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Why are Iridium Flares so bright ?

Posted on 2012-09-05
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Last Modified: 2012-09-12
Iridium Flares are up to -8 in magnitude, whereas the much larger International Space Station is only -3 at it's brightest. Why?
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Question by:Eirman
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by:d-glitch
d-glitch earned 600 total points
ID: 38369798
They have very reflective surfaces which can reflect (and maybe ever focus) sunlight back to the ground.

     http://en.wikipedia.org/wiki/Satellite_flare
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by:d-glitch
ID: 38369806
Note that the track of a reflective flare would be quite narrow (on the order of the size of the satellite), and very hard to predict (since it depends on the attitude of the satellite).
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mark_harris231 earned 1000 total points
ID: 38369906
It is due almost exclusively to the composition and orientation of these satellites (or more specifically, the composition of the main mission antenni of the Iridium satellite - "highly reflective aluminum flat plates (treated with silver-coated Teflon for thermal control)"

Source: Why they flare

In contrast, the large flat surfaces of the ISS are primarily light absorbers (solar arrays).  The rest of the ISS is primarily curved surfaces/broken planes that don't provide as much direct reflectivity

Notably, it is relatively easy to predict the incidence of flare for the Iridium satellites based on operational data that is available.
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by:aburr
aburr earned 200 total points
ID: 38370458
see
http://www.satobs.org/iridium.html#flare
their antennas ate flat (not focused) and not covered by absorbing (solar cell) material
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by:Eirman
ID: 38371519
Thanks everyone .... I'll dish out points over the weekend.

d-glitch said ..... The track of a reflective flare would be quite narrow, and very hard to predict
www.heavens-above.com do an excellent job of precisely predicting flares for any location.
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by:d-glitch
ID: 38372487
>>  Note that the track of a reflective flare would be ... very hard to predict ...

I certainly blew that.
Nowadays  satellite positions can be calculated with military GPS accuracy and their attitudes controlled in 3D to fractions of a degree.  The rest is just geometry.

I'm so old I still think of satellites as tumbling through space.

Thanks for the heavens-above link.  Clear nights are coming.
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by:d-glitch
ID: 38372584
>>  Note that the track of a reflective flare would be quite narrow (on the order of the size of
      the satellite) ...

The heavens-above website says the track can be up to 80 km wide!!!

My answer would be correct if the sun were a point source.
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by:Eirman
ID: 38372929
To see a -8 you need to be no further than 2 Km from the center of the track.

These flares last for a few seconds only. A watch accurate to at least one second is an absolute must.

You must also know where true north is and be able to work out roughly where, for example, 210 Degrees is (SSW)

You also need to know the coordinates of your location ... right click on google maps and select "What's here"
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by:aburr
ID: 38373197
"These flares last for a few seconds only. A watch accurate to at least one second is an absolute must."

One summer many years ago shortly after the satellite system was put in orbit I was told the approximate shy location and the time for a flash. Not knowing true north and not being able to afford a super watch, I was able to see the flash. My wide  field of view and a few minutes of watching was successful.
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