[AZ-Observing] ISS This Morning: Single Frame
- From: Tom Polakis <tpolakis@xxxxxxx>
- To: AZ-Observing@xxxxxxxxxxxxx
- Date: Wed, 2 Oct 2013 12:07:36 -0400
The Space Station made a favorable flyby this morning, so I shot some video
with the webcam setup. Jenn did the tracking through the Telrad, while I made
adjustments at the laptop computer. First, some numbers that describe why this
remains challenging.
In order to get a decent image scale, you need several thousand millimeters of
focal length. With a 10" and a Barlow effectively working at about 2.5x
(3500mm f.l.), the ISS occupies over 200 pixels of the frame at close approach.
The problem is that it's moving at over a degree per second. In order to keep
image smear due to motion less than 2 arcseconds, the shutter speed has to be
1/2000 second. This means that even when the ISS is magnitude -3, it's pretty
faint when it's imaged at f/14, and requires the gain to be turned up to 11.
Now you may think that you're good at wielding a Telrad, but that 1/2-degree
inner ring is gigantic when compared to the frame's field of view of only 3.5'
by 2.6'. And it takes the ISS less than 1/15 second to cross the long axis of
the camera frame.
All of that is a disclaimer for the noise in this image, which was taken near
close approach. For scale, there are eight pairs of solar panels, and those
thin vertical gaps between the pairs are about 8 feet in width, which
corresponds with about 1 arcsecond at the distance of 300 miles.
http://www.pbase.com/polakis/image/152678525
Tonight, I should be able to put together a time-lapse showing its changing
orientation as it flew by. I promise that the message pointing to that image
will contain far fewer numbers than this one.
Tom
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