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Terry R. Friedrichsen
Bunker Ranch Observatory
The rural areas of Hidalgo County and the surrounding area are prized by astronomers, both amateur and professional. There are a number of mountaintop professional observatories nearby, and the area is well known to amateur astronomers as well. There are several private amateur observatories in the area, and even an entire subdivision devoted to amateur astronomers and their facilities in nearby Portal, Arizona. Also, amateur astronomers from all over the world come here to photograph the night sky from such accessible mountaintop areas such as the Chiricahua Mountains and the Cloudcroft area near Alamogordo.
What draws astronomers here? There are 3 factors: the sky must be dark, transparent, and steady.
Large metropolitan areas throw lots of light into the sky. Even Tucson, Arizona, with strict light-control ordinances to protect the nearby observatories (such as the Kitt Peak National Observatory), produces a glow that is easily visible even dozens of miles away. For astronomy, it is desirable to be at least 100 miles from large cities. The towns of Hidalgo County contribute little to such "light pollution", making the night sky a spectacular sight.
A dark sky isn't helpful if you can't see through it. The high-desert climate of Hidalgo County yields many clear, cloudless nights for viewing the stars, and the pollution-free skies mean that you can see for dozens of miles all around. When you're looking up at the stars, you're only looking through a few miles of the atmosphere, so the fact that you can see much farther than that in the daytime means there is very little obscuration between you and the night sky. Mountaintop astronomy is preferred because it raises the observatory thousands of feet above the atmosphere. But in places like Hidalgo County, this isn't a necessity for amateur astronomers. And Hidalgo County is already above about 4,000 feet, which means that much less atmosphere to look through.
Do the stars twinkle at night where you live? While that makes for a pretty light show, astronomers do not like twinkling stars. The twinkling is caused by currents of air in the atmosphere, which make the image of a star dance around a tiny bit, causing the twinkling effect. If you've ever tried to take a picture of a dancer in motion, you know that it can be nearly impossible to avoid some blurring due to the dancer's movement. So it is with the stars and other objects in the night sky - you can't take clear pictures of them, or even see them clearly, if they are dancing around. And, since the telescope magnifies the image, this movement is also magnified, making the problem even worse.
The stars don't twinkle much in Hidalgo County; the air tends to be very stable, and the stars are often hard, steady pinpoints of light. One reason for this is Hidalgo County's location. The "jet stream" that you hear about on the nightly weather report seldom dips this far south, so it doesn't stir up the upper atmosphere; this leaves it smooth and undisturbed for starlight to travel through.
So, if you're looking for a clear, brilliant view of the night sky, Hidalgo County is the perfect place to visit.
Photo courtesy Alan Morton, Rexburg, Idaho, from the Bunker Ranch Observatory
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