NPS Photo by Sean Dupre Gateway to the StarsIf you haven't already noticed, Gila Cliff Dwellings National Monument is in the middle of nowhere! The 558,000 acre Gila National Wilderness and 3.3 million acre Gila National Forest envelop the monument and protect the entire area from development. So the nearest source of light pollution, Silver City, NM, is over 40 miles away on the other side of two mountain ranges. This makes an exceptional environment for viewing the cosmic cabaret that plays out every night.How dark is it?There are several ways to measure the quality of a night sky, or the lack of light pollution in a given area. The most common unit of measurement used by astronomers is known as "magnitudes per squared arc second (mag/arc-sec2)." This is a measurement of brightness (magnitude) across an area (squared arc second).Magnitudes are measured on an inverse scale; so the brightest objects in the sky have the smallest magnitude. The sun, for example, is a magnitude -27. Venus measures around -5 and Saturn is a 0. Stars and other deep-space objects have positive values which get larger the dimmer the objects get. The night sky is divided into 360 degrees around the earth. Each degree is divided into 60 minutes, and each of those is divided again into 60 seconds, to help astronomers pinpoint and share specific areas in the sky. A square arc second is an area of the sky that measure 1 arc second by 1 arc second. A sky quality measurement is a statement about the brightness of the sky stretched out over the space of a square arc second. The best night sky (i.e. the middle of the Pacific Ocean) is measured at 22 mag/arc-sec2. Anything beyond that is considered "unphysical" by the International Dark-Sky Association. The skies over Gila Cliff Dwellings National Monument is consistently measured at 21.8 mag/arc-sec2 or greater. Bortle ScaleAnother effective measurement method, though slightly subjective, is the Bortle Scale. Developed by amateur astronomer John E. Bortle, this method assigns a class number from 1 to 9 based on whether or not certain known astronomical objects can be seen from a given area.From the Gila Cliff Dwellings, the Milky Way galaxy can be seen most nights, sometimes even while the moon is out, and the detailed structure of the galactic center is evident in the summer sky. In fact, on some clear moonless nights, you can even see your shadow from the Milky Way's light! These factors make the Gila's skies a Bortle Class 1 or 2, which is some of the best night skies you can find in the continental United States. 
NPS Photo/Jonah Snead The Stars of the ShowThanks to the lack of light pollution and some 200 cloudless nights experienced throughout the year, Gila Cliff Dwellings sets a phenomenal stage for countless cosmic shows for every season. The last few years have brought on planetary alignments, comets and eclipses, but some shows return each year like clockwork. During its path around the sun the earth encounters several congested sections, usually the remnants of comets past, that lead to stunning meteor showers down here on land.Some of the most spectacular meteor shows of the year include:
Note: Due to annual monsoon rains, summer skies are usually clouded over; thus summer is not a good time of year for star gazing in the Gila. 
NPS Photo by Zoltan Kollath |
Last updated: November 20, 2024