By Tony Cook
A new batch of commercial satellites is orbiting Earth and
will impact greatly on every person who watches the sky.
What is Iridium?
Over the last few months, advertising has begun in Australia
promoting a new, global, mobile telephone service called Iridium.
Iridium consists of 66 identical operational satellites in
LEO (Low Earth Orbit). There are also satellites in orbit which
have failed and others that are spares bringing the total to
84 as of writing this article.
These satellites perform the same task as the many mobile phone
antenna towers that are springing up throughout our community
and provide mobile telephone coverage to every point on the surface
of the Earth.
The first group of satellites was launched in May, 1997 by a
Boeing Delta II rocket and regular launches have occurred since.
Some groups have been launched by Russian Proton and Chinese
Long March 2C/SD rockets.
Each satellite orbits at 780 kilometres (485 miles) above Earth
making one orbit every 100 minutes. The orbits have an inclination
of 86.4 degrees which basically means that the satellites travel
a path between the North and South poles.
An Iridium mobile phone can cost from $5,000 Australian, with
a call cost of nearly $4 per minute.
What does Iridium have to do with UFOs?
I'm glad you asked.
Each Iridium satellite is about 4 meters long and 1 meter wide.
Attached to the bottom of each satellite are 3 Main Mission Antennae
(MMA) that are highly reflective and make a constant angle with
the Earth as the satellite orbits.
Each MMA can provide a direct reflection of the Sun which is
only tens of kilometers wide at the Earth's surface. These reflections
are known as Iridium Flares and can have a brightness of up to
magnitude -8 (as much as a half lit Moon or up to 30 times brighter
than Venus at -4.9) and last for up to 20 seconds. This would
be bright enough to see by day. An observer in the centre of
the reflections path would see a very bright flare but someone
only a few kilometers either side would see a flare that was
much reduced in brightness.
An early photograph of a Flare is included in this article thanks
to Chris Dorreman in the Netherlands.
An Iridium Flare could easily be reported as a UFO sighting.
This photo was taken by Chris Dorreman on Sept
20, 1997. It is believed to be one of the earliest pictures taken
of an unpredicted magnitude -8 (estimated) flare produced by
Details: 1 minute exposure with the satellite moving from left
This image © Chris Dorreman
Happily, as each satellites' orbit is very well known along
with its orientation, the time and location of Iridium Flares
can be accurately predicted. There are software packages as well
as Internet Web sites that can predict the Flares for your location
over the next 24 hours to 7 days and also review Flares over
the past few days.
These resources will be very useful to VUFORS to enable us to
ascertain whether a reported sighting is related to an Iridium
Visual Satellite Observers Homepage:
Last Updated: January,
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P.O. Box 1043 Moorabbin Victoria, Australia 3189
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