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Dark Sky Map

Dark Sky: Where Are You? [Astrophotography]

Milky Way
Milky Way (I didn’t take this photo)

The hunt for a dark sky was once imaginary. Before Lewis Howard Latimer and Thomas Alva Edison dropped the mic on the light bulb, it was common place to look up on a clear night and see the Milky Way. Their invention created a new term, light pollution and it’s the only pollution that grows unchecked year over year. Oxford defines it as ” brightening of the night sky caused by street lights and other man-made sources, which has a disruptive effect on natural cycles and inhibits the observation of stars and planets.” Let’s dig deeper to understand light pollution further.

Dark Sky Measurements

How is light pollution measured? Astronomers and Astrophotographers use the Bortle Scale. It is a numeric scale broken into 9 levels and was developed by John E. Bortle in 2001. Below is a visual representation of the scale.

Light Pollution Graphic visualization of the Bortle Scale.

So under which sky do you want to be? I choose the Bortle Class 1 sky, which for me is a flight or 2 day drive away. Below is a dark sky map of my region and I’m in a Bortle class 5 zone.

Dark Sky Map
Dark Sky Map

Where to Look

If you’re interested in traveling to a dark site, one way is to research different astronomy clubs. Several host large star parties at various dark locations throughout the year. In addition, jumping over to Dark Site Finder to search an area near you. Only thing left is to travel to the area.

No Dark Sky, Other options

About that travel requirement, what other options are available? In addition to traveling, there are several other options available.

  1. Day time observing only (Solar Observing with a solar filter of course)
  2. Move
  3. Add filters to your astrophotography

Astronomy and Astrophotography have found ways around the light pollution problem. Utilizing filters that block the unwanted light are becoming a must in the field. The following are the filters available for your telescope or camera:

  • Solar (blocks 99% of the Sun’s light)
  • Light Pollution Filters or Sky Glow Filters
  • Neutral Density (for Moon Observing)
  • Narrowband Filters (for deep sky astrophotography).
Orion Skyglow Imaging Filter

Why Filters Work

Imagine going to the grocery store for a handful of items yet having to leave with everything in the store or nothing. I’m never shopping there again! Astrophotography is similar. All night sky objects reflect or product light in specific wavelengths. Consequently, those wavelenghts of light are unique and can be separated from the glow of the street lights in your neighborhood or city.

Between half and full Moon presents a different problem. It’s bright enough in these unique wavelenths to make deep sky astrophotography difficult. I photograph the Moon or planets then swith to deep sky later in the month. Bright objects like Andromeda Galaxy and Orion Nebula are options during this time. And bright objects are key. This is why I choose those objects. I also choose some of them because they are far enough away from the Moon light to photograph.

There are many different brands of filters on the market. Based on your experience, one type may work better than others. Try them out till you achieve what satisfies you.


Maximizing your capture or viewing time is important. Therefore having your filters organized is a must. It is equally important to know what object(s) and position(s) you’re going to view. Knowing this information will help you prepare for the Moon’s glow or the opposite with maximum darkness for that area.

I use Stellarium to prepare and I also keep my filters in a small portable case. Just for those times I miss something in my preparation. In your journey, take lots of pictures. Clear skies!

Kevin Francis

Kevin Francis is a Mechanical Engineer by day, amateur Astrophotographer by night who is taking his Google Pixel smartphone camera to new limits.