Satellite shadows through stellar occultations

Abstract

Aims. The impact of mega-constellations of satellites in low-Earth orbit during nighttime optical observations is assessed. Methods. Orbital geometry is used to calculate the impact of stellar occultations by satellites on the photometry of individual stars as well as the effect on the photometric calibration of wide-field observations. Results. Starlink-type satellites will have occultation disks several arcseconds across. Together with occultation crossing times of 0.1−100 ms, this will lead to photometric ‘jitter’ on the flux determination of stars. The level of impact for a given star depends on the ratio of the integration time of the frame over the occultation crossing time. In current-day CCD-based synoptic surveys, this impact is negligible (≪1%), but with future CMOS-based wide-field surveys obtaining data at frequencies >1 Hz, the impact will grow towards complete dropouts. At integration times similar to the occultation crossing time, the orbit of a satellite can be traced using the occultation method. At even shorter integration times, the shape of the occulting satellite can be deduced. Conclusions. Stellar occultations by passing satellites, enabled by high-speed CMOS technology, will be a new method for studying orbiting satellites. Large-scale monitoring programs will be needed to independently determine and update the orbits of satellites.