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Blast from the past

Astroimager Adam Block explains how to search your images for new discoveries.
RELATED TOPICS: ASTROIMAGING
AdamBlock_2013
What’s the first thing you do with CCD images you collect? Most likely, calibrating the images using biases, darks, and flats. But then what? It may not even seem like a step in the procedural list, but the answer is to simply examine the images. With disciplined attention to detail and a little luck, the universe can reward you in surprising ways.

With today’s technology we can capture many mysteries we have yet to discover in our images. The first time I examine a set of images, I am either looking for artifacts or images I can safely throw out.

With a zoom of 200 percent, I can further cull images that display poor seeing and at the same time become familiar with the field. Finally, I compare my combined images with older ones that I may have or ones on the Internet. I am always hoping to find an asteroid when my target field is nowhere near the ecliptic because this would mostly likely be an interesting object.
McNeil Nebula
Image #1. Amateur astronomer Jay McNeil discovered the nebula that would forever bear his name January 23, 2004. It lies in the reflection nebula M78 in Orion.
Adam Block/NOAO/AURA/NSF
I’m also seeking some strange variable nebula such as the one Jay McNeil noticed in 2004. Upon discovering the nebula photographically with a 3-inch refractor, Jay asked me to take one of the first high-resolution color pictures of it (Image #1). This became one of my first observations of something changing other than variable stars and asteroids.

Although you can automate the process of selecting the best images to combine, I recommend spending the time to see what is changing in them. Doing that will help you optimize your equipment as well as potentially discover something. Remember, looking closely at your data throughout your work process can lead to real discoveries.

In April 2013, I was processing data I took of NGC 6240, and I did what all astrophotographers do: compare the image to online published versions. Few pictures were of commensurate signal strength or resolution. However, I took note of the Sloan Digital Sky Survey image and a beautiful Hubble Space Telescope (HST) image of the galaxy.
NGC 6240
Image #2 compares an older shot of NGC 6240 from the Hubble Space Telescope (top) with the SkyCenter’s version, which contains the supernova designated SN 2013dc.
Top: NASA/ESA/Hubble Heritage Team/A. Evan; bottom: Adam Block/Mount Lemmon SkyCenter/University of Arizona
And it finally happened, something that I have waited for nearly 20 years — I saw something in my image that was not in any other. I had finally discovered a supernova! I was pretty confident about my find being a true supernova because the HST image showed a star-forming region in the same part of the galaxy (Image #2). Further spectroscopic observations by professional astronomers determined that this was a type IIP supernova that took place in this pair of colliding galaxies more than 400 million light-years away.

It’s only because I scoured the image and compared it with older data that I found this celestial beacon. I remember staring at the image. I was fairly certain it was unknown and that I was the only person to be privy to this event. It’s a wonderful feeling and a powerful way to connect with the universe. Later, I was doubly rewarded with the opportunity to share my excitement with the astronomy community.

Scrutinizing your images requires minimal skill and, in the case of extragalactic supernovae, modest equipment. Detecting a galaxy is sufficient to find supernovae since many tend to be brighter than the galaxy itself. Other supernova hunters have said that if you look at 1,000 galaxies each night you will probably find at least one supernova. In my case, I beat those odds: It took me 20 years after looking at a new galaxy every few weeks.

Variable stars, active galactic nuclei, unknown nebulae, gamma-ray bursts, comets, galactic star streams, and perhaps even dwarf planets in the Kuiper Belt (optimistic but possible in principle) are all additional things to keep an eye out for. All you have to do is pay attention to the subtle cosmic play that unfolds before us.
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