Re: Simultaneous Iridium flares

From: Edward S Light (light@argoscomp.com)
Date: Wed Mar 26 2003 - 08:43:40 EST

  • Next message: Björn Gimle: "Re: Simultaneous Iridium flares"

    Dear Robert,
    
    You recently wrote to SeeSat-L ...
    
    > From: "Robert Holdsworth" <robbonz1@xtra.co.nz>
    > To: "Seesat Explosive Address" <SeeSat-L@satobs.org>
    > Subject: Re: Simultaneous Iridium flares
    > Date: Wed, 26 Mar 2003 19:07:01 +1200
    >
    > I have not had any response to my query so far.  However I have done a web
    > search and can find no mention of any flares in such close proximity since
    > 1999!  There are a few reports of double flares but these have been much
    > greater than 1 second apart.
    >
    > I would also appreciate it if someone could calculate the separation in km
    > or miles - it seems from the respective orbits that it may have been less
    > than 100 km.
    < ... stuff deleted ... >
    >
    > Robert Holdsworth
    > (coordinates below.)
    >
    > ----- Original Message -----
    > From: "Robert Holdsworth" <robbonz1@xtra.co.nz>
    > To: "Seesat Explosive Address" <SeeSat-L@satobs.org>
    > Sent: Tuesday, March 25, 2003 10:19 PM
    > Subject: Simultaneous Iridium flares
    >
    > > This evening 25 March at 20:15 local (UTC plus 12) I observed with the
    > > naked eye simultaneous Iridium flares ....
    > >
    > > These were from Iridium 28 1997-051-E  and Iridium 94 2002-005-C
    > < ... stuff deleted ... >
    > >
    > > I would be interested to know how rare or otherwise sightings of
    > > simultaneous flares are.
    >
    
    The two Iridium satellites in question, 24948 = 97-051E = Iridium 28 and
    27374 = 02-005C = Iridium 94, are in essentially co-planar almost-circular
    orbits. The major difference is that "28" is at an average height of 483
    miles compared to "94"'s 418 miles. The result of this is a difference of
    about 2.22 minutes in the orbital periods. Put another way, Iridium 94
    "laps" Iridium 28 roughly every 74 hours (3.1 days). Thus, at any particular
    location, one would expect to see these two in the same part of the sky
    at essentially the same time every three days or so. If they are both
    properly oriented, [near-]simultaneous flares might arise.
    
    The fact that the two satellites are at least some 65 miles (105 km)
    apart, is unlikely to have a major effect on the flarings.
    
    Clear and dark skies!
    
       Ed Light
    
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