Before	After

In this presentation by Doug Kniffen, I learned that these photographic “enhancement” filters are fairly effective at blocking light the color emitted by sodium (and thus emitted in sodium lights). While not designed for telescopes, when employed for off label uses, these filters allow astroimagers to take aesthetically pleasing pictures from sites that otherwise can’t support deep sky photography.

If you look closely at the images above, you’ll notice there are actually more stars near the horizon in the After image than in the before. Specifically, look above and to the right of the house in the center. There are two stars in the image on the right that just aren’t in the image on the left.

From what Kniffen said, you can’t get these filters in standard – screw onto your eyepiece or insert into your filter wheel – sizes, but they do exist in many camera size, perfect for the piggy backed camera. I did a bit of research, and found them here at very reasonable prices (mind you, in grad school I managed to destroy a $1500 filter, so, well… I have weird scales for these things). Now that our house has roof top access (we are resurrecting a widows walk), I may have to get one and try doing some city-based astrophotography. It has been a long time since by happy little SLR (yes, film) camera saw starlight, and a new filter just might be the kick in the butt I need to get going again.

White light, by definition, is a combination of all the different colors of the spectrum. White LEDs, aren’t a perfectly flat distribution of energy as a function of color. They have a very distinct peak in the blue. It’s this peak that causes problems.

Different colors of light reflect and scatter in different ways. In general, red light can make it though a cloud of fog or dust, while blue light is scattered hither and yon. This is actually how we end up with blue and red nebulae. The red light in red nebula comes directly from background stars and is transmitted through the cloud to our eyes, telescope, or binoculars. Blue nebulae are the result of looking at a cloud of gas that has star light hitting it from the side, top, or bottom. The blue light that was scattered comes out in all directions, and is thus visible indirectly. You can demonstrate this by taking an empty 2 liter, filling it with water and a dash of dried milk powder, and then shinning a low power white flash light through the water from different angles.

Today, our low-pressure sodium light bulbs cast an orange glow on everything, but that orange glow tends not to back scatter too badly. The light passes through dusty air to illuminate parking lots and walk ways, and doesn’t reflect off of typical asphalt walkways with too much enthusiasm. Blue light, with its shorter wavelength and higher energy, won’t be so polite, and will eagerly scatter off of anything and everything: dust, fog, the ground, you, the grass, etc. Scattered light can defeat careful attempts to prevent light pollution that rely on downward facing lights.

When people try and illuminate objects, their goal should be to have the photons travel from the light source to the object where they are reflected only in directions where onlookers may be looking from. In theory, onlookers should not include people in planes or in space. In this perfect ideal situation, night time satellite images would show a darkened planet Earth instead of the current trace of major cities and sprawling suburbs (and the occasional shrimp fleet). Because we like to illuminate parking lots and walkways (and the ground in general), this perfect dream will never happen, but at least the red light is unenthusiastic about going to outer space.

If we replace our current low-pressure sodium lights with white LEDs, we will save energy. Cities and individuals will save time (and money) by not having to replace bulbs as often. As humans, we also psychologically will be happier with the white light. Win. Win. Win. Except for the scattering. And there is another problem – It’s easy to make these things BRIGHT. Car dealerships will be able to afford to have their lots as bright as the noonday sun at midnight. High Schools won’t sweat the costs of lighting up their football fields, and marching bands won’t be restricted to practicing in daylight. Everything can be made bright bright bright for low low costs.

And bright at night is bad. You can find links to papers discussing effects on human health, animals, plants, and nighttime resources like stars on the IDA website.
So, these white light LEDs are leaving me conflicted. They save power, effort, and make things look better at night. But they ruin the night. They steal the stars and have the potential to harm many critters that matter.

I never thought I’d be upset to see a break through in energy saving light sources.

While I was a graduate student at the University of Texas in Austin I watched the Ring Nebula (M57) disappear. When I first arrived in 1996, this former stellar atmosphere was clearly visible in binoculars from the roof of the building I worked in (RLM). In 2000 I could no longer see it, but some of my more owl-eyed students could see it faintly contrasting against the background glow of too many city lights. When I graduated in 2002, it was just gone. No pair of 10×50 binoculars was going to find it. According to the Greater Austin Chamber of Commerce the city grew from 846,227 people in 1990 to 1,452,529 people in 2005. With that growth came lights, and with those lights came star consuming light pollution. As the world population grows and becomes progressively more industrialized, our entire planet is losing its ability to see faint stars and galaxies in the night skies.

In an attempt to raise awareness about this problem and document what is going on, the excellent education team at the GLOBE is getting ready to run their the GLOBE at Night program. Last year, over 18,000 people from 96 countries from all continents except Antarctica participated, documenting how light pollution effects the skies everywhere.
I strongly encourage everyone to participate in this project for one simple reason: So you can compare what you see with an image of what you would see if your skies were perfect.

One of my most eye opening experiences as a young astronomy student came while sitting on a rock at the foot of a glacier in the Northern Caucus Mountains. It was the middle of the night. Our camp fire was down to low embers behind me, and looking away from camp the mountains loomed darkly against a star-bright horizon. As I sat facing the ecliptic, I struggled to find the familiar signs of the zodiac among the million points of light. As I searched for familiar patterns I kept getting distracted by satellites. There was simply too much in the sky and I was lost.

I’ve seen dark skies since then. Observing at McDonald Observatory I learned that in dark locations clouds are blobs of blackness – the great nothing of the Neverending Story – against a starry backdrop. I also learned that a few 100 people who don’t turn off their lights can create a yellow patch on another wise blue-black horizon. The major observatories of the world are each trying to save their skies from encroaching city lights. Recently, Kitt Peak Observatory released a spectacular image of a very faint face on spiral galaxy (IC 342, above right, credit: T.A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN, and NOAO/AURA/NSF) to showcase just what their telescopes are capable of thanks to progressive city ordinances curbing light pollution. As the nearby city of Tucson has grown, light pollution at Kitt Peak has grown, but very slowly. Today, it appears that additional growth may be possible without degrading Kitt Peak’s skies.

Not all observatories are lucky enough to have nearby cities and townships work so hard to curb pollution. For instance, consider the misfortunes of California’s Mt Wilson Observatory with the great Palomar telescope. Built on the hills outside Los Angeles, this telescope has watched the city grow and the sky light up with the light from several million people. It doesn’t have to be this way. To protect our skies only 4 simple steps are necessary: Don’t use more light than is necessary for a given task, point lights down from above not up from below, shield light so it doesn’t scatter upward, and use low-pressure sodium lamps as much as possible. These 4 steps will save our skies, and also save on electricity (which saves our entire planet).

With the lose of our skies, we aren’t just losing our ability to see stars, we’re also effecting out health and nature. Hatchling sea turtles aren’t finding the sea. Rodents that eat by the cover of darkness are more easily eaten. Lots of bad stuff that is outlined effectively on The International Dark Sky Association’s (IDA) resources page.

So, go out and lookup with the GLOBE, and then go in and find out how you can help IDA protect what is left of out skies.