From michael_umbricht at brown.edu  Wed Aug 31 14:02:31 2011
From: michael_umbricht at brown.edu (Umbricht, Michael)
Date: Wed, 31 Aug 2011 14:02:31 -0400
Subject: [Nelpag-announce] light pollution after Irene
Message-ID: <CAMV487Qj5df9yJMptSyD+wK0XQW7wwEdbEg9QBCckCjtr_QdWA@mail.gmail.com>

Here is a link to a plot of measurements from a Unihedron SQM-LE meter
located at the physics building at Brown. It is aimed at 45 degrees
altitude, facing south.

http://brown.edu/Departments/Physics/Ladd/tmp/storm2.gif

The graph shows sky brightness over Providence during 2011 with data
from the nights after the storm (during wide spread power failures)
highlighted.

The center portion of the graph is during daylight when the sensor is
overwhelmed - so there is no data.

The small red dots are all data from late April 2011 to now scatter
plotted from midnight to midnight local time. This shows clear nights
(approximate Naked Eye Limiting Magnitude around 4) and cloudy nights
(NELM between 1 and 3 or so.)

Green points are from Sunday showing the cloud cover during the storm
but the sky then gets very dark when the clouds pass after 22:00 on
the night of the 28th.

The graph continues with blue points for the 29th showing darker sky conditions.

Finally we have the magenta points from the 30th and cyan points from
the morning of the 31st by which time power had been restored to most
neighborhoods and the sky brightness has returned to usual levels.

-mikeu

Michael Umbricht

Ladd Observatory
Department of Physics
Brown University