Forum Replies Created
-
Posts
-
Detection of Rotational Variability in Floofy Objects at Optical Wavelength https://arxiv.org/abs/2103.16636
The first Dobsonian I had showed serious spherical aberration.
Worked just fine as a light bucket, which I what I wanted it for.
Yes!
Please try it if you can; you only have a few more days of it being bright enough.
Really regretting not being in La Palma right now.
Further: note that the proposed rotation period of only 25 seconds implies that exposures of only a few seconds will be needed to get a good light curve. In practice, this suggests only 0.7m-class or larger telescopes will be able to do this successfully, likely implying the use of robotic telescopes.
Getting colour indices, on the other hand, should be somewhat easier as exposures >25s will average out the rotational behaviour. This could be a productive use of personal telescopes fitted with two or more standard photometric filters.
My thanks to Richard Miles and Tomasz Kwiatkowski for the further information.
And vice versa, in my experience. Over-long USB cables can give connection problems which are sometimes solved by using a powered hub.
Try it both ways, in other words.
I have absolutely no idea whether this might be an explanation, but I believe that aurorae produce radio waves which can be picked up by radio receivers.
There have been documented cases of unexpected diodes (akin to the good old cat’s whisker) producing audio outputs from AM radio transmissions. A few cases involved mercury amalgam dental fillings, for example.
I wonder whether this may be relevant.
You could always just suck it and see. It shouldn’t take more than one night to take dozens of exposures of a relatively bright star at a variety of settings. Then process them and see what works best for your equipment.
You make a good point, but up here in the sub-arctic the night time is very often at or below fridge temperature (~5C). When it doesn’t it often never gets dark at night anyway.
At the opposite extreme, a good calima in La Palma can result in the air temperature being higher than 20C all night and even a good two-stage Peltier cooler can’t get a camera much below -15C. Been there, done that.
I have an Odroid running Ubuntu and Kstars/EKOS as a proposed replacement TCS. I have been quite unable to find a driver for the dome controller (a Vellman board) and there are still teething problems with the mount (a FS2 controller). All the SX kit works perfectly; not yet tried the focuser. It will be months before I can return to La Palma and try to resolve these issues. 8-(
A Celestron NEXIMAGE 5 purchased via the BAA forum also fails to work under the local Ubuntu installation but I have found a package which claims to contain a driver for the camera.
Other people with more main-stream equipment have no significant problems with Linux-based controllers.
I whole-heartedly agree!
As already stated, I also generally run in 2×2 binning mode for photometry.
My Lodestar 2 works very nicely. Whether it has an abnormally large (or small, for that matter) I couldn’t say.
I think what we are really saying is that you have to pay attention!
Astrometry could well be different from photometry which could well be different from spectroscopy which could well be different from bare detection which could well be …
To summarize: think about what you wish to achieve and make your decisions in that light.
Robin, thank you very much for posting the link to http://spiff.rit.edu/richmond/signal.shtml which I had not seen before and have now bookmarked.
Typing in the values for my set-up confirmed my prejudice that the read noise is almost entire unimportant for the photometric work I do, where I generally take 30s to 60s subs and co-add.
Note with CCD cameras (not CMOS), in camera binning (as opposed to post binning) reduces the read noise as there is only one dose per binned super-pixel
That is true, but the read noise adds in quadrature whereas the signal adds. The post-binning signal to noise ratio per NxN binned pixel is N times that of the unbinned pixels.
That is why I was careful to state that the dynamic range can be improved by a factor of NxN for N-fold post-binning, and not the signal to noise ratio. Sometimes the dynamic range is particularly important, such as when trying to detect extremely low contrast objects for instance.
FWIW, I generally use in-camera binning for photometry and post-binning for simple detection. The reason for the former is primarily for faster download times and smaller image sizes, rather than any read noise consideration. Read and dark noise is so small on my cooled CCD camera that it is completely overwhelmed by photon noise from the object and the sky. It is way down in the noise, to coin a phrase 😉
Entirely agree about the under/over confusion but failed to mention it earlier. I am pleased that you have done so.
You can always do post hoc binning. What you can not do is undo any binning already applied.
In particular, performing NxN binning in software afterwards gives you the opportunity to increase your dynamic range N^2 -fold by either summation if you can avoid integer overflow or averaging to a floating point format if you can’t — the two are equivalent from a signal processing point of view.
Ah, that may explain the final “2” character. It is presumably there to avoid confusion for modern readers.
An ancient writer would have written 9000 as 2-30 (i.e. 2*60+30 = 150) with the final multiplication by 60 being implied. Their mathematicians did have a character for zero but it was only ever used in intermediate positions and never to set the scale. So 9000, 150, 5/2 and 1/24 would all be written 2-30.
(Added in edit)
Incidentally, those of us old enough to know how to use a guessing stick (“slipstick” on the other side of the pond) rarely had any problem with a lack of leading or trailing zeros. The Mesopotamian scribes very occasionally got it wrong, but I doubt that they did so more often than we did.
The human lifespan is pitifully short at present. If our life expectancy was, say, a million years a journey which took ten thousand years would only be 1% of our life. At present, 1% of a human lifespan corresponds to 9 months or so. Many people have embarked on journeys with that amount of travel time.
It might be easier to take the slow (100km/s) approach than the fast (200,000km/s) if medical technology progresses faster than its transportation equivalent.
