A revolutionary system of man-made Earth satellites launched by Motorola to provide a planet-wide communication system. Seventy seven satellites were originally planned for launch, the name for the  system or constellation, iridium, was coined after the 77th element of the periodic table. The extremely high cost of construction, launch and maintenance of the constellation, together with an over-optimistic expectation of return-on-investment forced the company to file for bankruptcy. Without maintenance the investment was doomed as the satellite's orbits needed continual boosting to prevent eventual burn-up upon re-entry into the atmosphere. After much discussion and intense bargaining a financing plan put forward by a group of investors was accepted and the company is now known as Iridium Satellite LLC.

The system has been the cause of a long-running controversy as it has added significantly to the number of satellites orbiting the Earth with predictable impact on the work of ground-based observers. During each orbit sunlight reflects off the highly polished satellite surfaces causing a cone of reflected sunlight to sweep over the Earth. At night, a suitably positioned observer will see the satellite initially as a faint "moving star" that grows rapidly in brightness and then fades away, as the cone of light passes across the observer's eyes. These are known as "Iridium flares" and can be as bright as a dazzling magnitude -8!

Below are some images of Iridium flares that have been captured over the past few years.


Iridium 45 (mag -7) imaged from Elwood Beach,  Australia, on the 29th October 2004.

iridium1vsm.jpg (3345 bytes)

A mag -8 flare that was imaged at 20:25 UT on the 16 March 2001 as it appeared against the stars of Ursa Major; 20 sec exposure onto 400ASA film through a 28mm lens at f/1.8.

iridium2vsm.jpg (4320 bytes)

An accidental iridium flare image! I was photographing the Aquila region and  skywatching when I caught a bright glint out of the corner of my eye. When the film was developed I was delighted to find what I thought to be a fireball, but the trail was just too symmetrical to be a meteor! 5 min exposure onto Kodachrome 200 slide film through a 28mm lens at f/1.8.

Iridium 95 captured at 23:28UT on the 1st July 2003; mag -7.

Iridium 57 captured at 22:24UT on the 25th July 2003; mag -7. Arcturus is the bright star at top left of the flag pole.


Sky Home