Sycorax, or Uranus XVII


Sycorax was discovered with the 5m Hale telescope at Palomar in September 1997 just over 21 years before this image was taken on 2018-11-08. The satellite is only 150 km in diameter and was 2967 million km distant at that time. It then had a V magnitude of 20.5 and is only just detectable on this image. Sycorax is circled in the inset image; star 'D' has a Gaia G-magnitude of 20.66 and 'g' is a 19th magnitude background galaxy. Despite a signal to noise ratio of less than 4, I was able to measure a position good to about 0.2 arcsecs which agrees well with the published ephemeris.

The background glow at the bottom-centre of the image comes from Uranus itself and the streaks at the top-right are due to a sixth-magnitude star, each of which were carefully placed outside the frame.

Image information
Date and time of observation  2018-11-08 23:05 UT
Telescope 0.4m f/6.5 Dilworth-Relay
Filter None
Exposure 3×30s+4×300s+3×600s median-stacked
Centre of image RA 01h51m58.0s  Dec +10°56'56"
Image dimensions 10.0 arcmin × 17.3 arcmin