Astronomers use the word "seeing" to describe the steadiness of the atmosphere.

     When you see the stars twinkle, the atmosphere is unsteady.  The view through your telescope won't be as clear as it could be.

     When the stars are still, without a quiver, the atmosphere is steady and you will get the best views through your telescope. 

     Transparency tells you how clear the night is by finding the faintest naked eye star visible.  Naked eye means looking at the sky without a telescope or binoculars, just your eyes.

     Steadiness:  The Antoniadi scale of seeing.  Use to describe the steadiness of the atmosphere.

I - Perfect seeing without a quiver.

II - Slight undulations, with moments of calm lasting several seconds.

III - Moderate seeing with large tremours.

IV - Poor seeing, with constant troublesome undulations.

V - Very bad seeing.

     When you have an astronomical log of your observations, you have to keep track of the seeing each night.

     You log in the transparency of the sky by the magnitude of the faintest naked eye star visible.

     You log in the steadiness by using the Antoniadi scale of seeing. 

     Keeping accurate records is very important if you find something new or if you want to keep a record of how an object changes over time.  Objects look different when the seeing conditions change.

     Astronomers often compare notes of what they saw and the seeing at the time.