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73/P Schwassmann-Wachmann
 Comet 73/P passed exceptionally close to Earth on May 2006. It was not very bright so imaging it while speeding across the sky was a challenging task. On the other side computer processing of acquired images can create interesting views.

A meeting of young astronomers was held on the Zlin observatory from May 5th to May 8th, 2006. The meeting was focused to CCD imaging and image processing this time.

One group controls the telescope and the camera (left), other group learns how to process digital images (right)

The rare event—passing of comet 73/P Schwassmann-Wachmann very close to the M 57 Ring nebula—was predicted to the early morning of May 8th. Meeting attenders were excited by the possibility to observe such event, but the weather was rather poor. The sky was partially cloudy all the night and the transparent clouds changed the first quarter Moon into the big orange letter D on the sky. The haze, shining Moon and the intensive light pollution on the Zlin city limited the maximum visual magnitude to about 3.5.

Still, we captured the 73/P and the M 57 on the one field at dawn.

73/P and M 57 on May 8th. Animation created from 57 frames, each exposed for 30s.

73/P and M 57 on May 8th. Animation created from 57 frames, each exposed for 30s.

Sky conditions were more suitable for taking flat fields than for capturing a comet approaching the nebula. The varying brightness of the comet is caused by passing clouds. The first image was taken at 01:24 UT and the 57th (the last one of this animation) at 01:55 UT.

We can only estimate how the event would appear if it happens a few hours earlier. We created the following photo-montage to illustrate it.

73/P and M57—a combination of two independently acquired images.

73/P and M57—a combination of two independently acquired images.

Remark:

Please note the image above is a fake. Although both images were acquired at the same night (M 57 is 13 minutes exposure from 22:00 UT to 22:13 UT and 73/P is 71 minutes exposure from 00:10 UT to 01:21 UT), the image of 73/P with removed star trails was digitally merged with the M 57 nebula image. Such a close approach was not observable from our observatory and even if it would, the comet moves at angular speed approx. 15 arcseconds per minute. It is not possible to take long enough exposure of the comet without streaking the background stars.

We were more successful in imaging the comet while waiting to the final approach to M 57. The following picture is a composite of 142 individual frames, each exposed for 30 s without filter.

73/P in false colors (left) and in B&W palette (center). The median filter was applied to the right image.

73/P in false colors (left) and in B&W palette (center). The median filter was applied to the right image.

Note the jets escaping from the comet core on the above-right image. The image was processed by subtracting the aperture median to eliminate large-scale structures and to enhance small-scale details.

Every 10th frame was used to create the image below. The field of view is approximately 20' × 30' (the angular size of the full Moon). The comet passed from right to left within 70 minutes. Varying brightness of the comet is caused by the varying sky conditions among individual exposures.

Fifteen 30 s exposures of the 73/P, taken in 5 minutes interval, combined into one frame.

Fifteen 30 s exposures of the 73/P, taken in 5 minutes interval, combined into one frame.

The animation below shows all 142 frames in one sequence. The first frame was exposed at 00:05 UT and the last one at 01:22 UT. Each frame was exposed for 30 seconds. The comet shifted approx. 2.5 pixels during one exposition. Notice the satellite trail, visible on one frame as straight line crossing the field of view.

73/P animation compressing the 77 minutes long comet trip into one image.

73/P animation compressing the 77 minutes long comet trip into one image.

The same frames, only differently processed. The comet stands still and the stars are passing behind.

The same data differently processed create different animation.

The same data differently processed create different animation.

All images on this page captured by Pavel Cagas, Vaclav Pribik and Petr Cagas.

Images captured by G2-0400 CCD camera on 8" f/4 Newtonian telescope and processed in the SIMS software package.

 
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