Natural Bridges National Monument
During my sophomore year, my family and I traveled to Natural Bridges National Monument in Utah in search of elusive “Bortle 1” skies — the darkest skies possible. The Bortle scale measures the level of darkness of a clear night sky. My family was on a road trip touring large swaths of the western U.S., so we tried to keep our astronomy gear portable and compact. We brought our Canon 6D camera equipped with a 15mm fisheye lens, an iOptron SkyTracker, a tripod, and our Unihedron Sky Quality Meter. We traveled to Natural Bridges National Monument, which was the first International Dark Sky Park designated by the International Dark-Sky Association on March 6, 2007. Natural Bridges is located in a “black zone” on Light Pollution Atlas 2006, which is described in detail in one of my other posts. Black zones indicate unspoiled areas with dark skies that are almost completely devoid of light pollution. A class 1 Bortle sky means the location is a superb dark sky site, and on clear, moonless nights under the right conditions, the zodiacal light, gegenschein, and zodiacal band can all be seen with the naked-eye. For more information regarding the Bortle Scale, the link below gives an in depth analysis about each Bortle class:
Natural Bridges is also gorgeous in daytime, with three spectacular natural sandstone arches spanning the desert floor.
Owachomo Bridge in Natural Bridges National Monument
When we visited there two years ago in August 2013, the skies were overcast when we arrived. Fortunately, the skies cleared for a couple of hours around midnight on the first night we were there, and skies were clear from sunset until after midnight on the second evening, which gave us enough time to experience pristine Bortle 1 skies and to take spectacular wide-angle photos of the northern Milky Way:
The park ranger we met there one night, Gordon Gower, told us he thinks the six points of light that are visible on the horizon in this photo are from mines on the canyon wall to the southwest. My dad thinks the yellowish glow on the southwest horizon is from the small town of Kayenta about 65 miles away. [Link to high resolution copy of this photo]
Here is the same photo with constellation lines and labels drawn in using Adobe Photoshop. [Link to high resolution copy of this photo]
On the second night of our visit, a group of about 20 people attended an outdoor presentation at the park’s visitor center by park ranger Gordon Gower. He pointed out naked eye sights and showed the group several deep sky objects through a very nice 16” Starmaster Dobsonian telescope.
We brought along a white poster board, and with the Moon and bright planets below the horizon, we were able to see the shadow of our hands on the poster board cast by light from the Milky Way in Sagittarius. In addition, we measured the intrinsic darkness of the sky using a Unihedron Sky Quality Meter (SQM-L), which read 21.91 at one point. This is the highest reading I have seen to date, and it seems to confirm my impression that Natural Bridges had the darkest skies I have ever seen.