HAL Observatory Site Survey

Alpha Ridge The potential observatory site the the field between the photographer and the Spot-a-Pots. The parking area in the right background is the site of HAL's current public star parties.	Carrs Mill This shows the parking area currently used for HAL Star Parties. Potential observatory sites are on the right and the left off-screen in this photo.
West Friendship Shows one of several potential locations for the observatory.

Std Maps & Topomaps:

• Alpha Ridge Std Map (PDF)
• Alpha Ridge Topo Map (PDF)
• Carrs Mill Std Map (PDF)
• Carrs Mill Topo Map (JPG)
• West Friendship Std Map (JPG)
• West Friendship Topo Map (PDF)

Results of Wayne Baggett's Lighting Site Survey for Carrs Mill, Alpha Ridge, and West Friendship

After Joel's presentation, Wayne presented his detailed light survey results via animated PowerPoint presentation.  For those not
having access to PowerPoint a PDF version is also included. However, the animation is lost in that version. For those not having
PowerPoint but still wishing to see the animation, a free version of the PowerPoint Viewer can be downloaded here.

• Sky Brightness Report (Animated PowerPoint)
• Sky Brightness Report (PDF)

Wayne's text based commentary follows:

I have completed my preliminary sky brightness measurements for Carrs Mill, West Friendship, and Alpha Ridge parks.
The two linked PDF files contain the basic data and a plot of the sky brightness from each site.

Note that Carrs Mill and West Friendship were observed on 10/14/06, and Alpha Ridge on 10/21/06. Because the atmospheric
conditions (and hence the scattered light) could have been different on the two nights, I used a single zenith measurement from
WF on 10/21/06 to check the atmospheric differences. I found that WF was 0.06 mag/arcsec^2 brighter on 10/21/06 compared
to 10/14/06, so I have adjusted the AR values to be 0.06 mag/arcsec^2 fainter so that the comparison with CM and WF are
more reasonable. I caution you, though, to remember that this adjustment was made based on a single WF value, not the
entire set of data for WF on 10/21, so there is some uncertainty as to how the night differed. In particular, it is quite likely that
the adjustment based on the zenith data is not appropriate for the lower altitude observations; I wouldn't be surprised to find
that the lower altitudes need a larger adjustment than the zenith. At AR, the East zenith - 30 deg brightness is a difference of
1.70 mag, while for CM and WF the East zenith - 30 deg difference is only 1.27 mag. In the west, all three sites have similar
zenith - 30 deg differences, about 0.82 mag with a spread of about 0.15 mag between the three sites.

Also, in the tabular data, Table 3 includes some averages below it. The averages were computed in two different ways:
the upper average included all 16 of the data values (the zenith measurement was included 4 times) so that each altitude
contained the same number of values. This is a reasonable procedure because otherwise the three lower altitudes would be
given more weight than the darkest part of the sky, biasing the result to a brighter average. The second average (lower two
rows) include the zenith only once, so it is a true average of the independent determinations. As expected, these averages
are biased slightly brighter than the first average, but the differences between the sites are essentially the same with either
 averaging method.

The conclusions are: CM and WF are very similar in sky brightness except in the East where CM is somewhat darker.
AR is clearly an inferior location in this regard, being about 0.7 magnitude brighter in the East than the other two sites.

AR also has a somewhat brighter zenith brightness, about 0.3 mag/arcsec^2. On average, AR is about 0.4 mag/arcsec^2
brighter than CM, while WF is only about

0.05 mag/arcsec^2 brighter than CM. You have all observed at both CM and AR, so you can decide for yourself how significant
0.4 mag/arcsec^2 is for your observing.

Carrs Mill (10/14/2006)

Alpha Ridge (10/21/2006)

West Friendship (10/14/2006)