Friday, May 27, 2016

Skyglow surveys with an SQM and the Loss of the Night app

I was just looking through the Loss of the Night app data, and noticed that a project participant used the app and an SQM to do a skyglow survey of the island of Öland, Sweden:

Öland skyglow survey is licensed under a
Creative Commons Attribution 4.0 International License.
Link to the interactive map at

I reached out to Jörgen Tannerstedt, in order to get the story behind the map. Here's what he told me:

The story behind the measurements is that we last year started a project called "Dark sky Öland" in the local astronomical society on the Island of Öland, Grönhögens Astronomiska Förening (GAF). We are a rather small astronomical society, with fewer than 30 members, but we like our island and the darkness that we've got, and we want to protect it for the future and make others aware of it. There are also some plans/thoughts of applying to IDA and try to make some part of the island a dark sky park or reserve. The southern part of Öland is a world heritage site, and perhaps one could try to make that to a light protected area as well.

"Night over the lake" is copyright Jörgen Tannerstedt.
Used with permission.

As a first step in this project we bought a SQM-LU meter to start measuring the sky brightness all over the island. I guess I´m the most active member in our society, so I got the meter in my hands and have brought it with me most of the time when I´m out shooting. I take mostly astroscape images from the island, some of them can be seen here.
I recently got myself a telescope, and had it just set up before we lost the dark nights here up in the north. So now we just want the summer to end and get the darkness back :P August 10th is the first night with astronomical darkness again after the summer break for the island.
"Stargazing" is copyright Jörgen Tannerstedt.
Used with permission.

So far I have measured over a hundred different locations on the island, several locations multiple times and I will continue doing this during the autumn. There are still several good locations left, and I also want to measure in and close to villages to see how much influence they have, and how much light is spread to the nearby surrounding.

It´s rather recent that I discovered the Loss of the Night app, and it has made things so much easier for documenting the measurements. I really like the ease of use, and that the observations are automatically GPS tagged.

Our measurements will be used to evaluate how good and dark the sky is, and serve as a "before" value to see if it gets better or worse in the future. For example, the area near the bridge to the mainland is under heavy construction, and a lot of new houses are being built with road and street lights etc.

The measurements are also going to be used in a guidebook that another member, Lars Magnusson, is working on. In the guidebook, we will include a lot of good locations for astronomers that want to come to the island and experience our dark skies. We will also include information about the different locations, availability, public toilets, photos etc. Hopefully will we have a first version ready this autumn

When shooting from the southern cape of the island, the camera can easily pick up light from cities the other side of the sea, like Gdansk/Gdynia area in Poland. For example, in this picture the light pollution out to the right under the central parts of the Milky Way are from Gdansk/Gdynia, about 250 km away.

If anyone would like to come and visit the island we have the astronomical darkness back again august 10th, and then later in the beginning of september with the new moon, we have our yearly star party "Sagittarius". It's a rater small party with some spontaneous lectures during the daytime and most often a geological excursion and then stargazing all night :D It's always nice to meet others with the same interest. During summertime, there are a lot of tourists here, from Germany, the Netherlands, and Belgium. We've even got a hotel here that is named "Drei Jahreszeiten*". The winter is not that fun, and pretty windy here, so I understand they skipped that season :D But so far I haven't heard anything about any astrotourists.

* "Three seasons"

My hat goes off to Jörgen and the other members of GAF for documenting, sharing, and especially working to preserve your natural starry skies on the island of Öland! Hopefully your book will lead to a few extra astrotourists to fill up the Drei Jahreszeiten hotel!

While it's nowhere near as organized as what GAF is doing, I have taken advantage of my trips to the state of Mecklenburg-Vorpommern in Germany with some similar goals in mind. I also hope this area will someday be home to one or more recognized International Dark Sky Places, where the communities have recognized the value of the night sky as a natural resource, and agreed to work together to protect it. Here's my map:

Skyglow survey MVP is licensed under a
Creative Commons Attribution 4.0 International License.
Link to the interactive map at

If you have an SQM, this method of surveying is a wonderful way to contribute to environmental monitoring of Earth's night! The data are shared with everyone around the world, and they contribute to a permanent archive of the skyglow conditions at the site. If you are planning on founding an International Dark Sky Park or Reserve, this allows you to document the conditions at your site transparently, and future visitors will be able to verify your results and contribute to monitoring changes in the sky condition.

Please note that the best way to do an SQM measurement is to average the result of 4 measurements with your body oriented in the four different compass directions. This is the recommendation from the Loss of the Night Network, and we have found that it considerably reduces the size of the uncertainty compared to taking just a single measurement. Here is the full text of the recommendation from the LoNNe report:

Recommendation #1: When making observations with a handheld SQM-L, you should average the result of four observations, rotating your body after each observation to a different compass direction. If the SQM-L is being affected by stray light, this may minimize or reveal the effect. If the four observations are not self-consistent (maximum range about 0.2 magSQM/arcsec2), then it is probably not a good location, and the data should not be recorded. This technique has been suggested by Andreas Hänel in the past, and we advise all handheld SQM-L users to adopt it.

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