by Rex Parker, Director
Dark Skies, Our Eyes, and Outdoor Lighting.
Nearly three-fourths of all Americans reside under skies where the Milky Way is not visible. It’s natural as we age to lose some night sky acuity, as our upcoming guest lecturer, author James Chen, will discuss on November 14 (see the section by Program Chair Ira Polans in this issue). But in addition to aging eyes, worsening light pollution translates to further loss of night vision especially in NJ and the northeast. Among several aspects to this issue, one that I want to bring to your attention is skyglow, the increased sky brightness arising from light scattered by aerosols and molecules in the atmosphere.
Initial optimism for replacing outdoor lighting fixtures with energy efficient solid state LED luminaires, originally thought to reduce light pollution, has recently turned to concern within the astronomy community. As installation of the new LED technology expands around the country, it has become apparent that the relatively blue-rich LED spectrum actually worsens visual skyglow. This unfortunately diminishes the ability of the dark-adapted eye to see stars and the Milky Way, and worsens the contrast of faint deep sky objects in telescopes. Compared to the yellow-shifted emission spectra of the historically most used lighting fixtures, high or low pressure sodium vapor, the adverse effects of blue-rich LEDs are an ominous new threat to our remaining natural night skies.
This emerging well-intentioned effort to replace older outdoor lighting fixtures with newer LED lighting is going to make our astronomical lives more difficult because of the shift in light source spectrum. Most of the discussion about these light sources concerns their favorable electricity usage and profile for normal light adapted (photopic) vision, which is physiologically distinct from night (scotopic) vision. Scotopic vision is dependent on the eye retina’s rod cells which are sensitive to shorter wavelengths of light (blue to green) and insensitive to longer wavelengths (red). This is why light sources richer in short wavelengths stimulate our dark adapted vision and make artificial sky luminance we perceive as skyglow. A recent report by US Naval Observatory astronomer Christian Luginbuhl describes this situation in depth (Journal of Quantitative Spectroscopy & Radiative Transfer 2014, 139: 21–26.) Another good discussion of the topic including several spectrum examples of the various lighting types can found here: http://www.flagstaffdarkskies.org/for-wonks/lamp-spectrum-light-pollution/.
One solution to the problem is to promote a change to yellow/amber-filtered LED sources, which are becoming available from manufacturers. I urge AAAP members to become more informed by reading up on these complex issues and spreading the message to use amber filtered LEDs whenever possible, while there is still a chance to make widespread changes.
Skynet Update. Taking other steps to mitigate skyglow and loss of night vision, to date 26 members have requested Skynet accounts, and 9 of us have taken images with the Skynet robotic telescope network. Our arrangement with the University of North Carolina, Chapel Hill, Physics and Astronomy Dept, provides remote astrophotography access using state of the art telescopes, mounts, and CCD cameras and software. The instruments are located at observatories spanning the globe. This is an exclusive benefit of AAAP membership, as we seek to gauge interest among members for deeper learning about astro-imaging technologies and approaches. If you’re interested but haven’t yet taken the plunge, send me an e-mail note and I’ll provide you with an account to log-in to the system.
Mark Your Calendar for Next Year’s StarQuest. At last month’s meeting we voted to continue the Jersey StarQuest tradition next year. We’ve reserved Oct 5-6, 2018 at Hope Center in north Jersey where the effects of light pollution are less than around Princeton. The deep sky observing conditions at Starquest-2017 last month were among the best we’ve had in New Jersey, reminding us why we pursue such a challenging avocation as seeing faint, distant galaxies and nebulae with our own equipment through our own eyes!