21 January

Seeing measures the steadiness of the atmosphere.

Amateur astronomers use the Antoniadi scale for seeing conditions.

Eugène Antoniadi was a Greek astronomer, who lived from 1870 to 1944, famous for creating the first map of Mercury and supporting through his observations the fact that the famous canals on Mars were an optical illusion. A crater on the Moon, one on Mars and a dorsum on Mercury were named in his honour.

His seeing scale is used even today by amateur astronomers:

The scale is a five-point system, with 1 being the best seeing conditions and 5 being the worst. The actual definitions are as follows:

1. (I.) Perfect seeing, without a quiver.
2. (II.) Slight quivering of the image with moments of calm lasting several seconds.
3. (III.) Moderate seeing with larger air tremors that blur the image.
4. (IV.) Poor seeing, constant troublesome undulations of the image.
5. (V.) Very bad seeing, hardly stable enough to allow a rough sketch to be made.

Note that the scale is usually indicated by use of a Roman numeral or an ordinary number.

Darkness measures the effect of light pollution on the objects we observe in the night sky. 

The Bortle Scale was invented by  John E. Bortle who published it in the February 2001 edition of Sky & Telescope magazine to help amateur astronomers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites.

We use only red light to preserve our night vision during a Star Safari. Our camera is also very sensitive to red light and combined with all the red lights that we use to illuminate the paths for safety, turns everthing into the fabulous red you see when we take long exposure photos. In reality these are fairy lights and red light torches.