Since 2019, SpaceX has been launching an increasing number of internet satellites into orbit around Earth. The satellite constellation, called Starlink, now includes nearly 1,800 members orbiting at altitudes of about 550 kilometers. Astronomers have expressed concerns that that these objects, which can appear as streaks in telescope images, could hamper their scientific observations.

To quantify these effects, a team of researchers studied archival images captured by the National Science Foundation (NSF)-funded Zwicky Transient Facility (ZTF), an instrument that operates from Caltech's Palomar Observatory near San Diego. ZTF scans the entire night sky every two days, cataloging cosmic objects that explode, blink, or otherwise change over time. This includes everything from supernovae to near-Earth asteroids. The Zwicky team members say they decided to specifically study the effects of Starlink satellites because they currently represent the largest low-Earth orbit, or LEO, constellation, and they have well-characterized orbits.

The findings, reported in the January 17 issue of The Astrophysical Journal Letters, shows 5,301 satellite streaks appear in archival images taken between November 2019 and September 2021. The streaks are most apparent in so-called twilight observations, those taken at dawn or dusk, which are important for finding near-Earth asteroids that appear close to the sun in the sky.