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<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. 😉
I also support this, having imaged several of the Palomar GCs.
While on the subject of GCs it would be nice if one could tag extra-galactic GCs (for example, Mayall II) with both “globular cluster” (term not yet included in the dictionary) and the host galaxy “M31” (already present). Would make finding images of GCs much simpler.
Of course, the same approach would be helpful for other classes of objects, such as “double star” and “planetary nebula”.
Paul
Back when I was a teenager we saw an Elephant Hawk Moth caterpillar walking along the garden path. It was the size and shape of a perambulatory chipolata.
As it was clearly close to pupation we kept it safe until it hatched and then released it.
That was in Derbyshire. Privet Hawk Moths were relatively common on the Oxon/Bucks border. No idea whether they still are.
Richard: the Elizabethans were well practised too and, with the advantage of an additional century of technological development, were able to do so on an industrial scale. Remember DDT? Remember the Camelford incident which is well described in https://en.wikipedia.org/wiki/Camelford_water_pollution_incident where not only were people left with aluminium deposits in their brain, lead from piping was also leached into drinking water? How about tetraethyl lead added to petrol?
Incidentally, and speaking as an ex-chemist, the dangers of Pb poisoning are almost universally misunderstood. Organic lead compounds, such as PbEt_4_ are really, really nasty. A few milligrams will kill you and quite rapidly too. Soluble inorganic lead compounds do pretty nasty things to the CNS. Insoluble lead compounds are arguably helpful — a coating of lead sulphate or carbonate on the inside of lead water pipes which is naturally produced in hard water districts prevents soluble lead compounds leaching out. Metallic lead is virtually harmless, unless injected en masse into the body at high velocity. Many people live for decades with several grams of Pb inside them, especially where the location of the bullet makes surgery to remove it a markedly higher risk than to just let it be.
I’m sure that you as another ex-chemist are well aware of the content of the previous paragraph.
Paul
