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 > > ----------------------------------------------------------------- > To unsubscribe from SeeSat-L, send a message with 'unsubscribe' > in the SUBJECT to SeeSat-L-request@satobs.org > List archived at http://www.satobs.org/seesat/seesatindex.html > > ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
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