Light pollution can steal stars from night sky

Greetings, stargazers.

I recently received some new lights for the Old Fort Lewis campus, where the observatory is. These new lights are to replace the current street/security lights, and once they are installed, they should improve the view there considerably. This is a great excuse to talk a bit about the dark skies in the Four Corners region.

The new lights use LED technology, so are more energy efficient and should have a much longer life expectancy. Plus, a La Plata Electric Association rebate for using LEDs makes them much more affordable. As with other new street lights installed in La Plata County, the new lights are full cutoff, directing the light downward, not to the side or up. The old-style “barn light” they are replacing sprayed light down, to the side and even a significant fraction up into the air.

Perhaps the most significant new feature of these lights is that most won’t stay on all night. Several will get motion detectors, and others will have timers to be on for a while at dusk and dawn, but be off in the middle of the night. For lights installed for “security” (or is it insecurity?), the evidence is mixed as to the actual effectiveness.

The picture of the Earth at night (see the link) is quite beautiful, easily showing all the major cities. However, any light you can see from space and shining up from the ground is just wasted energy. And those bright points indicate all the places where it is hard to see the night sky.

Beside interfering with your night vision, the reason lights make it hard to view the stars is that the atmosphere actually reflects some of the light back to the ground. When the air is lit up with unwanted light, it washes out the things you are trying to see. If you are out in the county, you can look back and see a small dome of light in the sky over Durango, and a much larger dome over Farmington. The farther away from any of these light domes you can get, the better your view of the night sky will be.

The International Dark-Sky Association website (see the link) has lots of useful information about nighttime lighting and about preserving dark skies.

If you are expecting company, certainly leave the front porch light on, but please turn it off when you go to bed – your neighbor might be trying to enjoy the Milky Way.

This month

Mancos State Park and Mancos Public Library are planning a star party at the state park Saturday. There should be quite a few telescopes for public viewing. Although sunset is as late as it ever gets now, as soon as it gets dark, the summer Milky Way is rising, with its scores of open and globular clusters.

The next Durango Nature Studies new-moon event will be July 8. Join the Four Corners Stargazers for more information about these events and other local star parties.

hakes_c@fortlewis.edu. Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.

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