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First observations and magnitude measurement of Starlink’s Darksat

Tregloan-Reed, J. and Otarola, A. and Ortiz, E. and Molina, V. and Anais, J. and González, R. and Colque, J. P. and Unda-Sanzana, E. (2020) First observations and magnitude measurement of Starlink’s Darksat. Astronomy and Astrophysics, 637 . Art. No. L1. ISSN 0004-6361. doi:10.1051/0004-6361/202037958.

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Aims. We measured the Sloan g′ magnitudes of the Starlink’s STARLINK-1130 (Darksat) and 1113 low Earth orbit (LEO) communication satellites to determine the effectiveness of the Darksat darkening treatment at 475.4 nm. Methods. Two observations of the Starlink’s Darksat LEO communication satellite were conducted on 2020/02/08 and 2020/03/06 using Sloan r′ and g′ filters, respectively. A second satellite, STARLINK-1113, was observed on 2020/03/06 using a Sloan g′ filter. The initial observation on 2020/02/08 was a test observation conducted when Darksat was still in the process of manoeuvring to its nominal orbit and orientation. Based on the successful test observation, the first main observation took place on 2020/03/06, along with an observation of the second Starlink satellite. Results. The calibration, image processing, and analysis of the Darksat Sloan g′ image gives an estimated Sloan g′ magnitude of 7.46 ± 0.04 at a range of 976.50 km. For STARLINK-1113, an estimated Sloan g′ magnitude of 6.59 ± 0.05 at a range of 941.62 km was found. When scaled to a range of 550 km and corrected for the solar and observer phase angles, a reduction by a factor of two is seen in the reflected solar flux between Darksat and STARLINK-1113. Conclusions. The data and results presented in this work demonstrate that the special darkening coating used by Starlink for Darksat has darkened the Sloan g’ magnitude by 0.77 ± 0.05 mag when the range is equal to a nominal orbital height (550 km). This result will serve members of the astronomical community who are actively modelling the satellite mega-constellations to ascertain their actual impact on both amateur and professional astronomical observations. Both concurrent and subsequent observations are planned to cover the full optical and NIR spectrum using an ensemble of instruments, telescopes, and observatories.

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Additional Information:© ESO 2020. Received 13 March 2020 / Accepted 15 April 2020. We would like to thank the two referees, Dr. Gregg Wade and Dr. Olivier Hainaut, for their helpful comments which improved the quality of this work. This work was supported by a CONICYT / FONDECYT Postdoctoral research grant, project number: 3180071. JTR thanks the Centro de Astronomía (CITEVA), Universidad de Antofagasta for hosting the CONICYT / FONDECYT 2018 Postdoctoral research grant. EU kindly acknowledges the work of Marco Rocchetto and Stephen Fossey to set up Ckoirama. We are grateful to both Dr. Patrick Seitzer and Dr. Tony Tyson for useful comments on the manuscript and their encouragement. We extend a special thanks to Boris Haeussler, Felipe Gaete, Steffen Mieske, Stéphane Brilliant, Joseph Anderson, ESO Paranal, for observations which will be included in a follow-up manuscript. The following internet-based resources were used in the research for this paper: the NASA Astrophysics Data System; the ESO Online Digitized Sky Survey, the SIMBAD database and VizieR catalogue access tool operated at CDS, Strasbourg, France; and the arχiv scientific paper preprint service operated by Cornell University.
Group:Thirty Meter Telescope
Funding AgencyGrant Number
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)3180071
Subject Keywords:techniques: photometric / light pollution / methods: observational
Record Number:CaltechAUTHORS:20200430-151240298
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Official Citation:First observations and magnitude measurement of Starlink’s Darksat J. Tregloan-Reed, A. Otarola, E. Ortiz, V. Molina, J. Anais, R. González, J. P. Colque and E. Unda-Sanzana A&A, 637 (2020) L1 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:102944
Deposited By: George Porter
Deposited On:01 May 2020 14:28
Last Modified:16 Nov 2021 18:16

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