This interesting answer to What is the LSST's plan to address frequent satellite trails in data? quotes:

From the LSST webpage:

The first group of Starlink satellites are sufficiently bright during dawn and dusk (when LSST would be surveying) that the trail would exceed sensor saturation, generating uncorrectable artifacts in the data. If instead these satellites were painted flat black making them a factor of 25 fainter, satellite trails should be less of a challenge for LSST due to its specific design.In that case LSST's frequent imaging of the same region of sky will provide enough data to correct for unsaturated satellite trails or other anomalies.

But now I'm wondering about something a little different. How do large telescopes doing surveys avoid saturation-induced artifacts caused by the brightest stars and planets? Their positions are of course absolutely predictable, so I suppose it's possible to keep their images slightly off of the silicon, and "walk around" them with a series of exposures, is that what the LSST will do?

There are other possibilities, for example a small, mechanical obscuring disk that can be introduced ahead of the CCD to cast a small slightly diffuse shadow, or in the case of multiple CCDs one could put the object between two sensors.

Question: If this is this done in practice, how? Is the LSST planned to have a way to avoid this problem?


1 Answer 1


Large surveys don't usually bother to do anything about bright stars saturating the images. It is more trouble than it is worth to deal with, and these kinds of surveys are designed to study much fainter things. The data from bright stars are just unusable. If an astronomer really wants data on a bright star, they can go to a smaller telescope and/or take their own observations with filters/apertures to reduce the light from the star going through the optics.

Here you can see one of the many examples of bright stars saturating the detectors on the SDSS survey: http://skyserver.sdss.org/dr15/en/tools/chart/navi.aspx?ra=81.5049695271329&dec=-5.52153697792986

enter image description here

  • $\begingroup$ Thanks for your answer! The reason I asked "especially" about LSST is it's high imaging cadence, large field, and that it will produce about 10 million alerts per night so the automatic alert generating system may trigger on artifacts like blooming. So in this case I think that if they don't avoid saturation by rapid successive readouts or a mechanical occulter, they'll at least have a systematic way to avoid saturation artifacts in analysis. $\endgroup$
    – uhoh
    Commented Nov 15, 2019 at 1:02

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