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Paul, I know you are after various editions of Norton’s which I look out for, but none so far. I’ll see what else I’ve got.
James
Back when I was an undergraduate another member of OUAS had a copy of “Webbs Atlas of the Stars”. It disappeared and the erstwhile owner regretted it greatly.
I have always wanted a copy of my own but they are almost unobtainable now. When they do appear on the market the prices are ridiculous — several hundred USD/EUR/GBP — and I refuse to pay that much. I own a good number of atlases, old and new, for which I have paid much less than that.
If anyone has a copy of Bečvář’s Australis at a reasonable price I am also interested. His atlases are already in my possession and I have a spare copy of Eclipticalis if anyone is interested.
I’ll be there with a load of secondhand books for sale, so bring your money.
I am often in the market for old atlases, especially editions of Norton’s not yet in my collection. Don’t know if this will influence your choice of books to bring.
Paul
Measuring stellar proper motions has been possible for amateurs for a long time now, though we will not reach Gaia levels of accuracy.
In particular, I really must update my track of Barnard’s Star with images from this year. Ok, that’s an extreme case but proper motions greater than, say, 100mas per annum should be fairly easy to measure over the course of a year or few.
The pipeline I use is MaximDL for taking images; local astrometry.net using the Gaia catalogue to put a WCS on each sub; SWarp for stacking if required; and then APT for photometry (my primary interest) and initial astrometry (if desired). The source list fed into APT contains Gaia positions and its output includes substantially sub-pixel precision on the stars’ centroids, in both pixel and sky co-ordinates. That’s good enough for me (and I repeat that my primary interest is in photometry rather than astrometry). Perhaps I could, and should, try harder to achieve ultimate accuracy in astrometrical positions.
Paul
<p class=”wp-dark-mode-bg-image”>A test would be to take images with the telescope rotated to different angles (but with the camera orientated the same relative to the horizon). If it is atmospheric refraction the red and blue areas will always be top and bottom relative to the horizon. If it is the telescope, they will move to different angles relative to the horizon
<p class=”wp-dark-mode-bg-image”>Cheers<br class=”wp-dark-mode-bg-image”>
RobinGood point. I wish I had thought of that.
At what altitude was the moon at the time?
The atmosphere acts as a prism and deviates red and blue light differently at different altitudes. The effect is most apparent where the air is thickest — at low altitude.
https://en.wikipedia.org/wiki/Atmospheric_refraction covers the phenomenon but only slightly and could be greatly improved in my opinion. Searching on “atmospheric dispersion corrector” will produce more information and a fair description appears at https://astronomytechnologytoday.com/2017/07/06/atmospheric-dispersion-corrector/ but the available information is far from satisfactory in my opinion.
Paul
1. One-word answer: temperature. The smaller the gravitational field gradient the less likely a virtual particle pair (not restricted to photons by the way) is to be split into real particles and the lower the energy carried by each. As photons have zero rest mass there is no lower limit to their energy, which corresponds to no lower limit to the temperature of the BH. All sufficiently massive black holes have a very low temperature. A solar mass BH, for example, has a Hawking temperature much much lower than that of the cosmic background and is absorbing those photons, thus slowly gaining more mass from them than it is losing from Hawking radiation. The hypothetical observer would see the CBR as being much much more intense than the Hawking radiation which would be swamped completely by the background.
2. There is no good theory of quantum gravity as yet. The naive calculation is almost certainly wrong. Further, Hawking radiation has yet to be observed because all known black holes are far too massive to emit significant levels of radiation.
I love the 112 authors not listed. How many words is that per author?
Is this going to happen whenever the LSST consortium publish?
Astronomy is now reaching the point particle physics reached about fifty years ago.
Big collaborations collecting vast amount of data which requires enormous amounts of computation to convert that data to information.
It is getting that way in biology. I’m a co-author on a few genetics papers published by the Flybase Consortium which have numerous authors, though admittedly not over a hundred.
Welcome to the new world.
<p class=”wp-dark-mode-bg-image”>Y
<p class=”wp-dark-mode-bg-image”>As for all this talk of molten metals: don’t try this at home kids.The important word here is “kids”.
I very much doubt that anyone here is a kid,
5, Make your own. < £20.
If you don’t fancy the idea of pouring lead I’d make one for you but you are in the UK and I am not.
Paul
P.S. Concrete would work as well. Messier, not as dense as lead and takes longer to solidify, but not as hot when wet.
I needed an extra weight for my Meade.
An old metal paint can, a kitchen stove and some scrap lead worked wonders. A wooden stick, well soaked in water, made a central hole which needed only slight tidying before the weight went over the shaft. No fastening screw so it is held between two of the original weights which can be fixed in position.
Acquiring scrap lead is not that difficult.
Cost me nothing but a bit of butane for the stove and 30 minutes of my time. I even found the can discarded on a building site.
I am not a mechanical engineer, but wouldn’t the thread give way before the body of the bolt? I’ve seen far too many stripped threads in my life.
Hi Callum,
It looks like another of my posts went astray, this one about 3I/ATLAS. Could you see if it has been wrongly marked as spam please?
This behaviour is very annoying. Can it be improved please?
That is roughly what I was suggesting.The idea came to me when I remembered the image of Halley’s comet which was released shortly before the comet reached aphelion. The stars were subtracted and what remained stacked on the motion of the comet. IIRC, C1/Halley was 29th magnitude at the time.
The idea is testable using images of a star field which is easily measurable before removing all but one of the stars. See whether the before and after measurements are comparable. Repeat with different stars removed and with different fields.
It’s a shame I’ve so little spare bandwidth or I would try it myself with some of my planetary satellite images — of Amalthea, say.
Added in edit: Ah, my earlier response to Nick contained that idea with the suggestion that DAOPHOT’s computed background images be stacked and measured. I know it was posted because I subsequently edited it. Hmmm….
Second edit: Callum rescued it from spam purgatory and it now appears above. Thank Callum.
Paul – I’m pretty sure that the scatter is due to faint stars in the aperture since this is a very crowded field. I think it is far to early to say anything about the lightcurve of this object but the more observations the better. I have used DAOPHOT and it can be very good but I’ve not been able to get it to work reliably with moving objects.
Just a thought: have you tried using DAOPHOT on each sub to remove the stars and then stack the remaining sky background? All that should be left are the very faint objects.
Not suggesting it will give results which are any better but it may prove an interesting experiment.
<p class=”wp-dark-mode-bg-image”>I’ve been doing some astrometry on 3I/ATLAS and have been surprised how much scatter in the magnitude that I’m getting day to day. The plot of magnitudes from MPC astrometry data also shows a huge scatter. This data doesn’t have a consistent photometry aperture or filtering but, for most observers at the moment 3I/ATLAS is a point source so it is surprising. The scatter may be due to measurement errors in the crowded star field but it is worth making estimates of the magnitude if you can.
Might the scatter arise in large part from the multitudinous fainter field stars which are too faint to show up clearly in the images but the photons from which will create a very noisy sky background. The noise will add both to the counts at a given a pixel and will vary strongly from pixel to pixel.
Have you tried PSF-fitting photometry, using DAOPHOT for example? It would be interesting to see whether you get significantly different results. DAOPHOT is famous for working well in crowded fields. It is a shame that using it is often a fiddly pita in practice.
It is interesting that 2I/Borisov was definitely cometary and it looks like 3I/ATLAS is as well. 1I/Oumuamua was not but it did have anomalous nongravs which implies it must have been comet-like.
It is clearly an alien space ship. 😉
