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I have that book but it never occurred to me that the lunar maps were the ones under discussion. They are indeed beautiful and practical, not that I ever look at the moon through a telescope any more.
Added in edit: I forgot to mention that I have the French translation.
Andrew has turned down my offer of free hosting for the BAA, including power, internet and tech support.
The pad is still available, either to a private individual (in which case I would charge the same as Kevin now pays and would provide the same service) or for at most a peppercorn rent to the BAA if the observatory were to be used for charitable purposes.
We’re flying out in 36 hours time. LP isn’t as easy to get to as GC or TF, I fully agree, but it aint that difficult either. There are direct flights once a week from MAN and LGW. On this occasion, all the flights LGW->SPC were fully booked. From where we are in Cambridge, STN is a much nicer option anyway, so we are taking Ryanair STN->LPA and then Binter for the LPA->SPC hop. Really not that difficult.
Don’t know whether it is relevant, but I have a spare concrete pad in La Palma. It’s 4m square, around 20cm thick and has been used by a European university physics department as the site of a robotic telescope. Power and ethernet are laid on but there is no other infrastructure right now. A Google maps image is available at https://www.google.co.uk/maps/@28.6419037,-17.8677037,123m/data=!3m1!1e3 which shows the orange circle painted on the slab. To its left is Kevin Hills’ robotic observatory and to its right is mine.
Musk has already stated that they’re looking at darkening the satellites. Unfortunately, painting them matt black will end up cooking the electronics by solar heating.
The LSST software stack has an implementation in Python. I installed the stack a couple of weeks ago — a not entirely trivial exercise but that’s another story. The learning curve is going to be a hard climb. The tutorial is good but limited.
There a number of ways. A common way is to estimate the background noise at each pixel after defect, dark and flat processing. A (relatively) simple way is to tile the image with a number of sub-images, (say 64×64 pixels by way of example) and compute the pixel histogram of each tile. Assuming that the majority of the pixels are sky and a minority are stars, discard the top 10% or so (which are presumably the stars) and fit a Gaussian to what remains (presumably the background). That Gaussian determines the sigma of the background at that point. Then interpolate (by whatever means, by a biquadratic fit, perhaps, or with cubic splines) to estimate the sigma at each pixel. The weight map is then 1/(sigma^2).
(Typo alert: undersampled to be precise…)
See also https://en.wikipedia.org/wiki/Drizzle_(image_processing)
“Drizzle has the advantage of being able to handle images with essentially arbitrary shifts, rotations, and geometric distortion and, when given input images with proper associated weight maps, creates an optimal statistically summed image.” and “Results using the DRIZZLE command can be spectacular with amateur instruments.”
Richard Hook and I were at Oxford together. He recently retired from ESO and we’re in frequent email contact.
A quick searcn turns up one for which I only have the abstract as the full text is behind a paywall.
Optimal Addition of Images for Detection and Photometry, Authors: Fischer, P ; Kochanski, G P, In: Astron. J. 107 (1994) 802-810
Abstract:
In this paper we describe weighting techniques used for the optimal coaddition of CCD frames with differing characteristics. Optimal means maximum signal-to-noise (s/n) for stellar objects. We derive formulae for four applications: 1) object detection via matched filter, 2) object detection identical to DAOFIND, 3) aperture photometry, and 4) ALLSTAR profile-fitting photometry. We have included examples involving 21 frames for which either the sky brightness or image resolution varied by a factor of three. The gains in s/n were modest for most of the examples, except for DAOFIND detection with varying image resolution which exhibited a substantial s/n increase. Even though the only consideration was maximizing s/n, the image resolution was seen to improve for most of the variable resolution examples. Also discussed are empirical fits for the weighting and the availability of the program, WEIGHT, used to generate the weighting for the individual frames. Finally, we include appendices describing the effects of clipping algorithms and a scheme for star/galaxy and cosmic ray/star discrimination.
Two much more recent papers I have read in full are https://arxiv.org/pdf/1512.06872.pdf and its sequel https://arxiv.org/abs/1512.06879 which specifically treat optimal co-addition.
Sigma clipping destroys photometric accuracy. If all I want is a pretty picture I tend to use median stacking but for scientifically useful images that’s only an option for astrometry.
I use 30s subs, so bad images can be discarded with out losing too much data, but need to use arithmetic mean co-addition for the great majority of my work.
They will be illuminated for up to 2 hours after sunset and before dawn. That’s all night at these latitudes at this time of year. Over on Twitter there is a great deal of discussion which includes amateur and professional astronomers.
https://twitter.com/doug_ellison/status/1132443682018226176 is a good place to start.
One person points out that when in a few years time the whole 12,000 constellation is in orbit, SST will be on stream and observing much of the sky every night. Even if spread out as far as possible there will be one Starlink satellite every 3.4 square degrees. The field of view of LSST is 9.3 square degrees. (Apologies for having 1.5 in the first version of this post).
It’s going to be a nightmare.
Yes, you should take frequent flats if you wish to do photometry at the highest precision possible. The out of focus dust ring-images change in size and intensity as the focus changes.
Most everyone, myself included, ignore this effect and use a set of flats for lengthy periods.
A quick kick of the tyres left me impressed but there is something I spotted. Is the longitude positive going east or west? For instance, La Palma is roughly 17W. Is that longitude 17 or 343?
Tracie, I understand your concerns but my teenage observations were made from light-polluted suburban Derbyshire, not a dark site. Today, despite my aging eyes, I still have no difficulty at all observing it from home 10km due south of brilliantly lit Cambridge (the VS is circumpolar …) and in a garden lit by neighbours.
I do not know where Tracey’s members live in North Wales but I remember the skies being markedly darker (and cloudier) there than they were in Derbyshire and my guess is that they are likely darker than where I now live.
Much the same with me, but the other way round. TheSkyX is installed but, strangely perhaps, prefer The Sky 6. MaximDL 6 is used for camera control, including guiding. My experience is that it guides very well as long as there is a bright enough star within the field of the SBIG-8 / AO-7 AG combination.
For VS work I tend to take enough 30s subs to achieve an acceptable SNR and then move on to the next target. MaxIm DL’s stacking function is invaluable for this. Given that some variables can change by several magnitudes from night to night, my approach can save significant telescope time. To avoid confusion: Maxim DL is used only as a first-look eyeballing procedure, not for final analysis where a local installation of astrometry.net and SWarp is used for stacking.
Naked eye observations of delta Cephei introduces people to variable star observing. This particular star has the benefit of being bright (visible in light polluted areas), good comparison stars nearby, circumpolar (it doesn’t matter what time of year it is and so suitable for long-term observation) and varies markedly over a short time scale (conducive to making it interesting to beginners).
Pooling the results of several of your members will help bring out the variations more clearly and phase-folding observations made over a period of weeks or months should show the nice sawtooth light curve of a classical Cepheid.
Somewhere I still have the observations I made as a young teenager. It’s how I became interested in observing variables.
