This negative photo shows the faint image of periodic comet Halley (in the circle) at the record heliocentric distance 18.82 AU (= 2,820 million km, about the distance of Uranus). It was obtained with the SuSI CCD camera at the ESO 3.58 m New Technology Telescope (NTT) during the night of January 10--11, 1994.
Nine individual exposures, each lasting 25 minutes, were used to produce this picture. They were cleaned to remove various sky and instrumental noise, shifted according to the predicted motion of the comet and then co-added. This ensures that all recorded light from the comet is concentrated in one place. At the same time, the images of the other objects that do not share the motion of the comet, are not superposed and will therefore be seen as long trails. The non-uniformities of these trails arise because of varying sky conditions and also due to the time intervals between the individual exposures.
In addition to the comet, the picture contains the images of three very different types of objects: stars with relatively sharp trails (e.g. the comparatively bright one, just below the comet image), several extended (diffuse) galaxies, and an artificial Earth satellite which happened to cross the field during one of the exposures (its trail extends from the middle of the left edge to the lower edge).
The measured magnitude of P/Halley is V = 26.5 +-0.2. The position in the sky is less than 1 arcsec from that predicted on the basis of the comet's very well-determined orbit.
Technical information: The CCD frames were cleaned of cosmics and flat-fielded, but they were neither filtered, nor smoothed. Total exposure time: 13,500 seconds. The seeing varied from 0.6 - 0.9 arcsec. One pixel = 0.13 arcsec. Field size: 310 x 430 pixels or 40 x 56 arcsec. North is up and East is to the left.
This photo (ESO PR PHOTO 04/94-1) accompanies ESO Press Release 04/94 and may be reproduced, if credit is given to the European Southern Observatory