TX and AH Dra, CH Cyg, Z and RY UMa on the 30th October 2022

We had some more clear weather here on Sunday the 30th October. The moon was nearly at first quarter but it would set at 20:04 UT. The sky transparency wasn't great but I decided to go ahead with my observations anyway. The constellation of Draco was in the west but still high enough in the sky to make estimates of the semiregular (Srb) variables TX and AH Dra.

Beginning with TX on chart 106.03 with my 7x50 binoculars I could make out star P at visual magnitude 8.4. TX was fainter than star K (=7.0 mag.) and star N (=7.7 mag.) but brighter than P. At 21:16 UT I saw that TX was much closer to N in brightness than star P, so I estimated it at 1 point from N and 3 points from P (i.e. N(1)V(3)P). This put it at magnitude 7.9 to 1 decimal place.

I then moved on to AH Dra which is south of TX. At 21:40 AH was fainter than star 1 (=7.1 mag.) but brighter than star 8 (=8.4 mag). In fact it was probably middle way between these two stars and this was confirmed by comparison with star 6 (=7.8 mag.). So my estimate was 1(1)V(1)8 which made AH visual magnitude 7.8 to 1 d.p.

Whilst I have been writing up this observing session I have noticed that there is a new chart for TX and AH Draconis. Chart 106.03 has now been redrawn and is now 106.04. The only difference that I could spot was that the star labelled 1 is now magnitude 7.0 rather than 7.1. I will use the new chart in my next session.

Cygnus was also reasonably well placed so my next target was the ZAND+SR variable star CH Cyg. This was easy to estimate as its brightness indistinguishable from star A and was thus magnitude 6.5.

Finally, the constellation of Ursa Major is beginning to rise again about 11pm having swung round under the pole, so I could have a go at Z and RY UMa. At 22:34 UT Z UMa was brighter than star D (=7.9 mag.) but was equal to B meaning that my estimate was magnitude 7.3. At 22:43 UT RY UMa was fainter than star 1 (=6.7 mag.) but was brighter than star 4 (=7.7 mag.). In fact its brightness was indistinguishable from star 2 which made it magnitude 7.4.

All text and images © Duncan Hale-Sutton 2022

Partial Solar Eclipse 25th October 2022

We had a partial eclipse of the sun on Tuesday 25th October. From our location near Norwich first contact with the moon was to begin at 10:07, maximum coverage was to occur at 11:00 and last contact at 11:55 (all times BST). I had a flu jab appointment at 11am and so I didn't have much time to set anything up. In the end I decided to use my 8x24 binoculars to project the image (twice!) onto a sheet of white paper. The first image I took was at 10:39 and the last at 10:47. The best of them was this image at 10:45 (15 mins before maximum):-

I quite like the fact that this looks like two eyes looking down. Looking at this image I think that the "bite" taken out of the sun is much less than 25% of the total area of the disk. To see this imagine dividing the sun into four equal quarters of cake. The bite can be seen to roughly sit in one of those quarters but it by no means covers the whole quarter. However, I do reckon that the bite covers more than half of that 25% (i.e. more than 12.5%). So perhaps 15 or 16%. I must try and calculate it. London was predicted to be 15.2% at max.

I have now (18th November 2022) done some work on calculating the obscuration (the percentage area of the sun that is covered by the moon as it is called). Have a look at this diagram below:-

The shaded area represents the area of the sun that is eclipsed by the moon. I have assumed that the moon and the sun appear to be the same angular diameter on the sky. I have found that the percentage obscuration is given by 100 (w - sin w) / pi where the angle w is in radians. To find w you need two measurements; the length of the chord PP' (which we can call l) and the diameter of the sun (which we call d). Then w = 2 arcsin (l/d). 

In the above picture of the eclipse I chose the left-hand projected image which was more well defined and circular and measured l to be 209 pixels and d to be 311 pixels. This gave the obscuration to be 15.2%. But I think this is a coincidence that it is close to the London value!

All text and images © Duncan Hale-Sutton 2022

AC Her 18th October 2022

On Tuesday the 18th October we had clear patch in the early evening when I thought I could get some variable star observing done. The moon was at last quarter the day before and it wasn't due to rise until about 10:52 UT. At 19:03 UT the skies were clear and there was virtually no wind. I was hoping to observe more than one star but by 19:30 UT it had clouded up!

However, I did get a look at AC Herculis. Looking at BAAVSS chart 048.04 at 19:15 UT with my 7x50 binoculars I could see star E which has a visual magnitude of 8.2 so my limiting magnitude was fainter than this. At 19:20 UT AC was brighter than this star and also star D (at magnitude 7.4). However, it was fainter than star C (mag. 6.9) but not by much. So at 19:26 UT my estimate for AC Her was that it was 1 point from C in brightness and 2 points from D, namely C(1)V(2)D. This put it at magnitude 7.1. This was in good agreement with other observers from the BAA.

All text and images © Duncan Hale-Sutton 2022

The Sun on the 25th September

Over a week ago I had another go at projecting the image of the sun using my Celestron NexStar 102SLT. I used much the same set up as before, projecting the image onto white paper. Here is the image taken at 10:02 UT (using a Samsung Galaxy A21s phone camera):-

North is at the top and East is to the left. I have added the Active Region  numbers as they have been officially allocated. I would have preferred to have determined the East-West drift line myself but there wasn't time before cloud obscured the view. Instead I compared my image to that of the Solar Dynamics Observatory taken a few hours later at 13:45 UT (Courtesy of NASA/SDO and the AIA, EVE, and HMI science teams):-

 

To get how much my image had to be rotated by compared to the SDO image I examined both images in photoshop. By measuring the angle between the vertical and a line drawn between the same two sunspots on both images I was able to determine the difference between them. I came up with differences of 44.1, 44.6, 44.7 and 44.9 degrees, giving an average of 44.6 which is how much my image needed to be rotated by to get North at the top.

My image compares quite well with the SDO image. There was one active region to the far right of the SDO image that didn't show up in my image because it contained sunspots that were so small.

I have been wanting to try and quantify the activity of the sun and one way to do this is to calculate the Relative Sunspot Number or R number. The method for this is described in this BAA guide. It can be seen on both images that sunspots appear in groups (or active regions). If the number of groups seen is G and the total number of sunspots in all groups is S then R is 10*G+S.

A couple of things to be aware of is that a group is counted as separate from another group if its centre is more than 10 degrees away from the other group's center. However, it isn't that easy to quantify how much 10 degrees is on a 2D image of a 3D sphere! We can get an idea of how much it is by drawing on the sun's image a diameter from East to West and then a radius that at an angle of is 10 degrees to this line. The arc along the sun's edge subtended by this is then a guide to how far 10 degrees is on the surface.

Another point is that sunspots have a dark umbra and a lighter penumbra and sometimes several spots are linked by a contiguous penumbra. In counting sunspots it is the darker umbrae that should be counted rather than a "spot" linked by penumbrae.

Given all this I think from my image AR3110 has 4 spots, AR3107 has 6 spots, AR3105 has 5 spots and AR3108 has 2 spots. That is 4 groups and 4+6+5+2=17 spots. So R=10*4+17=57.

I did find this confusing because clearly a better image like the SDO one has much more detail and so many more spots and a few more groups can be counted. However, I have learned that R is a relative number that reflects the observer's estimate. It is therefore important for observers to use the same methods/equipment) each time.

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

Jupiter

A few days ago on Monday the 19th September we had some very nice dark skies and I thought I would try to observe Jupiter which is approaching opposition on the 26th September. I decided to use my 5.5 inch Orion OMC-140 Maksutov-Cassegrain mounted on a Sky-Watcher HEQ-5 mount. I didn't bother to set up the drive properly so the image of the planet drifted in the eyepiece.

At about 11pm BST I began using a Celestron 25mm eyepiece which gave a magnification of 80x as the scope has a focal length of 2000mm. It was nice to see all four Galilean moons and some details on the planet surface. Rather than trying to photograph what I could see I made a drawing:-

In this picture south is up and west is to the left. The moons were nicely displayed with Io closest to Jupiter and then, with increasing distance from the planet, Europa, Ganymede and Callisto in that order. This was verified by looking at the BAA Handbook. On the planet itself the Northern Equatorial Belt (the much darker thicker line) was obvious but the detail of the southern features much less so and my impression was of three faint lines as drawn. I swapped to a 20mm Erfle lens which gave a slightly better view (x100) whilst I drew the details.

I wish I could have seen more details on the gaseous surface but I think a 5.5inch objective just isn't big enough. I did swap to a 9mm orthoscopic eyepiece that gave a magnification of x222 but this didn't improve the detail, though I did look very hard. The seeing was pretty good and there were longish periods when the image looked stable and in focus. I finished observing about 40 minutes later.

All text and images © Duncan Hale-Sutton 2022

AC Her, CH Cyg, TX and AH Dra

We had a better night for observing last Saturday, the 17th September, when the sky cleared in the earlier part of the evening. Drifting light cloud was still a bit of an issue but not as much as on the 5th. Twilight ended just after 9pm BST when I started observing and the moon wasn't due to rise until 10:11pm BST it being at last quarter.

It was earlier enough that I could get a decent observation of AC Herculis before it began to head over to the west. At 19:52 UT I could make out star E on chart 048.04 and so my limiting magnitude was fainter than 8.2. At 20:09 UT I estimated that AC was about equal in brightness to star D which made it magnitude 7.4.

I then went on to look at CH Cygni which lies in the wingtip of Cygnus the swan and overhead at this time of the year. At 20:29 UT I estimated that CH was about equal in brightness to star A on chart 089.04 (pdf) which made it magnitude 6.5. I think my estimate may have been 0.2 to 0.3 magnitudes brighter than other BAA observers who saw this star on the same night.

I moved round to the other side of the house to have another go at TX and AH Draconis. At 21:11 UT I thought that TX was brighter than star N (mag. 7.7) on chart 106.03 but only somewhat fainter than star K (mag. 7.0). So my estimate was that it was 2 "points" from N and one from K making it magnitude 7.2.

Finally, at 21:28 I estimated that AH Dra was about midway in brightness between star 1 (mag. 7.1) on chart the same chart and star 6 (mag. 7.8) making it magnitude 7.5.

All text and images © Duncan Hale-Sutton 2022

TX and AH Draconis

It has been a difficult time to get any observing done recently what with the cloudy skies we have been experiencing of late. I tried a couple of times on the 19th and 31st August to do some variable star observing but cloud just kept getting in the way. I had some more success over a week ago on the 5th September and was able to get observations made of TX and AH Draconis. At the time when I was observing, the moon was 2 days past first quarter but low in the sky to the south. There was a little bit of light cloud but this didn't really make an impact until after 11pm BST. There is no problem with twilight now after 10pm BST when I started observing. These stars in the constellation of Draco aren't far from the star Eta Draconis which was still high in the sky to the west.

At 21:38 UT I could make out star P on BAA chart 106.03 with my 7x50 bins. This meant that my limiting magnitude was fainter than 8.4. At 21:46 I estimated that TX was marginally brighter than the star N (=7.7 mag.) on the chart but fainter than K (=7.0 mag.). So my estimate was K(2)V(1)N (one "point" from N but two "points" from K) which made it magnitude 7.5 to one decimal place.

Moving on to AH Dra I observed at 22:01 UT that this star was brighter than star 8 (=8.4 mag.) on the chart but fainter than star 1 (=7.1 mag.). In fact, it was much closer in brightness to 8 than it was to 1, so my estimate was 1(3)V(1)8 which made it magnitude 8.1 (to 1 d.p.).

This last observation was a bit rushed as I could see a bank of cloud moving in from the south which would end my night. However, I don't think either of these observations are in too much disagreement with other observers from the BAA.

All text and images © Duncan Hale-Sutton 2022