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Not an actual astronomer, but somewhat aware of detector issues for space-based telescopes. Typically, you want to use one single integration time, if possible

Not an actual astronomer, but somewhat aware of detector issues for space-based telescopes. Typically, you want to use one single integration time, if possible. Doing so can limit readout noise, for one thing. (Note that ground-based astrophotographers, with consumer cameras, often take multiple exposures to cool down the detectors. This is not a factor with the actively-cooled detectors in astronomical telescopes.) For instance, the observations leading to the recent discovery of the two-planet exosystem [1] used roughly 15-minute integration times [2, sec. 2] across an 8 meter (!) aperture. This is a longer integration time than the 17, 30-second integrations that produced OP. I think the above considerations about stacking vs single exposures are a side issue, though. The saving grace is that many astronomical observations are narrow-field-of-view, and are done away from the illuminated part of the StarLink constellation. But, surveys or wide-field images could really be affected strongly, at the 30-40% level [3]. [1] https://news.ycombinator.com/item?id=23917559 https://news.ycombinator.com/item?id=23917559 [2] https://academic.oup.com/mnras/article/492/1/431/5680498 https://academic.oup.com/mnras/article/492/1/431/5680498 [3] https://www.eso.org/public/archives/releases/sciencepapers/eso2004/eso2004a.pdf https://www.eso.org/public/archives/releases/sciencepapers/e...

rimliu 6y ago
There are plenty of amateurs using actively cooled specialized astrophotography cameras with total integration times reaching hours (2-3 are typical). Readout noise can be cancelled by taking so called bias frames. Shorter exposures are sometimes preferable because of the light pollution and to minimize the possibility of an exposure being rendered usles by some plane or satellite: it is less painful to throw away three minutes of exposure time than 15.
- mturmon 6y ago
  > Readout noise can be cancelled by taking so called bias frames. That’s not what bias frames [1] are doing. Bias frames measure a systematic effect in the conversion of stored charge to a digital number in the CCD device. You can then subtract it out. The calibration offered by bias frames does not fix readout noise, which is a random, not systematic, effect that is inherent in the same conversion. You can use the bias frames to compute the strength of the readout noise (i.e., the rms magnitude of its random part) but you can’t remove the random noise itself. See sec. 1.1 of the linked reference for more. [1] https://users.astro.ufl.edu/~lee/ast325/handouts/ccd.pdf https://users.astro.ufl.edu/~lee/ast325/handouts/ccd.pdf
  - rimliu 6y ago
    The point of bias frames is what you take them without accumulating any charge. Well yes, you cannot eliminate random noise, but you can reduce it. Also, most popular deidcated astrophotography cameras are now CMOS not CCD and readout differs in these. Your link does not work, and probably for the better. See this instead: https://www.youtube.com/watch?v=O6oGyFlZgAc https://www.youtube.com/watch?v=O6oGyFlZgAc

rimliu 6y ago

There are plenty of amateurs using actively cooled specialized astrophotography cameras with total integration times reaching hours (2-3 are typical). Readout noise can be cancelled by taking so called bias frames. Shorter exposures are sometimes preferable because of the light pollution and to minimize the possibility of an exposure being rendered usles by some plane or satellite: it is less painful to throw away three minutes of exposure time than 15.

mturmon 6y ago
> Readout noise can be cancelled by taking so called bias frames. That’s not what bias frames [1] are doing. Bias frames measure a systematic effect in the conversion of stored charge to a digital number in the CCD device. You can then subtract it out. The calibration offered by bias frames does not fix readout noise, which is a random, not systematic, effect that is inherent in the same conversion. You can use the bias frames to compute the strength of the readout noise (i.e., the rms magnitude of its random part) but you can’t remove the random noise itself. See sec. 1.1 of the linked reference for more. [1] https://users.astro.ufl.edu/~lee/ast325/handouts/ccd.pdf https://users.astro.ufl.edu/~lee/ast325/handouts/ccd.pdf
- rimliu 6y ago
  The point of bias frames is what you take them without accumulating any charge. Well yes, you cannot eliminate random noise, but you can reduce it. Also, most popular deidcated astrophotography cameras are now CMOS not CCD and readout differs in these. Your link does not work, and probably for the better. See this instead: https://www.youtube.com/watch?v=O6oGyFlZgAc https://www.youtube.com/watch?v=O6oGyFlZgAc