Light Pollution Test

Date: October 16-31
Time: 7:00 pm, one hour after sunset
Place: the eastern sky

Pegasus is the winged horse of Greek mythology. As with many other constellations, its fainter stars have been rendered invisible by light pollution. Only an easy asterism remains. Asterisms are subsets of the main constellation that look like something familiar, and for Pegasus that would be the “Great Square.”

This asterism is striking for its (at first glance) lack of any stars inside the Square.  In fact, there are 13 stars in the Square brighter than magnitude +6.0, the normal limit for unaided, dark-adapted, human eyes.

If you can find the Square, let’s do a simple test to measure the darkness of your night sky.  Turn off all your outside lighting. Go outside and find a comfortable spot to observe the eastern sky. Give your eyes at least 15-20 minutes to adjust to the darkness. Relax. Enjoy the view of the sky as your eyes tune-in to the lower light level.

Now, count the stars you can see inside the Square and you will have a good measure of the quality of your night sky.  If you can see 7 of these stars, congratulations! You have a darker-than-average night sky. If you see less than 7 stars, time to talk to your neighbors about their outside lighting.

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