Re: [dsat] Resurs 1-3 Solar transit

From: John Locker (john@satcom.freeserve.co.uk)
Date: Mon May 12 2003 - 11:19:19 EDT

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    Just one more point on this Bjorn....
    
    What we havnt taken into account is atmospheric turbulence. "seeing"
    
    When imaging say  , Jupiter , I will take an avi of perhaps 5-600 frames ,
    and then select the best 50-200 of those to stack , which brings out more
    detail.
    If I am imaging at the time of a shadow transit by one of the moons , the
    small shadow may fade in and out of the frames due to poor seeing
    conditions.
    
    When imaging a solar transit , the effects of seeing are going to be much
    greater because the actual time period of the transit is so small , the
    target  might only be a single  pixel in size , and the turbulence from the
    sun itself will have an effect (this is apparent when trying to image even
    the largest sun spot).
    
    I would estimate seeing to have been no better than 3/10 when I imaged
    Resurs 1-3 and perhaps a little better last week when I captured the Cosmos
    rcocket body.
    
    I suppose taking all this into account it's surprising the object ever
    registers at all :O)
    
    Regards,
    
    John.
    
    Subject: Re: [dsat] Resurs 1-3 Solar transit
    
    
    > If transit took 0.86s, why don't you see it in more than one frame at 15
    > fps ?
    >
    > Does the Sun fill your webcam image (or what % of the image/Sun)?
    > If your webcam delivers 480 vertical pixels, and the Sun (apparent size
    > 18 km at 2000 km range) fills the image, the distance between pixels is
    > 36 m.
    >
    > So a smaller rocket (also moving 5 m during exposure) would not always be
    > completely within a pixel, and then only reduce the image intensity to
    > some 90%, not completely black, but it would of course look as big as one
    > pixel.
    >
    > ----- Original Message -----
    > > It passed across the lower half of the Sun's disk at 18:30:26 gmt
    > appearing
    > > in one frame of AVI (1/2500th sec 15fps ) as a small blur traversing
    > north
    > > of the main sunspot cluster , presently visible.
    > >
    > > I was using a webcam / 200 mm zoom lens combination fitted with Baader
    > solar
    > ...
    > >
    > > I am however uncomfortable with the size of the target.
    > > Last week I imaged a solar transit by a Cosmos rocket booster using the
    > same
    > > set-up.Again , the object seemed to be too large....so I have a couple
    > of
    > > questions.
    > >
    > ...
    > > what causes this apparent magnification.....the booster is after all
    > only
    > > 10.4 metres in length and has a range of nearly 2000 km.
    > >
    > > Details from CalSky.com are as follows.
    > >
    > > 19h30m29.4s Resurs 1-3 Rocket
    > > (23343 1994-74-B) Crosses the disk of Sun. Separation:0.25d
    > > Angular Velocity:12.9'/s.  Transit duration: 0.86s
    >
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