Satellite flare
- Top: a simulated animation of a typical Iridium flare
- Bottom: Both images show a flare of an Iridium satellite. Comet Holmes can be seen in the right image, slightly above the tree branch.
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 (e.g., synthetic aperture radar). Streaks from satellite flare are a form of light pollution that can negatively affect 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, i.e. the scale is reverse logarithmic .
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 affect astronomy, stargazers, and indigenous communities.