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Thanks Jack, I’ll put it in the next E&T News. But I’ll keep it separate from the cats, as it would poison them.
All the images in this set showed the interesting terminator irregularity in the S hemisphere. It is clearest in the first image, R from 02:38, and I have given an enlargement of that one. Comparing with other published images from the same night, I believe this is due to straight N-S ranges of cloud over the Tharsis Montes casting shadows. The irregularity seen here is a combination of a bright line of cloud catching the light, and its shadow preceding, with another high bank of cloud to S just going over the terminator.
Thanks David, that is very helpful. Is your email still the Freeserve one? I’ll get in touch with further details.
Don’t try contacting the first website that Daryl quotes. People who have been involved with BAA for a while will know why.
The bolts that are supplied with the telescope are about 2″ long, smooth-shanked and threaded with a ¼” Whitworth thread in the top ½”.
They work by the thread engaging with the mirror cell while the unthreaded section passes through the hole in the back of the scope and the knob clamps tight. Owing the varying mirror position at different focus points, I am not sure if they would succeed in in locking the mirror at any point in its focus range, or not.
Assuming they do, and assuming you are using one optical configuration with camera at a fixed distance out in a Crayford or similar focuser, I don’t see why you should not lock the mirror in position with these screws after you have established the approximate focus point for the mirror, with the Crayford in the middle of its range, to give a bit of temperature compensation around that point. However, I have not tried this. I tend to do my critical work around the same part of the sky, the meridian, so the collimation does not change much.
BAA member John Sussenbach in the Netherlands had good conditions, and produced this lovely video. From my location it was too cloudy.
https://youtu.be/8SS-yjY5WakSo it used to work and now it doesn’t, you are saying? There is a clear difference between the images it gave more than 18 months ago and now, even allowing for the decline in sunspots?
All solar equipment does degrade with time, and always needs servicing eventually. If there’s no detail, then one of the filters inside is not performing correctly, and likely needs replacing, which can only be done by Coronado.
I think you are quite right, Peter.
I think when thinkers in all different disciplines are separated from their usual colleagues, usual influences and the peer-pressure that results in people grouped together thinking thinking similarly, original and useful thoughts are very likely to result. Also there is likely to be less distracting day-to-day administrative activity, enabling deeper thought.
I recall the comment of Joseph Haydn, about his period spend at the court of Price Esterhazy in Bohemia, that he was isolated from all the influences he had had in Vienna, and so he was forced to be original, writing his best music there.
I have also been spending a lot of time in the shed at the bottom of my garden, waiting for inspiration to strike.
I’m not sure what Jack thinks is the ‘clear and correct’ answer, as he didn’t say.
This is a matter of social convention, not calculation. No-one was actually counting decades after the beginning of the Common Era (the supposed year of the birth of Christ according to (probably erroneous) mediaeval scholars) in the years immediately after. Therefore there is no continuity here and no reason why we can’t regard the first decade of the Common Era as having only 9 years, or extending from 1BCE to 9AD.
A decade is generally regarded as a grouping of years having the same three initial digits. Therefore the new decade has begun.
An excellent meeting that reminds people the BAA is the premier astronomical society for the whole of the UK.
And I think a special mention is due to the member who travelled furthest to get there: Barry Adcock and his wife made the journey from Australia. He then went to Geneva for the European Planetary Science Congress, where he presented a poster, that he showed me in Armagh, of his work on multispectral IR imaging of Jupiter, done with his amazing home-built 12″ refractor.
Congratulations to Meetings Secretary Hazel Collett, and the others involved in the organisation.
Now we need to solve the mystery of why Armagh Observatory has an orrery that shows 5 moons of Jupiter, but doesn’t show Neptune, which was discovered long before Amalthea.
Thanks for that Bill. I hadn’t seen that Dial-a-Moon site before. It is very useful.
Indeed it shows exactly this effect, produced by the far wall of Bailly catching the light while craters to either side just beyond it, Hausen and Le Gentil, are totally dark. The effect was particularly striking with the field of view on the camera being only about 2.5 Bailly diameters wide. It’s more explicable when seen in the wider view. I also viewed it the other way up (I always invert my images to make them celestial N up for publication), and it seems to look, for psychological reasons, more strange when viewed that way: almost like thew apex of a house roof – see below.
The familiar Moon can certainly throw surprises.
Yes I think it would generally be regarded as best practice to do any data summation (i.e. stacking) before any data chopping, as it is the summation stage that clarifies what is data and what is noise, and therefore doing it the other way round risks throwing away data.
In planetary imaging in twilight or daylight (with filters) we often chop off the sky background level to increase overall contrast, but I do this after sharpening.
But another (odd-sounding) technique which I think does have some legitimacy here is to attempt to guide the way Austostakkert! stacks the images by using as a reference frame an image that has been manipulated, by masking, to be the shape the planet is expected to be. I have seen another other observer get good results on Mercury by this method.
In Berkshire I would have thought the overwhelming effect would be the switching off of lights. I notice this in London: it is much darker after midnight, though none of the surrounding local authorities switch their street lights off.
Yes in theory the airglow, caused by ionised molecules, would have a decay through the night, but, as others have said, it’s not going to contribute much for us.
I’ve not heard of this technique before, but it’s an interesting idea. I’m not sure why it would have much effect on the sharpening, as you are just eliminating some random background noise. I’d be interested to see examples of images processed with and without this step.
David
Director, Equipment & Techniques Section
Of course Mark also collected and restored a large collection of instruments manufactured by the Hysom brothers’ firm AE between the 1960s and 80s. This included a 10″ Relay-lens Dall-Kirkham Cassegrain that I used to use (I described this instrument in JBAA 2007 April) that was also reputedly part-made by Dall. I don’t know if he still has this curious collection.
There seem to be two issues here: weight (back problem) and setup time.
These are common problems. I deal with them in my book ‘Setting-up a Small Observatory’ (Springer), and we’ll deal with them again at the Equipment & Techniques Section meeting on 17 November.
I think you have 6 general choices, which address, or not, the two issues, in different ways:
- Leave the tripod and wedge outside, polar aligned, cover it with some sort of cover, and just move the telescope and other equipment in and out each night (may not address weight problem)
- Leave the telescope and tripod outside and cover it with some sort of cover or box, either flexible or rigid, that is completely removed when you observe (might address both problems)
- Build a proper observatory (addresses all problems in the long term, but may be difficult or expensive)
- Get a system that breaks down better into lighter components, maybe tripod, German equatorial mount with dovetail fitting, and optical tube (may not solve setup time problem)
- Get a smaller telescope (solves most problems, but not good for planets)
- Get a tracking alt-az or Dobsonian system (may not solve weight problem)
Damian Peach seems to leave his C-14 outside most of the time, just covering it over with a fabric cover, and it survives. In my experience this method results in corrosion, however, and of course you’ve got a big security problem. You still need to disconnect and take in all the camera etc. More of a proper shelter or box, such the one Richard Miles built, is better. This kind of solution, if well done, allows you to leave everything outside, including cameras, power supplies and wiring, and this saves an immense amount of time.
Nothing really beats an observatory for time-saving and back-saving convenience, and at the meeting on 17 Nov I’ll be describing a ‘An observatory from a £100 shed’.
But going back a stage, without building anything, you do mention polar alignment taking ‘impossibly longer’. Imaging planets does not require very accurate polar alignment, so I wonder if you are making too much of a meal of this. Increasingly also people are using the new CMOS-based cameras from companies like ZWO and Altair to do deep sky imaging in a more ‘planetary’ manner, using stacks of short exposures (1-10s). Then they really don’t need accurate polar alignment at all. In fact planetary imaging, and this sort of short-exposure imaging of brighter deep-sky objects, is possible with the tracking alt-az or Dobsonian system I mention as option 6.
There’s a lot to consider, and in the end only you can tell what your best convenience/performance/expenditure compromise is.
David
Director, Equipment & Techniques Section
The night after my previously reported observation, on February 22, I managed to get my C-5 (127mm SCT) mounted where I could get Sirius with it. I first had to cut down much of a giant weed in my elderly neighbour’s garden, that was in the way. I seem to do most of my gardening at night. Anyway, despite careful collimation, I certainly could not see Sirius B. There is no possibility with a telescope that gives such a messy diffraction pattern as this. But using a refractor of the same aperture, particularly a relatively long focal length one, would be a very different proposition, and I’d like to someone give this a go on a number of occasions from the UK.
I looked for the first time tonight for the pup from my observatory in Edgware, Outer London, Lat. 51N. I did not read the Observers’ Challenge and deliberately did no research in advance to tell me where it should be, in terms of PA, so as to get an unbiased result.
I looked for the Pup at culmination with a C-14 at 300x and 480x. I tried normal monocular observing, I tried using two eyepieces with a Denkmeier binoviewer, and I tried the addition of a dispersion corrector, set to correctly remove the spectral dispersion for the altitude. In all cases I could clearly see what I thought was the Pup, and I estimated its PA as 75 deg. by eye. It was easiest to see at the higher magnification, but once seen with that, could be seen at the lower magnification as well. It could be seen as well with one eyepiece as with two, but less well with the dispersion corrector: I imagine the the loss of light from the prisms in the corrector negated any benefit of concentrating the light better, but with the binoviewers, loss of light was countered by the benefits of binocular viewing.
My C-11 is always used for CCD imaging and has a Hyperstar system in place, so for visual purposes my next telescopes down in size are a 10″ Newtonian and a C-5, but they are on a mounting in a location from which Sirius is obstructed by a fence, so I could not try to see it with them.
I did try with my Celestron 100mm f9 ED doublet refractor that is mounted with my C-14. Using a magnification of 346x, having identified the Pup through the C-14, I intermittently thought perhaps I could see something at the correct PA, as an enhancement of the diffraction rings, but at other times I thought not, and I could not convince myself ultimately.
So my conclusion is that from London the Pup is very clearly visible with 356mm aperture, and would certainly be visible in a smaller telescope – maybe, at a guess, down to 200mm.
It’s now occurred to me that as I have my C-5 (127mm SCT) mounted on a dovetail, I can move it to the mounting I have the C-14 and 100ED on, so I could test the C-5 on the Pup in future. Past experience has been that the C-5 is less effective on doubles than the 100ED, because of more light in the diffraction rings due to the large central obstruction, so, despite giving a brighter image, it seems unlikely it would show the Pup.
I long ago decided as policy always to keep my C-11 in Hyperstar mode permanently, and the secondary resides unwanted in a drawer. It’s such a faff getting the Hyperstar alignments just right, as you say, it’s not worth going back to long FL imaging after prefecting it. Better to get another telescope – good 2nd hand C-8s go pretty cheap – and swap them on the one mount.
