Wednesday, March 24, 2010

The Big Boy Star Chart

A couple posts ago I was looking for the identification of some objects near the Hyades star cluster. After some hints from a Tucson Amateur Astronomy Association (TAAA) member, one of the objects was found to be LDN1551. As the owner of several paper star charts that did not identify them, I was hoping to get to the Science Library at UA or to the Kitt Peak headquarters library to use the Palomar Observatory Sky Survey (POSS). The original POSS were prints of images taken with the 48" Schmidt Telescope back 55 years ago, and since my college days revelled in using the photographic prints to vicariously observe pretty much all there was to see in the sky. In my Kitt Peak days, not only were they used routinely by professional astronomers to make their finder charts to use at the telescope, but besides the photographic print version, there was a glass plate version which provided a truer replica of the original glass plates used in the original survey. In the '90s with finer-grained emulsions, the POSS-II was done over the course of a decade and reached fainter objects, even with the growing light pollution near Palomar.

Today I was able to get away at lunch and made the 200 meter walk to the NOAO offices and found the POSS down in the bowels of the library extension in the basement. The 1000 print pairs (red and blue exposures of the same field) fill a large file cabinet. What made them even more useful back in the '80s was a transparent overlay which labelled nearly everything in the exposure. Shown here is the blue light exposure of the Andromeda Galaxy and repeated with the overlay in place. There are lots of lil' objects there, dominated by globular clusters and a myriad of other things.

So I found the chart showing the Hyades, but in reality, my picture of the little dark clouds (admittedly windowed a little severely here), only barely showed up in the print version of POSS-I, likely printed to show stellar objects better.

However, this afternoon, while Googling the POSS, I found that digital versions are online for anyone to use, with any version of the Sky Survey, including a near infrared version that was part of the latest '90s edition. So I typed in LDN1551 and include the image here - a red exposure from POSS-II. Only a 1 degree square maximum is allowed, but a good comparison can be made. Both images are shown with north to the right. I'm still impressed what the little 135mm lens (2 hour exposure @F/4) did compared to a major observatory instrument, but it was also nice to find the on-line versions of all the Palomar Observatory Sky Survey editions at the click of a finger!


David A. Harvey said...

Very cool!

David Oesper said...

I like the user interface better than SIMBAD. This one's a keeper and I have it bookmarked. Thanks, Dean!