Two years ago this week Caltech astronomers were using the 200-inch Hale Telescope to observe the fractured Comet 73P/Schwassmann-Wachmann 3 as it came relatively close to Earth.
The comet was discovered by Arnold Schwassmann and Arno Arthur Wachmann in 1930. In 1995 the comet was found to have broken up into four fragments in 1995. By its 2006 passage it had further split into dozens, if not hundreds, of pieces.
The animated gif above shows a sequence of 15 looped images showing the in the foreground against distant stars and galaxies which appear to streak across the frame. Because the comet was moving at a different rate across the sky than the stellar background, the telescope was tracking the comet's motion and not that of the stars. Many fragments of the comet are visible as nearly stationary objects in the movie. In all, 16 new fragments were discovered as a part of the Palomar observations.
Why use a filter that passes red light to photograph each of these images? Is this to prevent over exposure or over saturation of the CCD? Also I was wondering what brought you to write about this now after two years? Just curious.
ReplyDeleteTwo years ago I wasn't blogging, but the photos & press release have been on the observatory's website since just after the observations.
ReplyDeleteI am posting a lot of anniversaries of event this year, because this is the 60th anniversary of the dedication of the Hale Telescope.
As for using just red light for the images of the comet, it could have been done for a variety of reasons. Astronomers almost always photograph through narrow-band filters. They may or may not shoot in a variety of colors and assemble a color image. In this case things were changing so fast that they shot in just one color to capture the changing seen of the comet fragments.
I was down in Balboa Park today for the annual National Astronomy Day event hosted by the Reuben H. Fleet Science Center and the San Diego Astronomy Association. A number of members were there on the Prado with their telescopes setup as part of the outreach program and to share the viewing experience with park visitors. Most of the telescopes were trained on the sun, using helium alpha, or H-alpha, filters to reduce the amount of light being collected and narrowing it to a specific band of red light emitted by hydrogen in its excited state. I asked of them the same question previously asked here and received for the most part a similar response, except for one who's insight I wanted to share with you today. He noted that since comets don't emit any light of their own -- that the light we see is actually a reflection of the Sun's light -- the red light filter may have been chosen in order to get a clearer image of the comet by limiting the collection of light to bands generally emitted by the sun, or more specifically the excited forms of hydrogen that generate the visible light given off by the sun.
ReplyDeleteI was hoping you could confirm or provide any further insight. What do you think?