Simultaneous Multicolor Observations of Starlink's Darksat by The Murikabushi Telescope with $MITSuME$

TL;DR

This study uses multicolor observations to compare the brightness and surface properties of Starlink satellites, revealing differences in reflectance and albedo, with implications for understanding satellite visibility and darkening treatments.

Contribution

First simultaneous multicolor observations of Starlink satellites, providing new insights into their brightness, color, and surface reflectance properties.

Findings

Darksat's brightness is comparable or brighter than STARLINK-1113.

Reflected flux of STARLINK-1113 is significantly redder than Darksat.

Darksat's albedo is about half that of STARLINK-1113.

Abstract

We present the $g'$-, $R_{\rm c}$-, and $I_{\rm c}$-band magnitudes and associated colors of the Starlink's STARLINK-1113 (one of the standard Starlink satellites) and 1130 (Darksat) with a darkening treatment to its surface. By the 105 cm Murikabushi telescope/$\it{MITSuME}$, simultaneous multicolor observations for the above satellites were conducted four times: on April 10, 2020, May 18, 2020 (for Darksat), and June 11, 2020 (for Darksat and STARLINK-1113). We found that (1) $g'$-band apparent magnitudes of Darksat ($6.95~\pm~0.11-7.65~\pm~0.11$ mag) are comparable to or brighter than that of STARLINK-1113 ($7.69~\pm~0.16$ mag), (2) the shorter the observed wavelength is, the fainter the satellite magnitudes tend to become, (3) the reflected flux by STARLINK-1113 is extremely ($> 1.0$ mag) redder than that of Darksat, (4) there is no clear correlation between the solar phase angle and orbital-altitude-scaled magnitude, (5) by flux-model fitting of the satellite trails with the blackbody radiation, it is found that the albedo of Darksat is about a half of that of STARLINK-1113. Especially, the result (1) is inconsistent with the previous studies. However, considering both solar and observer phase angles and atmospheric extinction, the brightness of STARLINK-1113 can be drastically reduced in the $g'$ and $R_{\rm c}$ band. Simultaneous multicolor-multispot observations more than three colors would give us more detailed information regarding the impact by the low Earth orbit satellite constellations.