COMING SOON - Pine Mountain Club - Mt. Pinos Sky Quality Meter
The Sky Quality Meter gives measurements of how dark the night sky is
at our observing location in Pine Mountain Club. The meter measures
the brightness of the sky, and reports it as a "magnitude per square
arc second" (also called "mpss"). As such, a reading of 20.0 mpss
means that the brightness of the sky is the same as if you took the
light from a single star that was magnitude 20.0 and spread it over an
area of sky that was a square with dimensions of 1 arc second by 1
In astronomy, larger star magnitudes mean that a star is dimmer. As
such, the very bright star, Spica, has a magnitude of 1.0 and is
easily visible from a large metropolitan city. Conversely, the
faintest stars people with good eyes can see from a dark location are
about magnitude 6.
So, the ideal dark sky for doing astronomical work will have a large
mpss. In fact, the darkest skies have an mpss value of about 22.
Typical mpss readings for suburban locations will be about 19, and the
center of major cities will have mpss readings around 17.
This chart shows the SQM-LE readings from Scott and Barbara Rosen's
SQM-LE in Pine Mountain Club. The meter is pointed just southeast of
the zenith (directly overhead), so it is looking right over the top of
Mt. Pinos. To see a history of SQM readings, click on the chart for
daily, weekly, and monthly graphs.