At Black Canyon of the Gunnison National Park, we are lucky to have dedicated local astronomers, powerful telescopes, and pristinely dark skies.
A naturally dark sky with no light pollution contains a faint magnitude 22 star in every tiny square of your field of view. On June 3rd of this year, we recorded a sky darkness reading of 21.8, just .2 points shy of this level. But there is a limit to earthly darkness. What natural night-lights impact our near-perfect sky?
Light itself can be described in two ways: as discrete packets of energy called photons, and as waves of varying frequencies. Stars create and expel light of all energy levels and frequencies to the unknown edges of our universe.
Not all of that light reaches Earth’s surface. Distant starlight scatters as it collides with atmospheric particles, adding a nearly invisible blue hue to the night sky. Much of the high-energy light, like x-rays and gamma rays, is filtered out in the stratospheric ozone layer.
Faint starlight also competes with the sun’s rays even at night. Sunlight almost continuously excites oxygen particles in the upper atmosphere, producing a subtle green tinge we can capture in long exposure photographs. Sunlight also reflects off more than the moon and planets- it highlights a disk of comet dust, the largest visible structure in our solar system, creating a phenomenon called zodiacal light. Since the disk is aligned with the zodiac, and the zodiac’s angle is most severe at each equinox, this is a good time of year to search for the light just before dawn.
With all this production and elimination of light, you may feel discouraged about what wonders we miss in our dark skies. But our bare eye can still detect light from the Andromeda galaxy over 2.5 million light years away, which left that system before the first humans left Africa. Cataract surgeries can also allow our eyes to perceive ultra-violet light, which may give stars a brighter, bluer brilliance. Regardless of what light can be seen, simply trying to perceive every visible star in a 21.8 sky is an incalculable, unforgettable experience. Places like Black Canyon work to protect dark skies to provide this experience for everyone.
Western Slope Skies is produced by members of the Black Canyon Astronomical Society. This episode was written by Park Ranger Molly Pittman of Black Canyon of the Gunnison National Park.