Avoiding the Chasm

October 8, 2009

Satellite Above – I Watched it for a Little While

Filed under: Technology — Tags: , , — vextasy @ 9:24 pm

Orbitron - Satellite Tracking System

A moving light in the sky is guaranteed to catch my attention. If it is slow moving and flashing then I know that it is likely to be an aircraft. If it shoots across the sky in an instant then I know it to be a meteor or shooting star. If it is fixed then I conclude that it is a star or a planet. But what if it is none of these? What if it is bright orange and moves across the sky slowly over a period of thirty seconds or so?

I asked myself that very question recently as I watched in amazement as an object that looked to me like a distant ball of fire passed silently and slowly from north-west to south-east across the clear evening sky. My initial thoughts were that I had just seen my first fireball but I knew that to be very unlikely and, besides, I was sure that fireballs were associated with freak weather conditions and on this night everything was still.

The object, whatever it was, appeared to be some distance off and moved across the sky with a speed that I readily associated with that of orbiting satellites which I had seen many times before. But these had always been white in colour and this one was a distant flaming red.

I wondered if it would be easy to check whether any satellites had passed overhead and so turned to the Internet for a solution. I came across a number of great resources which provided more than enough information to solve the mystery.

The first was a free piece of software by Sebastian Stoff called the Orbitron Satellite Tracking System which gives graphical and tabular information about the position of satellites and their visibility at a given time and place. The Orbitron software suggested that what I may have seen was a satellite which goes by the name of Iridium 43, one of a family of about seventy such satellites that provide communication services and orbit the earth from pole to pole at a height of about 500 miles and at a speed of about 17,000 miles per hour.

The Iridium satellites made the news back in February of this year when one of them, Iridium 33, collided with a retired Russian satellite and with a combined impact speed of 26,000 miles per hours both were destroyed leaving thousands of pieces of space debris to fall back to earth over the following days. The Russian satellite had been uncontrolled since, at least, 1995 but the authorities had predicted that the two satellites should have missed each other by about half a kilometre – they were clearly wrong.

Iridium satellites are known to give rise to an interesting phenomenon – the Iridium Flare. The satellites are equipped with three highly reflective door sized antenna made of silver-coated Teflon on polished aluminium  and occasionally one of these will pick up light from the sun and reflect it down onto the earth’s surface generating an illuminated spot on the earth about 6 miles across. To an observer on the surface of the earth the satellite appears as if from nowhere as a faint object that slowly increases in brightness to a maximum and then just as quickly dims until it is no longer visible, with the whole show lasting no longer than, perhaps, thirty seconds. A simulation is shown here. The satellite that I saw appeared a rich flaming red in colour but I put that down to atmospheric conditions and its effect on the light as it was reflected from the satellite down to earth.

A really excellent web site that makes it easy to determine when and where to look out for satellites that are likely to be visible to the naked eye is Heavens Above. Start by declaring your location and follow links from the main page to get predictions for when Iridium flares, the International Space Station or other such objects will be visible in your area. The site also displays charts showing you where in the sky these objects will appear.

If you like to see a more earth-based and dynamic view of how any given satellite is orbiting then this real time satellite tracking web site has a mashup showing the live movement of selected satellites superimposed over the familiar Google Maps background. You can combine this view with an Iridium flare  prediction from the Heavens Above web site to get a Google Maps view of the expected track of a visible satellite too.

It is all a little geeky, but I find it reassuring to be able to get an explanation for such phenomena.

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