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Ran my AllSky Camera again from Kelling Heath at the Equinox Sky Camp and on Friday 13th Oct. 2023 and got an even better time-lapse video showing large numbers of geostationary satellites above naked eye visibility.
Have done a crop of the Southern sky which includes the UT clock at the left hand edge: Video can be found at: https://www.youtube.com/watch?v=zOrSYaT4rgQ
For those interested, the geostationary satellites are in a band half way up the screen in the time lapse video. They are at the anti-solar point which starts at the left hand side and moves to the right as the night progresses. At 00.27UT, 45 secs in, about 9 satellites are seen in a swarm with some flaring to mag ~2.
Cheers
MartinHere’s another from Brighton:
https://twitter.com/xejfese/status/1624968248708964353?s=61&t=O7RT9CRRRxtDyujkOiDZwQMartin
Brief blue flash light up a totally clouded sky from StAlbans at 02.59.20, as if distant lightning. Guess that was it?
Martin
Hi Grant,
The reason breezy nights are less dewey is that the warming effect of the ambient air prevents surfaces facing the much colder night sky from being so depressed relative to the air temperature. On still nights surfaces with high emmisivity like plastics and painted surfaces can be several degrees below ambient temperature and well below the prevailing dewpoint. If there is a breeze around it has a moderating effect.I’ve got measurements of a 2.4C depression for a plastic surface on a still night dropping to 1.5C on a breezy night. Radiative sky temperature in UK is typically 30C lower than ambient so there is a strong cooling effect for anything facing it – like opening the freezer door!
Aluminium foil, with its very low emmisivity was 0.9C and 0.2C respectivley on those two different nights making shiny aluminium a great anti-dew blanket!
Martin
Andy Wilson told me that this problem could now be fixed and I changed my name in my profile to remove the Mr. and now I’m back to just Martin Lewis, which I what I wanted. Seems the change in name has stayed rather than reverted as that was a few days ago now.
Worth others trying.
Martin Lewis (previously Mr. Martin Lewis!)
Definitely having dew sitting on the mirror for prolonged periods is bad news if there is any acidity present in the liquid pools but if the water is neutral I don’t think a long dewing is worse than a short dewing. I think the main issue with dewing is that is tends to collect up loose surface debris into rings and spots – these agglomerations of particles are then no longer loose and become stuck to the surface causing scattering and loss of contrast. The collecting action locally concentrates up any agressive debris on the surface increasing its likelihood of attack of the surface.
Fans to blow on the surface of the mirror to speed up evaporation will only work if the air being blown over the mirror is lower than the temperature of the mirror and blowing ambient air over a mirror below the dew point will just make matters worse.
Some observatory owners do have electric dehumidifiers in their observatories and these can be triggered on relative dew point or just switched on after a session to dry everything off.
Martin
I suck and blow!
My 18″ mirror is in a square mirror box and I have a soft surround to the mirror with 4 small fans one in each corner to pull air down the tube during cool down prior to imaging. Meanwhile I blast the middle of the mirror rear with a 100mm fan which has a large baffle around it so the air get funnelled raidally across the mirror. This cools the primary at the maximum rate and faster than if I were sucking air past the back. I can control the small fans separately from the main primary fan and both sets are speed controlled. The idea was that I could switch off the main fan at the start of an imaging session but still have the small fans sucking down the tube. Trials showed little benefit in doing this and generally I give everything an hour’s blast and switch them all off during imaging. Blowing during hi-res planetray imaging is definitely is a bad idea from my trials.
If the scope or mirror is below the dew point, condensation will form on it, so you either have to warm the scope and mirror or decrease the dew point of the surrounding air. Don’t think there are any other options. You could bag the whole scope and put sachets of dessicant in the bag to drop the moisture in the surrounding air? You’ll get through a lot of dessicant, though it is rechargeable through heating. Or put an electric dehumidifier unit in the vicinity.
Good luck
MartinTo make this clearer I have cropped and rotated the video from the Sunday night (10th Oct) and boosted the brightness. Multiple flares occur across the mid line of the video as the anti-solar point moves across the southern sky from L to R. This runs from 22.18UT to 1-13UT. You can see the video here: https://vimeo.com/640645977
Martin
Thanks Grant,
These are much brighter than 5th magnitude though. Some were definitely 2nd magnitude.I guess they would be in the Earth’s shadow at the anti-solar point that’s maybe why they are brighter 45 mins before or after.
Martin
Hi Peter,
It’s good to have a convention to make images easier to compare images and can’t see a reason not to stick with the existing arbitary one rather than change it after several centuries. Jupiter with a GRS at the bottom and a Mars with Syrtis Major at the bottom – to me they just don’t look right.It is arbitary whether it has been chosen to be north up or south up but south up is the existing astronomical convention. In the northern hemisphere that’s the view in an inverting telescope but from the southern hemisphere that is the view in an non-inverting set up. There is no such thing as the right way up or wrong way up just the conventional way up and the unconventional way up.
I am intruiged by your comment that you see visually a view with North at the top when you view through an SCT with no diagonal. Surely an SCT with two mirrors should give an inverted view. I though it was only through a diagonal that you would get a non-inverted view but it would be mirrored L-R.
Cheers, Martin
Sorbothane is good stuff in the right application but here won’t it make the mount very sloppy?
There is a great application guide for Sorbothane here: https://www.sorbothane.com/Data/Sites/31/pdfs/product-guides/Sorbothane-EDG.pdf and an even more useful design calculator here: https://www.sorbothane.com/Data/Sites/31/edg/vibration-calculator.html Generally what is important is to compress the Sorbothane by 15-25% for best performance – so you pick your area to give you that compression for your given load.
Martin
What an interesting project Tracy. Very keen to hear how you get on. Might be able to do some EDX elemental analysis along with our next sample run in a few weeks if you can wait that long. Not sure on interpretation though. EDX will tell you what elements are there in the first few microns of the skin.
Martin
Wanted to add a comment to POTW but after pressing submit. It said ‘blank comment ignored’ and nothing is showing.
Martin
I commented on that same image by Martina and liked it too but that info has gone too. As Paul says might be indicative of other missing info. Great job otherwise Dominic.
But will animated Giffs work now??
Martin
I commented on that same image by Martina and liked it too but that info has gone too. As Paul says might be indicative of other missing info. Great job otherwise Dominic.
But will animated Giffs work now??
Martin
Image taken at 20.22UT last night in difficult conditions with Jetstream troublesome, shows Solis Lacus at the limb with significant dust above it. See; https://britastro.org/node/25060
Cheers
MartinHi,
Why don’t you determine it empirically — as presumably it is the position where aberrations are minimised?
Star test either side of a know positions further and further out from location of max in-travel. Use a digital video camera to capture the out-of-focus start images and allow you to average them and you’ll have a record of the intra and extra focal images for each mid-location. Best position is where the intra and extra focal images are most similar to each other.
Cheers
MartinYes, sage advice David – alarm bells were ringing in my ears as I read it. Didn’t want to end up in the small claim court myself!
Martin
