For nearly two decades, Iridium flares were among the most spectacular predictable events in the night sky. A brief, brilliant flash of light — sometimes reaching magnitude –8, far brighter than Venus — that lasted only a few seconds before fading away. For those who knew when and where to look, it was an unforgettable sight.
What Caused Iridium Flares?
The original Iridium communications constellation consisted of 66 operational satellites (plus spares) launched between 1997 and 2002. Each satellite had three highly reflective, door-sized aluminium antenna panels angled at 40° from the satellite body.
When sunlight hit one of these polished panels at just the right angle, it acted as a mirror — reflecting a concentrated beam of sunlight towards the ground. If you happened to be standing in the path of that reflected beam (typically only a few kilometres wide), you would see an intensely bright flash lasting 5–20 seconds.
Because the satellites followed predictable orbits and their antenna geometry was precisely known, flares could be predicted with remarkable accuracy — to the second and to the degree of sky position.
How Bright Were They?
At magnitude –8, an Iridium flare was bright enough to be seen in twilight and even caught the attention of people who were not looking for it. The flash was so bright it could cast faint shadows.
Can You Still See Iridium Flares?
The original Iridium constellation has been almost entirely replaced by Iridium NEXT satellites, which were specifically designed without the large reflective antenna panels that caused the flares. The deorbiting of the original satellites, which took place primarily between 2017 and 2019, brought an end to the era of reliable, predictable Iridium flares.
A small number of original Iridium satellites may still be in orbit as debris, and these can occasionally produce unexpected glints. However, these are sporadic and unpredictable — the days of reliable Iridium flare predictions are over.
The Legacy
Iridium flares played a significant role in making satellite watching a popular hobby. Websites and apps that predicted flares introduced millions of people to the idea that satellites could be observed from the ground, paving the way for the current era of ISS and Starlink spotting.
For satellite photographers, Iridium flares were especially prized — a brilliant point of light that could be captured with precise timing, creating dramatic images of a single bright flash among the stars.