Re: Daytime Iridium Flares?

From: ComHem (
Date: Tue Apr 03 2007 - 03:54:26 EDT

  • Next message: Peter Wakelin: "SATOBS 2007 April 02"

    To add a few tips to Jim Scotti's:
    If the air is clear/clean, 90 degrees (or more?) away from the Sun
    the sky is dark enough.
    In any case, try to find a spot where the Sun is blocked
    by a house or dense trees.
    Timing is essential - if I strain my neck more than a few
    seconds (in daylight only?!) I see many short flashes.
    For the right spot in the sky I have often used a compass
    and an adjustable angle finder with a spirit level, well in advance.
    If you can find a place shadowed from the Sun, where
    you have a marker near the expected spot, like a TV antenna
    or a chimney, the corner of a roof , or a tree top, note the place 
    I have some times used George Roberts' suggestion:
    On a night in advance, you can use a planetarium program
    to find a star at the right position, then locate the marker described 
    You can find the RA/Decl. of the flare if you use Rob's SkyMap
    or IridFlar. [Heavens-Above won't show you a star map
    for daytime flares, but you could convert the az/alt
    mathematically or using a planetarium program]
    Then find a reference star at the "same" declination
    and note the R.A. difference. If the star is at a lower
    RA, subtract this time diff from the flare time (add if larger).
    Subtract 23h56m as (many times as) needed.
    This gives the time you should go out to find your marker.
    Observer's Location:  Bruce MacDonald ( 51.3440N, 1.9849W)
    Local Time:  British Summer Time (GMT + 1:00)
    _______________(Mag.) Flare position Flare _____centre Sun 
    _____________________Alt.Azimuth  Distance ________Mag Alt.Azimuth From 
    04 Apr 18:23:08 -8.1 71 324 (NW ) _1.6 km (W) __-8.2 12 264 (W ) 69 
    Iridium 91
    (69 degrees from Sun makes a polarizer possible)
    71 deg high makes finding a marker a bit hard, but remember
    it feels like 90, if you are not lying flat on the ground!
    With az=324 I have RA=04:18, Dec=+64.8
    (SkyMap for flare time)
    There are no bright stars at convenient hours tonight,
    alpha UMa is close enough, but at 00:35 local time it will be 5 deg above 
    the flare pos.
    At 22:45 you have the two stars (mag +4.5/+5.5 five deg. of omi UMA at 
    08:41, +64.3) there.
    Note: Heavens-Above has
    27373   Iridium 91
    SpaceTrack has:
    27373   Iridium 90 has (March 06):
    27372   Iridium 91     ?        Spare   was called Iridium 90
     27373   Iridium 90     ?        Moving between planes (Oct. 2005) was 
    called I 91
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