Orion StarBlast 4.5 Instruction Manual page 15

"Seeing" and Transparency
Atmospheric conditions vary significantly from night to night. "Seeing" refers to the steadiness
of the Earth's atmosphere at a given time. In conditions of poor seeing, atmospheric turbulence
causes objects viewed through the telescope to "boil".
In conditions of good seeing, star twinkling is minimal and images appear steady in the eyepiece.
Seeing is best overhead, worst at the horizon. Good "transparency" is especially important for
observing faint objects. Transparency is judged by the magnitude of the faintest stars you can see
with the unaided eye (Mag.1 is very bright, 2 is dimmer, and so on... 4th magnitude or fainter is
desirable).
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When To Go Observing
Looking at the Little Dipper will show you how good the
viewing is. If you can see all the stars, you are doing pretty
well. Be sure to wait until your eyes adapt to the dark. Use the
guides on the next page to determine your conditions.