Six variable star estimates (11th September 2024)

About two weeks ago, on the night of the 11th September, we had some very good clear skies and the first quarter moon had set by 21:23 UT. We are moving into autumn now and it gets properly dark by 20:30 UT. The transparency of the sky was shown later on in the night when looking at the variable Z UMa but I will come to that shortly.

I began with a couple of stars in Draco. Using my 10x50 binoculars and BAA chart 106.04, at 21:50 UT I could see that TX Dra was fainter than star K (magnitude 7.0) but marginally brighter than star N (mag. 7.7). My estimate was K(5)V(2)N or magnitude 7.5.

On the same chart is AH Dra. At 22:00 UT I could see that AH was fainter that star 1 (mag. 7.0) but brighter than star 2 (mag. 7.8). At 22:09 UT my estimate was that is was roughly equal in brightness to star 2, that is magnitude 7.3.

The constellation of Cygnus is still high in the sky at this time and so I next looked at the star CH Cygni on chart 089.04. At 22:24 UT CH was fainter than star A (mag. 6.5) but brighter than star W (mag. 7.3). At 22:30 UT my estimate was A(3)V(5)W or magnitude 6.8.

The constellation of Cepheus, by contrast, was directly overhead. Using chart 312.02 at 22:47 UT I saw that the variable RW Cep was fainter than star B (mag. 6.5) but brighter than star E (mag. 7.3). At 22:50 UT my estimate was that it was midway between these two stars in brightness, that is B(1)V(1)E, i.e. magnitude 6.9.

Now onto a couple of stars in Ursa Major. This constellation hangs quite low in the sky in September at midnight BST. It almost "stands" on the northern horizon. I had been thinking because of its low altitude that it might be difficult to view the variable stars I had in mind due to absorption in the atmosphere but it was a testament to the clarity of the sky that this wasn't the case.

Firstly, I had a look at Z UMa on chart 217.02. This star was very faint but just visible. At 23:05 UT Z was fainter than stars H (mag. 8.7) and L (mag. 8.9)!! Now I couldn't see star M (mag. 9.5) but I reckoned that Z was only a couple of tenths fainter than L. So my estimate was L-2, i.e. magnitude 9.1. This must be one of the faintest observations of this star I have ever recorded.

On the same chart is the variable RY UMa. At 23:18 UT RY was fainter than star 1 (mag. 6.7) but brighter than star 2 (mag. 7.4). At 23:23 UT I thought that RY was closer in brightness to 2 rather than 1 so my estimate was 1(5)V(2)2, i.e. magnitude 7.2.

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

All text and images © Duncan Hale-Sutton 2024

Noctilucent cloud activity in June 2024

Earlier in June I saw a couple of displays of noctilucent clouds (look at this previous post to find out what these clouds are and how they are formed). The first was on the night of 23rd/24th June when we were in Suffolk near Bawdsey and I initially saw them at 21:51 UT:-

I estimated that they reached a maximum elevation of about 18 degrees above the horizon and stretched from about azimuth 300 to azimuth 10 (azimuth 0 points due north and then increases eastwards along the horizon - so due east is 90 degrees, south 180 and west is 270). They were mostly in the form of bands (type 2) and waves (type 3).

I carried on seeing them for about 25 minutes (until 22:15 UT):-

By then the clouds had sunk lower to the horizon (just a maximum elevation of 12 degrees) and they stretched from azimuth 313 to 357 degrees. Both pictures were taken on a Samsung SM-A217F camera phone with an exposure of 1/10s, f/2.0, ISO 2000.

Five days later on the night of the 28th/29th June I observed another display from my home in Neatishead. Again, I caught sight of them at a starting time very similar to before (21:52 UT):-

You can see the NLC's as white wavy bands (type 3) behind the chimney pot of the house next door. Some foreground normal cloud is obscuring the view. I reckoned that the maximum elevation of the clouds stayed pretty much constant at 18 degrees above the horizon.

Eight minutes later at 22:00 UT the clouds appear brighter as the sky darkened:-

There appeared to be some brighter knots in the wavy clouds. At 22:12 UT the clouds appeared very bright and the structure was more complex:-

Also the clouds didn't appear to extend so far eastwards (although part of this may be due to obscuring foreground cloud). At 22:28 UT the clouds began to fade and I stopped observing:-

The camera and exposure settings were the same as above.

All text and images © Duncan Hale-Sutton 2024

The great solar storm of 2024 (10th May)

On the night of the 10th/11th May we had a severe G5 geomagnetic storm which caused auroras to be seen over a wide range of earth latitudes. On the night in question I had red alerts from my AuroraWatch UK app on my phone starting about 7pm BST. Initially, the strength of the alerts were from about 300 to 500 nT at Sumburgh Head but then at 10pm BST it hit about 950 nT and I knew we were possibly going to be in for a good display (compare this with the alerts we had for the aurora on the 5th November 2023). The weather was clear at this time but there was no point in looking for the aurora until near the end of twilight (the sun set about 20:40 BST and it wasn't going to get fully dark until 23:30 BST). There was a 2 day old moon but it didn't interfere with the observations as it was very low in the north west.

I went outside to have a look at the sky about 10.30pm and I could see a band of pale light over the northern horizon, so I went in to collect my camera and tripod. The first picture I took was at 22:42 BST and this clearly showed a green arc of aurora stretching across the sky, the upper parts of which crossed the constellation of Cassiopeia. From photographs I estimated that the lower part of the arc was at a maximum height of 11 degrees above the horizon whilst the upper part was at a maximum height of 28 degrees. It stretched roughly 60 degrees either side of true north.

Here is the second picture I took at 22:42:53 BST:-

You can clearly see vertical green rays in this arc and the W of Cassiopeia near the centre of the image. In all the images I took that night I used a Nikon D90 with a Nikkor VR 18-105mm f/3.5-5.6 ED lens at 18mm. All exposures were 5s at ISO 1600 at f/3.5.

I continued to take a series of images of this arc. By 22:55 BST the location and size of the arc had already changed significantly. The maximum height of the bottom and top of the arc above the horizon had changed to 17 and 35 degrees, respectively and it stretched to 70 degrees either side of due north. I also began to see some pink rays due east at about an altitude of 36 degrees. Here is a picture of the arc at 22:58:27 BST looking north west:-

The constellation of Auriga can be seen just above the trees in the centre, whilst to the left Castor and Pollux in Gemini are above the big oak tree. 

At this point in time I took a series six images about 10s apart. The rays in the arc were changing rapidly from image to image. Here is one of those images taken at 23:03:51 BST:-

You can now see that the bottom of the arc has nearly cleared the W of Cassiopeia and that the rays in the arc are well defined.

By 23:06 the top of the auroral arc had reached the zenith at its maximum and the lower part was 27 degrees above the horizon. So not only was the arc appearing to move southwards it was also swelling in extent. A few minutes later the display began to change and, unfortunately, the weather also deteriorated as well, as thin cloud began to drift in from the coast. This was perhaps the most dramatic part of the display as the auroral arc gave way to more spectacular fans of pink and red rays. This was one photographed at 23:11:25 BST:-

This view looks almost due east. To the upper right can be seen the distinctive shape of Corona Borealis. The bright star to the lower left is Vega. The colours here are very impressive ranging from red towards the lower middle of the picture to purple/pink in the upper right.

Similar patterns of pink and rays were seen in the west with the green coloration more to the north. This was the scene in this direction at 23:16:09 BST:-

Stars are just about visible but it is getting difficult to recognise constellation patterns, however, you can see the front of the "big dipper" pointing downwards at the top of this picture. Nearly four minutes later there was a nice mixture of red and green rays seen to the north:-

This was taken at 23:19:55. The front of the big dipper is again pointing downwards into the picture from the top but more to the left. The bright star halfway up the image and slightly to the right of centre is polaris. Ursa Minor extends upwards from this star. 

The aurora around this time was coming and going as gaps appeared in the ever increasing cloud. Finally, we were treated to an unusual phenomenon when rays of the aurora appear from the zenith and this is called a corona:-

It is much easier to make out the shape of the big dipper to the top right of this image (taken at 23:22:41 BST). Arcturus in Bootes is the orangey bright star to the far left. Zenith at this time is roughly where the star Mizar is located (one star from the end of the handel of the big dipper). The colour of the rays above my head at this point were strongly pink/purple. Also at this time the display was so bright that it was lighting up the garden around me.

I carried on taking pictures of bits of the display until 23:48 BST but soon after this I gave up and went to bed because of the deteriorating weather.

All text and images © Duncan Hale-Sutton 2024

Predicting the relative positions of the binary star Xi Bootis

In my previous post I described an observation of the binary star Xi Bootis that I made on the 1st May. From a photograph I was able to make a measurement of the separation and position angle (PA) of the pair and found this to be about 5.5 +/- 0.4 arcseconds and 291 +/- 3 degrees, respectively. This has lead me to wonder if I could get a prediction for these quantities using measured orbital properties of the binary. In my copy of Norton's 2000.0 star atlas and reference handbook (Longman Scientific and Technical 1989 edited by Ian Ridpath, 18th edition) there is a table of elements of some visual binaries (p146, table 46) and in this list is an entry for Xi Bootis (ADS number 9413 in the New General Catalogue of Double Stars). The orbital parameters are as follows:-

Orbital Period P (years) : 151.505

Date of periastron T : 1909.361

Semi-major axis of orbit a (arc seconds): 4.904

Eccentricity of orbit e : 0.512

Inclination of orbit to plane of sky i (degrees) : 140.04

Argument of periastron ω (degrees) : 203.92

PA of ascending node Ω (degrees) : 348.1

The first thing to note is the date of periastron which is when the two stars are closest. The last periastron was in 1909, the next one will be in 1909.361 + 151.505 = 2060.866 which I reckon is the 11th November 2060.

So how do you predict the relative position of these stars using this data? Well, there is a computer program written in Basic that you could use written on page 145 of Norton's 2000.0 but the alternative is to search the web for someone who has provided an online calculator. Such a person is Roger Wesson who is an astronomer at Cardiff University and his calculator can be found here. Unfortunately, Roger does not list the orbital parameters for Xi Boo in his star name look up but you can type in the orbital parameters given here.

The 1st May 2024 as a fraction of a year is, I think, (31 + 29 + 31 + 30 + 1)/366 = 122/366 = 1/3 (or 0.3 recurring as a decimal), so we can write this date approximately as 2024.333. Using Roger's calculator the predicted separation and PA of Xi Boo on this date was 4.81 arcseconds and 289.8 degrees, respectively. The PA is in good agreement with what I observed but the predicted separation is marginally smaller than what I saw but I wouldn't read a lot into this.

If you look at the bottom of Roger's page there is a nice little animation that you can play which shows how Xi Boo B moves around A. I have used the calculator to predict the separation and PA of this binary for the next 150 years in 10 year intervals starting at 2024.0. The plot is shown below:-

As you can see from the graph, Xi Boo B is moving round from a westerly position to a more southerly one over the next 30 years. Also, the PA and separation are decreasing more rapidly over this period (in 2064.0 the separation is just 2.16 arcseconds). As a result, it is a good time to start observing this pair as the changes will become more noticeable!

The question remains as to how reliable are the parameters for the orbit for Xi Boo? I have found another website by Gianluca Sordiglioni which lists these quantities for this binary and they are a little different to the ones presented here. However, I don't expect the predictions for separation and PA to be radically different. 

Here are the tabulated values for the points in the graph above using the oribtal parameters listed here.

2024.0 : 4.85 : 290.4

2034.0 : 3.90 : 270.5

2044.0 : 3.08 : 238.7

2054.0 : 2.63 : 191.3

2064.0 : 2.16 : 125.5

2074.0 : 2.76 : 53.5

2084.0 : 4.23 : 21.3

2094.0 : 5.47 : 5.2

2104.0 : 6.36 : 354.4

2114.0 : 6.92 : 346.0

2124.0 : 7.19 : 338.5

2134.0 : 7.20 : 331.2

2144.0 : 6.96 : 323.8

2154.0 : 6.50 : 315.5

2164.0 : 5.83 : 305.6

2174.0 : 4.98 : 292.7

All text and images © Duncan Hale-Sutton 2024

Double Stars - Xi Bootis (1st May 2024)

Xi Bootis is my fifth and final double star observation from the night of the 1st May (see my previous post for a discussion of this). Here is my image:-

 

This was a 5s exposure at ISO 1600 on a Nikon D90 at the prime focus of a 140mm Maksutov Cassegrain (an Orion OMC-140). The picture can be better seen by 'clicking' on it. The image is being viewed at full scale (in other words it has not been binned up). Xi Boo A and B are marked and these two stars are visual magnitude 4.70 and 6.97 respectively (actually A is a BY Draconis variable and ranges in brightness from 4.52 to 4.67). The image scale is 0.5859 arcseconds per pixel and this is a 1200x800 pixel crop of the original.

My method for orientating the image has been described in a previous post. Using this I have made some measurements of the separation and position angle (PA) of Xi Bootis (for a discussion of PA and how it is measured please again refer to my previous post). Three measurements of the separation gave me 5.6, 5.8 and 5.0 arcseconds which gives an average of 5.5 +/- 0.4 arcseconds. Again three measurements of PA gave 288.4, 294.0 and 290.6 degrees which averages to 291 +/- 3 degrees. 

This is probably the most interesting of the five double stars I photographed that night because this pairing is a proper binary system with an orbital period of 151.5 years. I have in my possession an old copy of the Webb Society's double star catalogue (The Webb Society Observer's Handbook, Vol. I Double Stars, London 1975) and this star is listed on pages 89 and 109 (STF 1888). The average separation and PA between 1964 and 1974 was 7.1 arcseconds and 342 degrees. So in the 50 odd years since those observations were made the system has changed quite a bit (as you would expect). In 2019 the separation and PA were 5.2 arcseconds and 298 degrees. My measurement of the separation is in good agreement but I think the PA has decreased even further since that date.

All text and images © Duncan Hale-Sutton 2024

 

Double Stars - Nu Draconis (1st May 2024)

Nu Draconis is my fourth double star observation from the night of the 1st May (see my previous post for a discussion of this). Here is my image:-

 

This was a 5s exposure at ISO 1600 on a Nikon D90 at the prime focus of a 140mm Maksutov Cassegrain (an Orion OMC-140). The picture can be better seen by 'clicking' on it. The image is being viewed at full scale (in other words it has not been binned up). Nu 1 and 2 Dra are marked and these two stars are equal in brightness both being visual magnitude 4.88. The image scale is 0.5859 arcseconds per pixel and this is a 1600x1067 pixel crop of the original.

My method for orientating the image has been described in a previous post. Using this I have made some measurements of the separation and position angle (PA) of Nu Draconis (for a discussion of PA and how it is measured please again refer to my previous post). A couple of measurements of the separation gave me 106.65 and 107.71 pixels. This averages to 107.18 pixels and, at 0.5859 arcseconds per pixel, this is 62.8 arcseconds. Again a couple of measurements of PA gave 311.2 and 310.8 degrees which averages to 311.0 degrees. The published separation and PA for this double star is 62.3 arcseconds and 311 degrees, so in very good agreement.

All text and images © Duncan Hale-Sutton 2024

 

Double Stars - Kappa Bootis (1st May 2024)

Kappa Bootis is my third double star observation from the night of the 1st May (see my previous post for a discussion of this). Here is my image:-

 

This was a 5s exposure at ISO 1600 on a Nikon D90 at the prime focus of a 140mm Maksutov Cassegrain (an Orion OMC-140). The picture can be better seen by 'clicking' on it. The image is being viewed at full scale (in other words it has not been binned up). Kappa 1 and 2 Boo are marked and Kappa 1 magnitude is 6.69 whereas Kappa 2 is a Delta Scuti variable ranging in brightness from 4.50 to 4.58. The image scale is 0.5859 arcseconds per pixel and this is a 1200x1200 pixel crop of the original.

My method for orientating the image has been described in my last post. Using this I have made some measurements of the separation and position angle (PA) of Kappa Boo (for a discussion of PA and how it is measured please again refer to my previous post). A couple of measurements of the separation gave me 23.60 and 23.02 pixels. This averages to 23.31 pixels and, at 0.5859 arcseconds per pixel, this is 13.7 arcseconds. Again a couple of measurements of PA gave 233.6 and 235.6 degrees which averages to 234.6 degrees. The published separation and PA for this double star is 13.5 arcseconds and 235 degrees, so in very good agreement.

All text and images © Duncan Hale-Sutton 2024