Uranus

This picture is a composite of five images taken in August 2000. Each of the 5 images is itself a composite of individual 10 or 20 second exposures. Total exposures varied from 70 seconds to 140 seconds. I used the shorter times to keep the over exposure of Uranus to a minimum. 

Once I had the 5 frames I joined them together by matching stars on their edges to give a record of Uranus's movements and those of its attendant satellites. 

To get the positions  for Uranus and its four moons Ariel, Umbriel, Titania, and Oberon I connected to http://ssd.jpl.nasa.gov/horizons.html and used the WWW ephemeris generation option. I then needed to calibrate my image so that I could plot the lines marking the trajectories predicted by JPL. This calibration essentially tells you what the RA and Declination are for every pixel in the picture and I used reference stars from the Hubble Guide Star catalogue to achieve it. During this 6 day period Uranus has moved 14 arcminutes or about half the apparent size of the moon in the sky.  

Neptune and its largest moon Triton at 22:30 on 19/08/00. Exposure 95seconds at f6.3. 

Pluto

Pluto 29/05/01 22:16UTC. Exposure 60 seconds at f6.3, Image size is 6x8 arc minutes approximately. 

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