Light Pollution

Image Credit: David Lorenz, Attribution, via Wikimedia Commons

Amateur astronomers face two overwhelming obstacles when trying to view the wonders of the night sky. The first is the weather. Well, there is little we can do about that – clouds roll in and the weather is the weather. The second, is light pollution. We are losing the night sky to artificial light at an ever-increasing rate. It not only disrupts our view, but it also has a negative impact on the natural patterns of wildlife, ecosystems, human health, and sleep. In addition, wasted light costs $2.2 billion annually.

When we look down at the Earth from space, it seems that light is everywhere. For a closer look, you can zoom in on the light pollution in any part of the world using this online light pollution map.

Not all light pollution is the same. There are five general categories.

  1. Over-illumination, where lights are on, but not needed.
  2. Glare, where light reflects off the ground or buildings.
  3. Light clutter, where lights are poorly placed.
  4. Sky glow, where light escapes from outdoor lighting and reflects down from the atmosphere.
  5. Light trespass, where light intrudes on another’s property.

The International Dark Sky Association (DarkSky.org) provides many resources and guides to help you identify sources of light pollution and ways of combating it. In particular, make sure light is useful, targeted, no brighter than necessary, used only when needed, and bathed in warmer colors. There are several dark sky observing locations you might try if the local light pollution gets too much for you.

The degree of light pollution is often assessed qualitatively using the Bortle scale, which ranges from 9 (very light polluted) down to 1 (extreme dark sky). Light pollution can also be more quantitatively measured using a Sky Quality Meter (SQM). Individuals can participate in the Globe at Night program and submit their own measurement of light pollution. Several online maps can be found showing the level of light pollution. Those using telescopes might find that filters are very useful in blocking or minimizing the effect of light pollution. There are some local ordinances that might help (maybe).

Light pollution is not the only problem. Satellites are now covering the night sky applying streaks across our images. To make matters worse, companies are now starting to offer sunlight on demand.

If you want to learn more about this problem, see the many more resources at the bottom.

International Dark-Sky Association / DarkSky.org

The International Dark-Sky Association/DarkSky.org (IDA) provides an overview of light pollution and its impact on us and our environment. They suggest “five principles for responsible outdoor lighting” that you should follow when installing outdoor lighting. You can also see their “Dark Sky Friendly Home Lighting Program” for more advice and guidance. If this is too much, the IDA has a simpler set of guidelines we can all use See below.

Bortle Scale

In 2001, amateur astronomer John Bortle develop a scale with which to classify the degree of light pollution affecting the night sky. The folks at the Skyglow project have a nice chart showing the Bortle scale. If you want to approximate the Bortle classification for your neighborhood, Steve Owens has a flow chart you can follow.

Botrle Scale. Image Credit: ESO/P. Horálek, M. Wallner, CC BY 4.0 https://creativecommons.org/licenses/by/4.0, via Wikimedia Commons

Sky Quality Meter (SQM)

The degree of light pollution (actually the general seeing conditions) can be measured in a more quantitative way using a Sky Quality Meter (SQM) from Unihedron. It will provide a measurement of the night sky in magnitude per arc second squared. There are two models available – one with a wide view angle (SQM) and another with a lens producing a narrow view angle (SQM-L).

Trevor Jones (AstroBackyard) has an approximate relation between your SQM readings and the Bortle Scale.

  • Close to 22 -> Bortle 1
  • Just above 21 1/2 -> Bortle 2
  • Just below 21 1/2 -> Bortle 3
  • 20 1/2 to 21 1/4 -> Bortle 4
  • Just above 19 to 20 1/4 -> Bortle 5
  • 18 1/2 to just above 19 -> Bortle 6
  • 18 to 18 1/2 -> Bortle 7
  • Below 18 -> Bortle 8 & 9

Globe At Night

Globe at Night is an international program that allows individuals to submit either qualitative or quantitative (SQM) measurements of light pollution in their night sky. Here is their description of the program.

The Globe at Night program is an international citizen-science campaign to raise public awareness of the impact of light pollution by inviting citizen-scientists to measure their night sky brightness and submit their observations from a computer or smart phone. Light pollution threatens not only our “right to starlight”, but can affect energy consumption, wildlife and health. More than 200,000 measurements have been contributed from people in 180 countries over the last 14 years, making Globe at Night the most successful light pollution awareness campaign to date!

Dark Sky Maps

There are several online maps showing measurements of light pollution throughout the world.

Dark Sky Observing Sites

It is difficult to go back and remove or remedy existing light, so often the only solution is the get away from the city and find a dark sky location. The good news is, for those of us living in North Carolina, that there are some options. FAS manages a small observation platform for its members just north of Pilot Mountain. It is a half hour to 45-minute drive from the Winston-Salem area and provides a reasonable dark sky. FAS has also compiled a list of dark sky observation sites that club members have used in the past. If you have another site or additional information, please let us know.

Local Dark Sky Observing Sites
Dark Sky Observing Notes

Local Exterior Lighting Ordinance

Winston-Salem/Forsyth County does have an exterior lighting ordinance. It, however, only addresses lighting for businesses and sports venues. Source: UDO Clear Code (Section 6-6). It does not address residential or street lighting. For issues with this type of lighting, you might contact the City-County Planning Board (Kelly Bennett) – although we are not sure where this suggestion came from.

Exterior Light OrdinanceDownload

Filters

When using a telescope, and particularly when imaging objects in the night sky, filters will go a long way to reducing the image of light pollution. Overall three types are available.

  • UV/IR Cut Filters (aka Luminance Filters) cut out non-visible (UV and IR) light and allow only visible light through.
  • Broadband Filters cut out the effects of light pollution. These can be used for most deep-sky objects. Several members have the L-Pro or the newer L-Quad Enhanced filter from Optolong.
  • Dual-Narrowband Filters captured wavelengths. Hα (656nm), OIII (500nm), and possibly SII (672nm), from emission (and planetary) nebulae. Several members have the L-eNhance (10nm/24nm), L-Para (10nm), L-eXtreme (7nm), or L-Ultimate (3nm) filters with different bandwidths from Optolong.

Satellites

In addition to the traditional light pollution, satellites are now streaking across our night sky more than ever. As we look up we can see more and more Starlink and other satellites finding their way into our field of view.

The Night Sky from Stellarium (showing several Srarlink satellites)

Sunlight on Demand

There is a new type of light pollution creeping into our night skies. This might make the entire issue much more problematic with a proposal to offer sunlight after dark using satellites with mirrors. The FCC just gave its approval for Reflect Orbital to launch and test their first satellite, Earendil-1, which will reflect light down over a three mile wide area. According to EarthSky, Reflect Orbit is planning on operating over 50,000 satellites by 2035.

More Resources

Resources (Articles)

Resources (Videos)

For more on light pollution and dark skies, see our various posts and articles.

Light Pollution News and Posts