Built on Facts


I have a project for you, since I know practical physics is pretty popular around here. This one involves orbital dynamics, optics, and astronomy. The required experimental apparatus is just your eyes, a clock, and an internet connection.

There are these satellites orbiting overhead by the name of the Iridium constellation, working diligently to provide various communications services to its customers. We’re not so interested in that. What we are interested in is the fact that these satellites have highly reflective mirror-like antennas which reflect sunlight down to the earth. With a little geometry done for you automatically online, you can predict exactly when these beams of reflected sunlight will intersect your position. Some of them are bright, in some cases many times brighter than the brightest stars. All you have to do is input your position, set your watch to the next flare, and walk outside to see it.

It seems pretty trivial, but it’s quite a demonstration of the power of physics that such an event can seem trivial in the first place. Give it a shot, I promise it’s really cool.


  1. #1 rob
    April 9, 2009

    i think i saw one by accident a couple weeks ago. i was walking my dog at night, looked up hoping for a meteor and saw a *bright* satellite. it faded then brightened up again about a minute later, then faded out completely. i was told it was probably an iridium flare. very cool.

  2. #2 Tom S.
    April 9, 2009

    I’ve been viewing the iridium satellites, with the help of heavens-above.com, for a couple of years now. It’s fun showing them to the kids in the neighborhood. The adults enjoy it as well.

  3. #3 joulesm
    April 9, 2009

    whoa thank you!! this is probably the coolest thing i’ve seen this week šŸ˜›

  4. #4 PalMD
    April 9, 2009

    OK, if the clouds actually clear in SE Michigan, i’m definitely gonna do it…

  5. #5 magista
    April 9, 2009

    I’ve got a -7 mag flare coming up at 03:30 Friday, and a holy crap! -9 on Saturday at 06:30. Yowza!

  6. #6 scott
    April 9, 2009

    Just got back from capturing a magnitude -7 event. Thanks for the referral! It was a cloudy evening, but the light cut through the clouds and we were able to capture this image:

    Polaris was visible just to the left of the event, so it was easy to set up the shot beforehand. Undoubtedly the coolest thing I’ve seen in a while.

  7. #7 pkoen
    April 11, 2009

    Is there something wrong with the Heavens-Above.com website since about 8 April 2009??? Every time I try it, I get “Connection Interrupted
    The document contains no data.”

  8. #8 joulesm
    April 13, 2009

    Now we just need someone to write an iphone App for this…

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