Some people who have never seen a
comet think that they streak through the sky like meteors. In reality, although comets are often
moving very fast, they are so far away from us that they seem to be stationary observed
with the naked eye. Through a telescope,
however, the movement of a comet can be seen against the background stars by
watching it for several minutes. Observing this movement is how comet hunters know that they have found a
comet and not a dim galaxy or nebula.
This sequence of 11 telescopic images of one part of Comet Schwassmann-Wachmann 3 shows its slow movement against the background stars over a period of 11 minutes on the evening of April 29, 2006. This comet was discovered in 1930, and it orbits the Sun once every 5.34 years, so it is called a periodic comet. During its approach to the Sun in 1995, the comet broke into several pieces, and one of the two largest pieces is seen in these pictures. In the spring of 2006, the two largest pieces looked like two separate comets several degrees apart in the sky, each sporting its own tail. A few smaller pieces were observed as well. Some of these pieces were seen breaking up into many smaller parts. It should be interesting to see what is left of the comet when it next approaches the Earth in 2011.
The white diagonal line in the third frame of the sequence is probably an earth-orbiting satellite that happened to pass through the field of view as that picture was being taken.
Image details: Eleven 60-second exposures at ISO 400 with a Nikon Coolpix 5000 camera through a Meade 12-inch telescope, using eyepiece projection with a Celestron Ultima 45-mm eyepiece.