What is Satellite flare?

Satellite flare, also known as satellite glint, is a satellite pass visible to the naked eye as a brief, bright "flare". It is caused by the reflection toward the Earth below of sunlight incident on satellite surfaces such as solar panels and antennas. Streaks from satellite flare are a form of light pollution that can negatively impact ground-based astronomy, stargazing, and indigenous people.

Many satellites flare with magnitudes bright enough to see with the unaided eye, i.e. brighter than magnitude +6.5. Smaller magnitude numbers are brighter, so negative magnitudes are brighter than positive magnitudes, see apparent magnitude.

The Iridium constellation was one of the first anthropogenic sources of near-space light pollution to draw criticism. Larger satellite constellations, like OneWeb and Starlink, have received increased criticism. Scientific and policy analyses have raised questions about which regulatory bodies hold jurisdiction over human actions that obscure starlight in ways that impact astronomy, stargazers, and indigenous communities.