These filters work by suppressing the wavelengths of sunshine emitted by artifical sources to permit mild from astronomical objects by way of.
This beautiful picture of the Orion Nebula (M42) was captured below closely light-polluted skies, because of assistance from a light-pollution filter. Credit score: Stephen Rahn
How do mild air pollution filters work? Do they really assist?
Kyle Norris
Peoria, Arizona
Gentle air pollution discount (LPR) filters work as a result of many outside lighting sources don’t shine evenly throughout the seen spectrum. As a substitute, they emit radiation at just a few distinct wavelengths. As an illustration, a high-pressure sodium streetlight radiates principally in yellow wavelengths. LPR filters suppress these and related wavelengths whereas permitting others by way of.
LPR filters don’t scale back all types of mild air pollution, regardless of their identify. They do little to cut back the affect of automotive headlights, lights directed onto buildings, and different fixtures that (sadly for astronomers) emit all seen wavelengths.
One other widespread fallacy is that these filters make sky objects look brighter. Filters solely subtract mild, dimming every little thing. Within the course of, nonetheless, the background sky and discipline stars darken greater than the goal. This boosts the distinction, making celestial objects simpler to identify.
Some amateurs consider these filters dim the view a lot that they’ll’t use them with small telescopes. That’s additionally not true. Any telescope can profit from these filters.
Underneath city and suburban skies, LPR filters carry out greatest on vivid nebulae. Whereas a filtered view seldom reveals extra element than an unfiltered one, or reveals an in any other case invisible goal, LPR filters enhance the visible aesthetics by darkening the background sky. And even from a darkish web site the place there’s no mild air pollution, nebulae are inclined to look a bit higher.
When you reside below a dome of sunshine air pollution, take into account including an LPR filter to your tools arsenal. When you begin utilizing filters, you’ll be amazed at what you’ve been lacking. It’s the identical nice expertise as placing in your “shades” on a sunny day.
Michael E. Bakich
Affiliate Editor
This query and reply initially appeared within the July 2012 concern.
