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Astrosat: forecasting satellite transits for optical astronomical observations

Osborn, James; Blacketer, Laurence; Townson, Matthew J; Farley, Ollie JD

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Laurence Blacketer

Ollie JD Farley


The impact of large-scale constellations of satellites, is a concern for ground-based astronomers. In recent years there has been a significant increase in the number of satellites in low-Earth orbit and this trend is set to continue. The large number of satellites increases the probability that one will enter the field of view of a ground-based telescope at the right solar angle to appear bright enough that it can corrupt delicate measurements. We present a new tool ‘Astrosat’ that will project satellite orbits onto the RA/Dec. coordinate system for a given observer location and time and field of view. This enables observers to mitigate the effects of satellite trails through their images by either avoiding the intersection, post-processing using the information as a prior or shuttering the observation for the duration of the transit. We also provide some analysis on the apparent brightness of the largest of the constellations, Starlink, as seen by a typical observatory and as seen with the naked eye. We show that a naked eye observer can typically expect to see a maximum of 5 Starlink satellites at astronomical twilight, when the sky is dark. With the intended 40 000 satellites in the constellation that number would increase to 30.


Osborn, J., Blacketer, L., Townson, M. J., & Farley, O. J. (2022). Astrosat: forecasting satellite transits for optical astronomical observations. Monthly Notices of the Royal Astronomical Society, 509(2), 1848-1852.

Journal Article Type Article
Acceptance Date Oct 14, 2021
Online Publication Date Oct 20, 2021
Publication Date 2022-01
Deposit Date Nov 22, 2021
Publicly Available Date Feb 1, 2022
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 509
Issue 2
Pages 1848-1852


Published Journal Article (927 Kb)

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Copyright Statement
© 2021 The Author(s) Published by Oxford University Press on behalf of The Royal Astronomical Society.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.

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