Astrophotography in Cleveland   Leave a comment

Cleveland is not known for the quality of the night sky. In fact, the combination of city lights and high humidity make visibility quite poor. Even so, we can use physics to tweeze out signal photons from the background noise. Here are some images (approximately 1/2 the total image size) of the Ring Nebula (M57), the Whirlpool Galaxy, and the Sombrero galaxy:

These images were assembled by ‘stacking’ many (many, many, many) frames together. The Whirlpool galaxy image resulted from stacking together over 3000 images, for example. Stacking increases the signal-to-noise ratio for two reasons. First, since we don’t have a tracking mount, our exposure times are limited due to the rotation of the Earth- 0.8 seconds is about the longest exposure before stars stop being points and start looking like dashes. Stacking lets us go from a 0.8 second exposure time to minutes or hours (although, a 1 hour exposure represents over 4000 images…). Second, stacking lets us separate signal photons, which are constant, from noise photons, which fluctuate and obey Poisson statistics. Stacking together many frames lets us ignore the fluctuating noise and keep only the signal- the Whirlpool galaxy image has stars as faint as magnitude 15 in it.

To be sure, implementation of the stacking algorithm is not simple- frames have to be moved and rotated into alignment, and there is a lot of image processing on each frame to determine the location of stars (which move around from frame-to-frame due to atmospheric clear-air turbulence). We use freeware (DeepSkyStacker) for all of our astrophotography.

Ok- enough of that- here are some of the goodies hidden in the images above: NGC5229, a low-surface brightness galaxy

a few other galaxies: NGC 5198 and IC 4263/NGC 5169/NGC 5173

And finally: the Orion nebula


Posted May 8, 2012 by resnicklab in Physics, pic of the moment, Science

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