Motorola have recently placed a
collection of nearly 70 Satellites in Orbit approx. 780km above
the Earth. Their purpose is for the Motorola Iridium mobile phone
system that allows you to use your Iridium mobile phone anywhere
on the planet. However, there is an interesting phenomenon that
occurs at certain times during their orbit.
At certain times when the
Sun-Satellite-Observer angle is just right, their highly
reflective Main Mission Antenna (MMA), which are about 188cm x
86cm in size, will cause a brilliant flare for about 5 to 20
seconds. These normally very faint satellites can often briefly
outshine all of the other night sky objects (up to -8 magnutude)
and can even be see during the day if you are on or near the
north-south line of maximum reflection.
The flares usually occur
during the twilight hours before and after sunrise and always
follow a north-south line. This gives you a hint of where to
look. In Australia they always look best when they are in the
southern sky as they wrap around under the South Pole. No
telescope or binoculars are needed to see these little beauties.
All you need is a reliable prediction source so you know when and
where to look. See below if you are interested.
To find the Iridium Flares you need a reliable prediction source such as the GSOC Satellite Predictions Homepage however first of all you need to find out where your position on earth is. The GSOC page does have latitudes and longitudes for most major cities around the world however to get the most accurate predictions you need to give accurate co-ordinates. (Anyone got a GPS?) If you don't have a GPS and you live in Australia a convenient place to find this info is at Australian Geographic Names and Places web site. You can search for your town by name. As well as displaying details for towns it displays details for parks, railway stations, bridges, creeks, rivers etc which will give you an even more accurate location if you live near a park or a railway station. The output is also presented in decimal degrees, which is the format required by GSOC. Once you have obtained your location details, go to the GSOC web site, follow the instructions then Bookmark the Main Page so next time you go back you don't have to enter all the co-ordinates over again.
The GSOC Satellite Visibility Home page generates Iridium Flare predictions for next 7 days. As well as giving time, altitude and direction to look, it also gives a predicted brightness for your location. It also lists how far (east or west) off the central line you are, and the magnitude expected on the central line (just in case you want to go for a drive to see it better). If you are within about 10km of the Flare center there will be little noticeable dimming.
The GSOC page also gives predictions for the Russian Space Station (MIR) and the International Space Station (ISS). Both MIR and ISS are the brightest satellites because they are large objects and are in a relatively low orbit at approx. 400km. The site also gives Daily predictions for ALL satellites brighter than Magnitude 4.5 (which is the dimmest the naked eye can see). There are also some other neat features like daily Sun & Moon rise and set times, ISS & MIR orbit simulations etc. It really is well worth a look.
OK so to recap,
Magnitude is a measure of brightness used by Astronomers. The Greeks, who classified the stars as first magnitude (brightest) to sixth magnitude (dimmest), devised this method originally. This rough method was altered in the 1800's so that magnitude (mag.) 1 stars were defined as being exactly 100 times bright than mag. 6 stars.
Thus at one extreme the Sun is magnitude (mag.) -27 and some of the faintest observed stars around mag. +24. The full moon is mag. -12.5, Sirius the brightest star in the night sky mag. -1.5, whilst the faintest stars visible to the naked eye under good conditions are around mag. +6.
Iridium Flares can be as bright as mag. -8 while MIR and the ISS can be as bright as mag. -1 if the conditions are right.
For more information about Iridium Flares and Satellite observing in general you should check out the Visual Satellite Observer's Home Page this page is an excellent source of information.
Copyright ©1999 - Warren Leadbeatter
Last Updated - 16 May, 1999
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