Irridium satellites will give a real buzz the first time you see one. If they don't, then class yourself as a steely eyed missile person :-)

Iridiums are a part of a 60 or so constellation of low earth orbiting satellites that provide cellular like mobile phone communications from any position on the planet that can see the sky.

Whilst not normally so visible under normal conditions, these satellite each carry three large highly reflective antennas (MMA's, main mission antennas) aranged at 120 degree spacing around the body of the spacecraft and inclined down towards the earth. In order to provide the coverage they do, Iridium satellites are maintained in a precise attitude as they orbit the earth. This precise attitude allows calculations to be made that will determine within a few km or so on the Earth's surface when the Sun will glint off the MMA's and be visible at your location. The thing that makes Iridiums interesting is that whilst most other satellites will be visible as a steady moving dot across the sky, the Iridium's precise orbital attitude causes them to be visible only for a short time, as the MMA lines up with the Sun and you, and then moves on along it's orbit. Typical flares as they're known last 10 - 15 seconds, and to the untrained eye are invisible at all other times. As you get used to watching for them you'll see them for a short while before and after the flare as dim fast moving objects.

What will you see? When everything is right, you'll see the brightest thing in the sky apart from the sun and the Moon (and maybe that bloomin' street light!). At their brightest, Iridium satellite flares can reach magnitude minus 9. At other times, you'll see Iridium flares at magnitudes down to zero. Due to the polar orbit of Iridium satellites, you've more chance of seeing Iridium flares at higher northern lattitudes and lower southern lattitudes. Folks near the equator need a little more patience (and we do have it don't we!)

The easiest way to check out Irridium flares is to visit the Heavens Above website and registering your co-ordinates. While our link on the left provides general satellite info at HA, it would be impossible to give links here for Iridiums as a difference in longtitude of a couple of Km could give a result differing by at least an order or two of magnitude, possibly miss a good pass and generally give erroneous results. Once you've registered on HA you also get customised access to loads of other Good Stuff(TM).

Other satobs software? There's loads of it - do a google for satellite observation software. There are many diffrent packages to choose from. Once you have the software, you'll need to feed it with some satellite data. This data is known as Two Line Elements, or TLE's, or Elsets. You can download current elements from from various sources, including Celestrak and your very own Tropical Stargazers website, which maintains a daily compilation of the most interesting and brightest satellites on our Satellite Elsets page.

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