Earlier this month, SpaceX successfully launched the first set in a new generation of communication satellites—and signaled the end of a popular sky-watching phenomenon.

Known as Iridium flares, the brief but dramatically bright flashes are predictable night sky events easily seen with the naked eye, even under heavily light-polluted city skies. The flares are caused by sunlight bouncing off Iridium communication satellites, a constellation of 72 probes launched between 1997 and 2002.

The new Iridium satellites are designed to replace this aging network and offer a much needed upgrade to global satellite telephone capabilities. But the latest models will not produce the same impressive flares, which means the sky show will cease when the updated network is complete in 2018.

Brilliant Burst

Backyard sky-watchers have been enjoying Iridium flares since the first launch. The flares are a brilliant product of three large silver-coated antennae perched on each satellite.

For a few seconds at a time, sunlight glints off these mirror-like panels in just the right way that the satellite appears as a dazzling point of light anywhere from 5 to 20 seconds at a time. The star-like point normally shines just at the threshold of human vision from a dark sky.

But at the right angle, these flares can surge in brightness. For a few seconds, they can outshine nearly anything else in the night sky, even the International Space Station and Venus, the brightest planet visible to the unaided eye. These fleeting flares can be so bright that you can even spot them during the day if you know exactly where and when to look.

Some of the first-generation satellites have gone offline and are tumbling in orbit. Their flares can be especially short, lasting only a quarter-second.

Not surprisingly, sky-watchers are sometimes surprised by Iridium flares and will report seeing an ordinary star mysteriously undergo a sudden surge in brightness, as if that star had exploded as a supernova.

But satellite tracking websites can help you hunt Iridium flares and double-check any unexpected flashes—at least for a few more months.

Days Numbered

The satellite changeout began on January 14, with the successful liftoff of a SpaceX Falcon 9 rocket from Vandenberg Air Force Base in California. That rocket delivered a cluster of ten probes to low-Earth orbit, the first in the Iridium NEXT satellite network. Over the next 18 months, rockets will send up a total of 81 new Iridium satellites.

View Images A SpaceX Falcon 9 rocket lifted off from California carrying Iridium NEXT satellites on January 14. Photograph by SpaceX, Alamy Stock Photo

Once activated, the new satellites will offer state-of-the-art broadband services and provide real-time global aircraft surveillance capabilities. Unfortunately for sky-watchers, they are also smaller and have different antenna designs, making them significantly less reflective.

Once each new spacecraft's health checks out, the older satellites will be decommissioned and sent to a fiery death in Earth’s atmosphere, bringing an end to Iridium flares.

Now is definitely the time to spot these celestial flashes for yourself before they wink out for good. The first step is to figure out your precise geographic location, because each potential flare has a relatively narrow viewing path on Earth, usually no more than 31 miles wide.

Many satellite tracking websites offer customized visibility tables for the flares, which will give you the specific timing and direction information for each event over many days in your specific locale. Then it’s as simple as going outside and looking up.

So on the next clear night, try your luck at hunting down an eye-catching Iridium flare before they disappear for good.