| Sky Quality Meter |
Shown below is the sky brightness measured with a Unihedron Sky Quality Meter (SQM). The larger the number, the darker the sky. The darkest the sky can get absent any man-made light is about 22.0 magnitudes/square arc-sec, which is equivalent to a magnitude 22 star every square arc-sec in the sky. For reference, the sky brightness (V-band) at various dark sites is: Mauna Kea Observatories in Hawaii (elevation 13,800 ft)- 21.3 to 21.9 mag/sq arc-sec; Mount Lemmon Observatory in Tucson, AZ (9,150 ft)- 21.5 mag/sq arc-sec; New Mexico Skies in Cloudcroft, NM (7,300 ft)- 21.4 mag/sq arc-sec. A difference of 1 unit of sky brightness equals a 2.5 fold difference.
The sky brightness at my observatory measured on a clear, moonless, night with the Sky Quality Meter is ~20.5 mag/sq arc-sec, which agrees well with measurements obtained with my CCD cameras (20.1 to 21.0 mag/sq arc-sec; see here).
In the SQM graph below, each data point represents the average of 5 readings taken every minute over a 5 minute period. The data are uploaded every 5 minutes between sunset and sunrise. Readings are not taken while the sun is above the horizon.
Last SQM Reading
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SQM Graph
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