Photo samples: C/1980 Y2 (Panther)


Photo samples: C/1980 Y2 (Panther)


      Comet Panther was one of those typical comets that never became especially bright. Although I obtained a number of observations of it, it was not a comet I was planning on photographing, as I had never photographed a comet that faint before. As it turned out, this comet's path across the sky put it in an unusual position on March 11 and 12, as it threaded its way through the narrow space that separated Polaris, the "North Star", from the actual celestial north pole. The celestial north pole marks the point of the sky that is always in the same direction and same altitude day in and day out, month after month and year after year. It is the direction Earth's own imaginary axis points toward in space and, as Earth rotates, the stars appear to move around this point.
      Any time a camera is simply pointed at the night sky with its shutter open for a period of time, the stars will form trails on the film because of Earth's rotation. But depending on where you point the camera makes a big difference on how long the trails will be after a particular period of time. A camera pointed at the celestial equator will produce very long and straight trails, while a camera pointed at the celestial north pole will produce very short, curved trails. The closer to the celestial north pole you get, the shorter the trails. This also means objects near the celestial north pole are spending more time on a particular area of your film. This gave me an idea. Since comet Panther was passing very close to the celestial north pole, it should move very little during long exposures. So, on the nights of March 11 and March 12 I made exposures that were one hour in duration. What's more, the camera was simply placed on a tripod, with absolutely no guiding. I knew the stars would trail, but I was hoping the comet would trail very little and show itself on the film.


This image is a digital combination of two images I obtained on 1981 March 11 and March 12 UT. I used Fuji 400 and a 205mm lens set to f/5.6. The exposure each night was one hour, but the camera was simply put on a tripod and was not guided with the stars. The result was my first photographic detection of a 9th-magnitude comet. Although the comet did trail slightly during the exposures, the fact that it was so close to the celestial north pole caused its light to spend more time on the film grains than if it had been anywhere else in the sky. Polaris is the bright trail in the image, and the star trails help indicate the location of the celestial north pole itself.