Saturday, November 2, 2013

Looking for stars in Berlin

Last week we hosted the first ever international conference on artificial light at night, ALAN 2013! After two evening events of the conference, I took advantage of being out on a night with clear skies to use the Loss of the Night app in three places. I've labelled their approximate locations on this map of Berlin at Night from the Suomi-NPP VIIRS image:

The first location, "Dahlem" is in a suburb at the edge of Berlin. The second, "Spreebogen" is an unlit park across the river from the brightly lit main train station. The third was a block away from Friedrichstraße, which is the brightest place in the center of the city (at least according to VIIRS). The results of the three measurements are shown below:

The plots are similar to the ones I showed in an earlier blog post. The vertical axis shows how bright or faint the stars are. Stars I said I couldn't see are shown in red, stars I wasn't sure about are shown in blue, and stars that I said I could see are shown in black. The horizontal axis shows the time since the measurements were started (each small tick is one minute).

The horizontal lines show the estimate (maximum likelihood fit) of how bright the sky was at each location. With a few assumptions, it's possible to turn this value into a very rough estimate of how many stars you can see. In Dahlem, about 300 stars could be seen with that level of skyglow, in Spreebogenpark about 200, and near Friedrichstraße around 100. By comparing the three datasets you can see that the app is really working, and that in each location my results are quite self-consistent. Unfortunately, I didn't happen to have an SQM with me to check how closely these results compared to the actual sky radiance.

I am continuing to learn a lot about the stars and constellations by using the app!  Since September I now know learned the stars Vega and Deneb and the constellation Cygnus (the swan) very well.  I am also slowly getting used to Perseus. I think that all of the stars I wasn't sure about were in the (very sparse) constellation Draco.

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