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

SQM Readings


SQM Graph

SQM Graph