only shows up faintly. Nearby we have some intrusive lights from a local radar station to the north.

When I realistically place our night sky on the Bortle Scale I can see that we are actually approaching a suburban sky (class 5). On better nights we might just be classed as a 4 (rural/suburban transition) but I think that is pushing it as evidenced by the fact that I couldn't see stars fainter than 6th magnitude. I certainly have never seen the Zodiacal Light here and I did try to see M33 with the naked eye but didn't spot it. However, this may be something to try on another dark night. 

All text and images © Duncan Hale-Sutton 2023