Friday, July 14, 2017

Great observation from Portugal

I wanted to share a great observation made a few months ago by a Loss of the Night project participant from Portugal:

As you can see, there is a very clear separation (white line) between the stars that were visible (yellow, orange, and brown) and those that were not (black). You can also see how thanks to the observer examining so many stars, you can have a lot of confidence in the result, and can even measure how consistent the observer's result is. When you first start using the app, you might not have results as consistent as this, but with a bit of practice it becomes easier and easier to cover a lot of stars quickly.

This also demonstrates why the app is a better method for estimating limiting magnitude in bright places than star chart based methods like Globe at Night. In this case, the naked eye limiting magnitude was around 3.9 ± 0.1. The star charts of Globe at Night only allow you to choose between integer limiting magnitudes, which in this case would be "about 4". In addition, with Globe at Night we can't be sure how careful a participant is, and we found that compared to skyglow models, the standard deviation of Globe at Night observations is about 1.2 magnitudes.

While the app can provide more accurate data, I want to stress that it's not a replacement for Globe at Night! The app doesn't include stars with limiting magnitudes above about 5.2, so in areas with little light pollution, Globe at Night is a better method. In addition, the Globe at Night time series goes back over 10 years, and there is therefore a lot of value in continuing to contribute to it. In my opinion, it's the best system we have for tracking global changes in skyglow. So please consider contributing to both projects!

If you make an observation with the app, you can easily see a similar plot for your own results. Just head to My Sky at Night, zoom in to the area where you made your observation, and click on it to bring up this chart.

No comments:

Post a Comment