Last updated on April 25, 2014 at 5:51 EDT
Comet Wirtanen
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Comet Wirtanen

April 22, 2005
The photo mosaic is based on a series of 3-minute exposures through a red filter, obtained with the VLT Test Camera in the evening of July 28, 1998. They were performed in a bright sky (5-day old Moon high in the sky) that resulted in some straylight due to internal reflections in the telescope. In the first three pictures (1 - 3), the very faint image of the comet (in the circles and somewhat elongated because of the motion) approaches a brighter background star from the right hand side. It is hardly visible in the next (4), since it is in front of this star, and in the last two images (5 - 6), it reappears on the left side of the star. At the time of the observations, Comet Wirtanen was 605 million kilometres (4.05 AU) from the Earth and 630 million kilometres (4.20 AU) from the Sun. The estimated magnitude is approx. 23 or beyond, i.e. over 100 times fainter than that of Wild 2. It is an impressive feat of the UT1 to observe such a faint object in such a short time and under these mediocre conditions.

Comet Wirtanen was discovered in 1948 by C. A. Wirtanen at the Lick Observatory (California, USA). With an orbital period of 5.5 years, it belongs (as Comet Wild 2 also does) to the so-called Jupiter family of comets, a class of short-period comets whose orbits are repeatedly modified by close encounters with Jupiter.