The Beautiful Ion Tail of Comet Hyakutake
15 March 1996
Following recent observations at the ESO La Silla Observatory, there is now no doubt that Comet Hyakutake - as hoped - is developing into a major object! In any case, the observed, very complex structure as well as the extent of the tail system is typical of a bright and beautiful comet.
This is the provisional version of an image of Comet Hyakutake, obtained by Guido Pizarro (ESO) with the 1-metre Schmidt telescope at the La Silla Observatory. The exposure was made on sensitized Kodak 4415 film behind a GG385 filtre. It began on March 14, 1996 at 06:00 UT and lasted 26 min. The telescope was guided on the comet during the exposure and the star images are therefore trailed. North is up and East is to the left.
The film was digitized by means of a small CCD camera at La Silla and the image was transferred to the Headquarters in Garching via ESO's intercontinental computer link. While this procedure ensures an early availability of the image for a rough evaluation (and allows to put it on the Web as soon as possible), the original image sharpness (angular resolution) of a large Schmidt exposure (about 30,000 x 30,000 pixels) can of course not be preserved in this version. The films are on their way to Garching and it is expected that an improved version will become available on March 19, after the necessary photographic processing.
The field shown here covers about 2.8 x 2.1 degrees on the sky. On this relatively deep exposure, the comet head measures approx. 35 arcmin across. The part of the extensive ion tail that is visible on this reproduction is characterised by a complex structure, with many streamers extending from the head towards the West. The main part of this tail has the typical wavy structure with several bifurcations. All of this is caused by the interaction between the ions in the tail and the 'turbulent' interplanetary magnetic field.
The dust tail is not well visible on this photo, but on a 60 min exposure obtained in moonlight with the same telescope just after the present one, a broad, fan-shaped dust tail is easily perceivable. It reaches to the plate border, about 5 degrees from the comet head and measures almost 2 degrees across at this distance. On the same film, the ion tail also extends to the border and is seen to have two main branches which separate approx. 2 degrees from the head.
This is the caption to ESO Press Photo eso9621. It is available in four versions [Positive,GIF,424k], [Positive,GIF,88k], [Negative,GIF,352k], [Negative,GIF,77k] ('positive' indicates white stars on a black background; 'negative' black stars on a bright background, i.e. as on the original film).