Venus on the 24th December 2024

Further to my my previous post I had another view of Venus on Christmas Eve. The weather had been pretty overcast in the lead up to Christmas and so I was pleased to see the planet at all. In fact, I had an additional incentive to make this observation as the BAA had a challenge to observe something on Christmas Day (or alternatively, if the weather was poor, Christmas Eve or Boxing Day). As it turned out Christmas Day and Boxing Day were a wash out, so I am glad I got a clear (ish) window Christmas Eve.

Around 6pm GMT I could see Venus low down in the SW at an altitude of about 11 degrees. There was a lot of thin cloud or mist about, but that didn't matter too much as the planet was bright enough to be seen clearly. I started making another drawing of its phase about 18:04 UT and finished observing at 18:18. This time I made an estimate of the seeing which was AIII on the Antoniadi scale (AIII corresponds to moderate seeing with larger air tremors). Here is the page out of my notebook:-

 

I was again using my NexStar 102 SLT and a 9mm eyepiece. I think this has been a learning experience for me. This time I paid quite close attention to the shape of the terminator and you will see, comparing it to the drawing I made on the 14th, that the cusps of the terminator (where it meets the 'poles') are much more indented than on my earlier drawing. In fact, I made a note about this on my drawing as you can see (it seemed to me that this indented cusp was more pronounced in the north). Taking my drawing again as a measure of the phase, the terminator was found to be 17.5mm from the right edge and since I had drawn my circle to be the same 32 mm diameter as before, this meant that my phase estimate was 17.5/32 = 0.547. 

According to the BAA handbook it was predicted to be 0.590 and so this would mean I had underestimated the phase by 0.043. However, I think there has been a bit of an expectation on my part about what the shape of the illuminated half of Venus should look like. In actual fact, by paying attention to the shape of the cusps I have produced a drawing that is much more like what would be predicted for an illuminated sphere. To aid me in understanding what the predicted shape should look like I have produced a number of drawings on the computer ranging in phase from 50% to 60% in 1% intervals. Here is the one for 59%:-

I think my drawing for the 24th December is accurate in shape for the cusps but is too linear near the equator. This may have been an expectation on my part that the terminator should be closer to the 50% mark than in my drawing on the 14th. In conclusion, it seems to me that perhaps I was underestimating the phase on these two dates.

All text and images © Duncan Hale-Sutton 2025

The phase of Venus 14th December 2024

I have been wanting to get out for a week or two now and see Venus with my telescope since this planet has been more visible in the evening sky. Venus is approaching its greatest elongation east on the 10th January 2025 and it will then be at its furthest angular distance from the sun as viewed from earth. However, this is not going to be a very good apparition because the ecliptic (near to which Venus travels) is going to be low down in our sky.

One of the things I wanted to do with an observation is to estimate Venus's phase as it approaches elongation. When Venus came out of superior conjunction on the 4th June, its phase was full and ever since then its phase has been decreasing and it will reach dichotomy (half phase - equal dark and light) on January 12th 2025. On the 14th December I spotted Venus low in the SSW at an altitude of 5 to 6 degrees. Although there was a bit of intermittent thin cloud I thought it worth getting out my Celestron NexStar 102 SLT and having a look. I didn't bother with a proper set up of this computer controlled telescope but just pointed it in the right direction. Here is a page out of my notebook:-

I used a 9mm Orthoscopic eyepiece that I have owned for about 43 years to get a good view of the planet. The NexStar has a focal length of 660mm and so this gives a magnification of about 660/9 = 73. I had drawn a circle in pencil in my notebook and then at the telescope at around 17.10 UT I drew the phase as I saw it. I had no preconceived notion of what the phase would be and so my choice of shading was as I thought it should be.

I should first point out that the phase is technically the ratio of the apparent area illuminated to the total apparent area of the planet. This is not very easy to measure directly! However, provided that Venus behaves like an illuminated sphere then the phase can be determinded from measuring how far along the "equator" the terminator is and then dividing this by the apparent diameter. I will prove this at some point in another blog entry.

From my diagram the terminator was 18 mm from the right edge and the diameter was 32mm and so I estimated the phase to be 18/32 = 0.563. The predicted phase on this date from my BAA handbook was 0.631 and so the difference was 0.068. Note that with my use of a star diagonal south is at the top of my image but west is still to the right.

I don't think this was too bad. In actual fact many observers underestimate the phase of Venus in an eastern elongation and this is known as the Schröter Effect. I will try and write about this more later.

All text and images © Duncan Hale-Sutton 2024

Recent variable star observations (23rd October, 25th and 29th November)

I have been carrying on with my variable star observations (these are mostly pulsating variables). The evening of the 23rd October was one day before last quarter and the Moon wouldn't rise until 21:11 UT. Astronomical twilight ended at about 18:40 UT. The skies were clear but the transparency wasn't great.

Here are my observations:-

TX Dra, 19:25 UT, chart 106.04, S(2)V(1)K, mag.6.9

AH Dra, 19:40 UT, chart 106.04, 2(3)V(2)6, mag. 7.6

CH Cyg, 20:08 UT, chart 089.04, A(1)V(3)W, mag. 6.7

Z Uma, 20:33 UT, chart 217.02, =C, mag.7.5

On the night of the 25th November, a month later, the Moon was 2 days past last quarter and wouldn't rise until 02:21 UT. Astronomical twilight ended at about 18:00 UT. The sky transparency was average. One of the mistakes I made was to assume that it was still British Summer Time and so I recorded my observation times as an hour earlier than they should have been. Fortunately, I saw my mistake and corrected it. Here are the observations:-

CH Cyg, 18:40 UT, chart 089.04, =A, mag. 6.5

TX Dra, 19:07 UT, chart 106.04, =N, mag. 7.7

AH Dra, 19:15 UT, chart 106.04, =6, mag. 7.8

RW Cep, 22:17 UT, chart 312.02, B(1)V(3)E, mag. 6.7

W Cep, 22:23 UT, chart 312.02, D(4)V(1)F, mag. 7.4

GO Peg, 22:50 UT, chart 103.02, B(3)V(1)E, mag. 7.6

Z Uma, 23:21 UT, chart 217.02, =B, mag. 7.3

A few nights ago on the 29th November it was 2 days before new moon. Astronomical twilight ended about 18:00 UT and the sky transparency was good. Before this observing session I was looking for some new variable stars to observe to add to my roster. The ones in Cygnus below were the first of these. I also had a go at AC Herculis which I hadn't observed since 2023.

AC Her, 19:19 UT, chart 048.4, D(1)V(1)E, mag. 7.8

AF Cyg, 21:51 UT, chart 232.02, =Q, mag. 7.6

V973 Cyg, 22:02 UT, chart 232.02, =F, mag. 6.7

All seen with 10x50 binoculars.

All text and images © Duncan Hale-Sutton 2024

Update on T Corona Borealis

Whilst I was taking pictures of Comet Tsuchinshan-Atlas on the 18th October I realised that the constellation of Corona Borealis was nicely placed for observation as well. We have been waiting about a year now for the eruption of the recurrent nova T Corona Borealis (T CrB) and, as yet, it still hasn't exploded. According to Prof. Bradley E Schaefer the star was predicted to erupt about the 25th May 2024 with an upper error bound of the 12th September. This prediction was based on T CrB entering a "super active" state in 2015 and then entering the pre eruptive "Peltier dip" in the middle of 2023. The problem with predictions is that the stars themselves are fickle and we do not have a good knowledge of exactly what is happening in the processes that lead to an eruption.

I took this image of the constellation of Corona Borealis at 18:59 UT on the 18th October. This was taken with my Nikon D90 with a Nikkor VR 18-105 lens at 75mm. The main image consists of 8x5s exposures (ISO 3200) combined in Photoshop (click on the image to see it full size). This shows the bowl shape of the crown quite well and I have marked the star epsilon CrB near to which the star T CrB can be found. The blue square in the image has been expanded upon in the top left image. This is based on 16x5s exposures at ISO3200 and the contrast has been increased in Photoshop. This inset is at the full resolution of the camera. I have used the BAAVSS chart 025.04 to label some stars and indicate how bright they are in visual magnitudes (the star is always to the right of the green label). The faintest stars being picked up are just about 10th magnitude. The position of T CrB is marked but as can be seen it is only just faintly registering and must have been 10th magnitude or fainter at the time.

Along with the rest of the BAA, I have been continuing to monitor this star as often as I can. My last observation was yesterday (the 25th November 2024) and in binoculars there was still no sign that this star had erupted. At the moment the light curve for this star is still showing that it is fluctuating between 10.0 and 10.5 magnitudes. Of course, you can now find papers that are predicting later eruption dates but who knows what will happen.

All text and images © Duncan Hale-Sutton 2024

Comet C/2023 A3 Tsuchinshan-Atlas

There has been a lot of hype about this comet in the press and, whilst it is good to bring this object to the attention of the public, over doing can mean that ordinary folks get disappointed. This was definitely not a great comet like Hale-Bopp and, although the window when you could just about see it with the naked eye was short, it has put on a reasonable display.

This long-period comet was discovered in February 2023 by ATLAS - the Asteroid Terrestrial-impact Last Alert System. After its orbit had been calculated it was noted that it had also been seen at the Purple Mountain Observatory in China, hence the dual name Tsuchinshan-Atlas. Much has been made of its 80,660 year orbital period around the sun ("your last chance to see this comet for over 80,000 years") but, in reality, four fifths of all comets are long-period, so most are "once in a lifetime".

When this comet swung into the inner solar system and became more visible to us it was a difficult morning object and seen just before sunrise. After solar conjunction the comet became an evening object in the period after October 10th. I had my first good view of it on October 18th:-

This was a single 10s exposure taken on a Nikon D90 with a Nikkor VR 18-105 f/3.5-5.6 ED lens at 18mm (ISO 800 at f/3.5). It was taken at 18:24 UT (19:24 BST) and about an hour and 20 minutes after sunset. The full moon (one day past full) was rising in the east behind me. The comet at this time was in the constellation of Serpens (Caput) and close to the border with Ophiuchus (one of the nearer stars was sigma Serpentis). This view looks sort of south west. You can see that it has a long tail streaming out behind it.

I took a number of such 10s frames and combined them together in Photoshop. Here is a cropped version of the result (16x10s, same settings as before):-

This shows the tail more clearly stretching up towards the top of the picture. I was curious to work out exactly how long the tail was and so I took this picture and made it monochrome, inverted it and increased the contrast.

In this version of the image I have marked the star 45 Herculis whose coordinates are RA 16h 47m 46s, Dec. +05 deg 14' 48''. Knowing that the comet was at position of RA 16h 08m 01s, Dec. +01 deg 52' 23'' at the time the photo was taken, we can determine the angular separation of the comet and this star. This works out to be 10.5 degrees. So the tail is longer than this and by rough measurement it is at least 12.2 degrees long.

Four days later (the 22nd October) the comet had already moved eastwards quite a bit into the constellation of Ophiuchus and I was able to see it with binoculars from my garden:-

This was a combination of 8x10s exposures at ISO3200 taken at the slightly later time of 18:44UT (same camera as before but at 48mm focal length). The image has been cropped. The bright star near the centre of the frame and just below the tail of the comet is sigma Ophiuchi. This field is 12x12 degrees and so the tail is perhaps as not as extensive as it was a few days before.

All text and images © Duncan Hale-Sutton 2024

More variable star observations (5th October 2024)

I have been trying to keep up the momentum of observing and recording variable star brightnesses. On the evening of October 5th it looked like it was going to be a good night as the sky was clear and the moon was only three days past new. However, I had to deal with intermittent cloud which meant periods of waiting until the skies cleared. Moonset was 17:58 UT and astronomical twilight ended about 19:20 UT.

I am going to start recording these observations in a more condensed form to save time. I will use a line for each star starting with the star ID then give the time of the observation in UT, the BAA chart ID, the estimate of the brightness in relation to the reference stars on the chart and the magnitude that this estimate corresponds to. These observations were all made with my 10x50 binoculars.

TX Dra, 20:57 UT, chart 106.04, K(5)V(2)N, mag. 7.5

AH Dra, 21:06 UT, chart 106.04, =2, mag. 7.3

CH Cyg, 21:47 UT, chart 089.04, A(3)V(5)W, mag. 6.8

RW Cep, 22:09 UT, chart 312.02, B(3)V(5)E, mag. 6.8

W Cep, 22:34 UT, chart 312.02, F(1)V(1)M, mag. 7.7

GO Peg, 22:53 UT, chart 103.02, B(3)V(5)E, mag. 7.3

Note that W Cephei is a new star for me to start observing. It is on the same chart as RW but previously I had not been making measurements of it. This is another pulsating variable star (semi-regular, type c) with a range in magnitudes of between 7.02 and 8.50. It has a main pulsation period of 350 days.

All text and images © Duncan Hale-Sutton 2024

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