RE: Satellite with side-to-side motion?

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Tue Jul 14 2009 - 05:20:55 UTC

  • Next message: Scott: "Satobs 14 July 2009"

    Tim Link wrote:
    
    > The object was very bright (I'd estimate 1 to 2 x the brightness of
    > Venus) and the brightness was steady.  It followed a straight path but
    > had a very noticeable and regular side-to-side motion.  The amplitude
    > of the apparent wobble was about 4-5x the diameter of the object or
    > more and hence was very noticeable.  The motion did not appear to be
    > symmetric (i.e. like a sine wave) but was more like a saw pattern that
    > gave the appearance that it was accelerating and decelerating.  It
    > appeared to be fairly low altitude, completely silent, and relatively
    > slow moving, taking about 4-5 min to cross the sky.
    > 
    > Here's the pertinent info:
    > Location: 47.14 N, -116.25 W (~60 miles SE of Spokane, WA)
    > Elevation: ~4850 ft.
    > Time:  ~0500 UTC, July 11, 2009 +/- ~ 0.5 hrs (~1000 PDT local time)
    > Direction of movement:  West to East, possibly slightly WNW to ESE)
    > Weather: Completely dark (before moonrise), clear and dead calm.
    > 
    > I'm assuming that this is a satellite of some sort, but have seen few
    > objects as bright, and have never seen anything in the night sky with
    > a distinctive wobbling motion.  Could anyone help identify 
    > this object?
    
    Welcome to SeeSat-L, Tim.
    
    Assuming you meant 05:00 UTC on July 12, then the International Space Station
    (satellite catalogue number 25544) appears to match in terms of time of passage,
    direction of travel and brightness:
    
    http://www.heavens-above.com/PassDetails.asp?Size=600&SatID=25544&lat=47.659&lng
    =-117.425&alt=562&loc=Spokane&TZ=PST&Date=40006.1965324575 
    
    The apparent wobbling motion is a common optical illusion, as discussed in the
    following archived post:
    
    http://www.satobs.org/seesat/Sep-1999/0151.html
    
    Ted Molczan
    
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