| 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 near the zenith on a clear, moonless, night with the Sky Quality Meter is 20 - 21 mag/sq arc-sec, which agrees well with measurements obtained with my CCD cameras (19.5 to 20.6 mag/sq arc-sec; see here). Unfortunately, the sky brightness has increased one magnitude (2.5 fold) in the past 14 years.
In the SQM graph below, each data point represents the average of 15 readings taken every minute over a 15 minute period. The data are uploaded every 15 minutes between sunset and sunrise. Readings are not taken while the sun is above the horizon.
Last SQM Reading
 |
SQM Graph
 |