Night Sky Survey

Completing a Successful Night Sky Survey

A thorough Night Sky Survey is essential to a successful application to the International Dark Sky Places program.

There are a variety of ways to approach it and improve upon it.

These include:

  1. The Sky Quality Meter Survey
  2. The Bortle Scale Interpretation
  3. The Photographic Evidence

 

Sky Quality Meter Survey

This is perhaps one of the easiest ways to achieve quantities measurements of the darkness of your location’s dark skies. First, you will need a Unihedron Sky Quality Meter. This is available for $119.99 USA dollars plus shipping and handling from Unihedron’s website.

It is simple to use and effective at measuring sky brightness at zenith. Simply hold the device above your head, pointing the photometer at zenith, and click the button. The screen will then display the magnitude of the sky brightness at that point; the higher the number, the darker the sky. Take three to five measurements per location and average the results. Never take a measurement directly underneath a light source or anything that might block the clear sky. Always take measurements with clear open sky, cloudless, to prevent any sky glow measurements that will deter the accuracy of the device. Also, always take measurements on clear, moonless (New Moon) nights. Measurements taken during Full Moon and while the Moon is visible will not reflect the natural darkness of your location.

Using this device a “grid” of the locations may be made. It is essential to include areas that will be the darkest and the brightest to achieve a comprehensive survey of the location.

 SQMmap

In the map above a suggested method is shown for creating a survey. Include measurements of the borders, active areas, and presumed darkest areas of the park. This data can then be organized into a map showing approximate location of measurements and a table. An example table is also shown below. The numbers used by the SQM represents the amount of light coming into the sensor on the top. The higher the number, the darker the sky above. The guidelines discuss how dark the sky must be to achieve each tier designation; either Gold, Silver, or Bronze.

SQM Average

Location

Reserve Section (for Reserves only)

Notes

21.9

Border

Buffer Zone

 

21.0

Active Area

Critical Buffer

Brightest Area

22.7

Darkest

Core Zone

Darkest Area


View a Chinese translation of these instructions: 點擊此處下載指南:  夜空調查說明 (Night Sky Survey Instructions)
Translation courtesy of IDA Beijing / Starry Sky Project of China

Bortle Scale Interpretation

The Bortle Scale works to estimate sky brightness and interpret how light pollution is affecting your view of night sky phenomenon. The easiest way to interpret the Bortle Scale is an easy flow chart. Follow the questions to reveal what Bortle Class your skies fall under. This may need to be done at different locations in the location if sky brightness varies, for instance, you may have a Bortle Class between 3 and 4. The lower the number is, the better sky quality.

This method is less quantitative than the Sky Quality Measurement. An application using only this method to document Sky Quality is not as strong as an application using the SQM method or using two or more methods.

Steve Owens, International Dark Sky Places Committee member, is credited with the flow char below. Learn more about it on his Dark Sky Diary.

 

Have little to no experience stargazing? No problem. Visit Sky and Telescope's article "How to Start Right in Astronomy" to learn more about picking up amateur astronomy skills.

Also see Sky & Telescope's easy guides "Getting Started in Astronomy" for the northern and southern hemispheres for star maps and other information on how to proceed.

We also recommend looking for advice and help from local amateur astronomers. Find local astronomy clubs near you hosted by NASA's Night Sky Network (USA only).

View a Chinese translation of these instructions: 點擊此處下載指南:  Bortle 暗天空的等级 (Bortle Dark Sky Level)
Translation courtesy of IDA Beijing / Starry Sky Project of China

 

Photographic Evidence

Like the Bortle Scale method this method is less quantitative than the Sky Quality Measurement. An application using only this method to document Sky Quality is not as strong as an application using the SQM method or using two or more methods.

However, it can be very useful to support the Bortle Scale method and document specific nighttime phenomenon. For example, imaging the Milky Way, the Zodiacal light, and the Gegenschein make for a much stronger use of the Bortle Scale.

When including images also include a breakdown of the camera details used to take it, i.e. exposure time, focal length, ISO, etc… See the example below.

 
Photographer: Ameé Hennig
Location: Cerro Pachón, near SOAR Telescope in Chile (GPS location if available)
Phenomenon Shown: Milky Way, Large Magellanic Cloud
Camera: NIKON D3000
Exposure: 17.5 sec (1/0)
Aperture: f/3.5
Focal Length: 18 mm
ISO Speed: 1600
Special Editing: None
 

This method, along with others, have proven successful. If you have additional questions, please contact the Program Manager at This email address is being protected from spambots. You need JavaScript enabled to view it.