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Comet C/1999 S4 Linear


C/1999 S4


Comet Linear S4 was the major comet of the year 2000, although it didn't become quite as bright as expected. It was at no time visible to the naked eye, at least not in Austria. It reached a maximum brightness of about 6.5 mag on July 23rd, featuring a more than 2 degrees long plasma tail in telescopes. It was also an easy binocular target.

During most of the comet's main visibility, which lasted for about two weeks, weather conditions in Austria were unfavorable; but on Saturday, July 22nd, we (my colleague Walter an I) had a lucky break in form of a clear but a bit humid night, during which I hastened to photograph the comet. Linear S4 was no more than 25 degrees degrees above the northern horizon during the complete exposure.

In the photograph you can see the comet's coma, the slightly green-turquoise shock front which points towards the sun, and two tails. The long, straight and bundled tail is the white-blue "plasma tail" which extends beyond the edge of the frame and consists of charged particles. The other broad, short and slightly red tail is called the "dust tail" and consists of dust particles which are set free by the sublimation of ice on the surface of the comet's nucleus. It angles away from the plasma tail towards the right.

Background stars are imaged as straight lines due to the comet's fast movement during the 30-minute exposure. North is up, east to the left. The image's diagonal measures about 2 degrees on the sky.

Click here to read two observation reports of that night (in German)

Exposure Data

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© 2010 Walter Koprolin