University of London Observatory
[Comet Ikeya-Zhang]
Images of Comet Ikeya-Zhang

These images of Comet Ikeya-Zhang were obtained at the University of London Observatory with the Radcliffe 24-inch refracting telescope using a (red) filter which selectively passes the light emitted by ionized water molecules (H2O+) in the comet's plasma tail.

The light from these water ions can be seen tracing the filaments of gas trailing the cometary nucleus. The water molecules are released from the surface of the comet as the ices in the cometary nucleus evaporate. They are then ionized by radiation from the Sun, and get `blown' away from the nucleus by the solar wind of ionized particles streaming away from the Sun.

(The H2O+ filter used is an interference filter with central wavelength 620.5 nm and bandwidth 5 nm.)

The images show a region close in to the nucleus, covering about 10 arcminutes on the sky.

This corresponds to a region about 200,000 km across at the distance of the comet, equivalent to about 15 Earth diameters. In contrast, the nucleus itself is probably only a few kilometres in size.

The streaks in the images are stars which have been trailed by the telescope as it was guided on the comet's motion during the exposure.

Images taken with the Radcliffe 24-inch telescope at the University of London Observatory, Mill Hill.
All images are credit and copyright University College London (UCL)

Click on the images for a bigger version. North is up and East is to the left.

2002 March 26

Observers: Steve Fossey and Chris Clark

UT 1957, 300 second exposure. UT 2003, 300 second exposure.
Co-added 2 x 300s exposures.
UT 2012, 300 second exposure.

The final image was obtained 15 minutes after the first one shown above. Even over this short timescale, the structure in the rays is seen to change: a time-lapse sequence of these 3 images shows the rays folding inwards, and new rays forming.

The image below is the first image above, after application of an unsharp mask to reveal fine-scale structure. Structure in the inner coma can be seen, providing information on the emission of dust grains from the nucleus. The comparison of time-separated images hints at evidence for rotation of the nucleus.
UT 1957, 300 second exposure, unsharp masked

2002 April 04

Observer: Steve Fossey

The first image shown below is the sum of nine 300s exposures. The animated GIFs show the comet's motion over about half an hour: the folding inward of the ion tail over this interval can be made out. The first animation loops through 3 frames derived from a total of 6-7 co-added 300s exposures. The second cycles through the same 300s exposures, one at a time.

Nine co-added 300 second exposures.
Animated GIF: 3 x co-added 300s exposures (600k).
Animated GIF: 7 x 300 second exposures (1400k).

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This page maintained by Steve Fossey.
Last updated: 2002 April 09