Where Do You Build An Observatory?

On a crisp Bedford County day in early 2007, I walked slowly around a ridge in the middle of a cleared field at Lynchburg College’s Claytor Nature Study Center. The ridge was the highest point on the property, but I wanted to be sure the view was such that tree lines in all directions were as low as I could get them. Walking in small circles, finally I stopped and said (apologies to Brigham Young), “This is the place.” The pier for the Margaret Gilbert telescope at the Belk Observatory now stands under a dome at that spot.

What makes a good spot for an observatory? First of course, you need to own the land or at least have permission to build on it. When Lynchburg College was gifted with the Claytor property in 1998, it provided both the land and the dark skies that an observatory needs. LC’s gorgeous campus doesn’t really have the space—even I wouldn’t dream of putting an observatory in the Dell—and the lighting on and around our campus means much of the sky would simply be washed out. So two factors are obvious and were met by our Bedford county site: relatively unobstructed views and relatively dark skies. What other factors are important, and what makes for an “ideal” location for an observatory?

  • Clear skies: There is a reason that there are no world-class observatories east of the Mississippi River. Our cloudy and rainy summer of 2013 has been especially frustrating as we seek to calibrate our telescope and open the facility to the public. The more clear nights, the better your chances of seeing the sky.  You can see from the image below why there are major observatories in Southern California and Arizona, and not in Cleveland, Buffalo, or Portland!

Annual Mean Number of Cloudy Days Sunrise to Sunset

  • Altitude: The higher you are, the less of the atmosphere you have to look through, and the atmosphere both obscures and blurs. While it is transparent to visible light, air does scatter light, and even a very dark sky at sea level is brighter than the absolute black of deep space. At its extreme, the sky is blue and bright during the day, preventing our seeing the stars. So not just a location in Arizona, but a mountaintop in Arizona.

Kitt Peak

  • Atmospheric Seeing: It’s more than just the absence of clouds. Even when there are no clouds, there can be enough water vapor in the air to diminish its transparency and make it more difficult to see dim objects. And even clear dry air can be turbulent and unsteady because of temperature irregularities. Air at different temperatures has different densities and bends light differently. If the temperature does not change smoothly with altitude, a star that is a pinpoint under good conditions is degraded into a shimmering blob. The “micro-climate” of a particular location can be crucial to the average seeing.

atmospheric seeing

  • Dark skies: Locating near an automobile dealership or a large mall is definitely not advisable! While the Belk Observatory has the darkest skies in our area, they are certainly not the darkest available anywhere. A wonderful zoomable light pollution map can be found here, and it’s not difficult at all to pick out major urban areas, even not-so-major ones.  In an image from this map showing the area near the observatory, you can see that we are just barely in the green (the mean position between most and least light polluted) beyond the lights of Bedford City. The observatory is at the end of the road leading to the right off Cloverlea Lane.

Observatory Light Pollution

Here is a high-resolution image showing the entire US by county.

light-pollution-us

  • Access to much of the sky: Where you are on the Earth’s surface determines what portion of the sky you can actually see. Not only are regions at high latitudes often too cold and stormy, they also are limited to the southern or northern half of the sky plus a little more, depending on how close to the equator they are. At the equator, both the northern and southern halves are visible, but objects near either celestial pole would be right at the horizon. Ideally we would have telescopes in both hemispheres to provide full coverage.

So where are the premier astronomical sites in the world? For the Northern Hemisphere, the summit of Mauna Kea on the island of Hawaii has been the site of many of the world’s premier optical telescopes for some time. At 13,800 feet, it is not only above much of the atmosphere, it is above most of Hawaii’s changeable weather.

Mauna Kea obervatories

For the Southern Hemisphere, the Andean Mountains provide a rain shield for a region in Chile that is one of the driest on Earth. The Atacama Desert is the home of, among many other instruments, the Very Large Telescope. I know—astronomers are so imaginative in their nomenclature. This is an array of four large telescopes that can be used separately or together to achieve very high resolution (sharp detail).

Bird?s Eye View of the Very Large Telescope*

So: are we happy with our 0.5-meter telescope, located at 960 feet altitude, in a place with 43 inches of average annual rainfall and 60% non-cloudy days? You betcha!

Belk Observatory

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