NASA A.D.S. Ground Breaking Paper

Well maybe not Nobel prize groundbreaking, but groundbreaking nonetheless.

In 2008/2009 I purchased a used SAC 7 camera. This was a modified webcam with a teensy tiny sensor. It was cooled and you could shoot FITS format images with it as well as movies. The big issue was the fact that it was a color webcam.

Now you might be saying to yourself…”Color sounds good to me.” But you would be wrong! To get color you have to put mini filters over 1/3 of the pixels on the chip. Each third is a different color. Then a mini-computer puts them together to form a color image. Why is this bad?

If you think about it, that means each color loses 2/3 of the other pixels, reducing resolution, and increasing the exposure time over a monochrome sensor. You also have no control over the spectral characteristics  of each filter. Each actual photometric filter (these are used to calculate the magnitudes of stars) have very narrow spectral features to make magnitude calculation easier. So a monochrome camera with a filter beats a color camera in photometry just about anytime.

Ever since I was a kid I wanted to be an astronomer and here I was with a telescope and camera but no filter. So an email to Arne Henden at the Naval  Observatory solved the issue. He said “why not extract the colors separately and use the Green filter to do photometry with your SAC-7.” So this I set out to do.

The attached paper outlines the procedure. In fact you can do this with any DSLR, point and shoot or even your cell phone! Since the photometric filters are so expensive and hard to come by, this is a pretty good way to get into science imaging at the bargain basement level. There is a manual that was written for DSLR but can be used for any color camera. Here is the link.

So where does the groundbreaking come in? It turns out this may have been the first magnitude observation done with a color CCD webcam! At the time it generated a lot of interest at the AAVSO headquarters because it could provide a new avenue for amateurs to cheaply contribute to science. There was a professor from a university that also presented a paper on using color cameras for photometry but no actual data. Seems like I was first.

Today this technique is used all the time by amateurs. It eliminates the need to purchase a lot of expensive equipment. Photometry can literally be done with a tripod, DSLR, Cell phone or Mirrorless camera. This allows almost everyone to become a “Citizen Scientist” and make a real contribution to science!

2009SASS___28__117T Web Cam photometry