Astronomy On-Line

How Clear is your Sky?

Mapping the Light Pollution

In many places in Europe and elsewhere the stars do not seem as bright as they used to be. Streetlights and atmospheric pollution have caused the night sky to be less dark and less clear than 20 or 30 years ago. The beauties of the night sky cannot be enjoyed from many European cities.

Many of the light fittings used in streets are wastefully directing up to half of the light into the sky. The Campaign for Dark Skies believes that excessive lighting can be controlled so that the light is directed only downwards. Astronomers need to enjoy well-lit streets, but they require modern, good quality lighting.

Minimising light pollution also saves precious energy resources. The amount of greenhouse gases released into the environment by power stations can be reduced.

You can contribute to a survey of how clear the skies are in your area. We are asking you to observe some stars and send your results in to be put on an all-European survey.

All you need to do is to go outside and note which of the numbered stars you can see with your unaided eye. You can do your observations on several nights and send in the results for the best night.

If you normally wear glasses then be sure to put them on for this experiment! And please also tell us if you have excellent, medium or poor eyesight.

How to participate

We want you to contribute to measuring the light pollution in Europe! Who of you are located at dark sites and who of you are in places where the light pollution is high?

This can be done by looking for the faintest stars you can see with the naked eye. Stellar brightnesses are measured in magnitudes (of then written as mag): the brightest stars are about 0 mag, the faintest to the naked eye about 6 mag (or 5 or even 7). We want to find out what is the magnitude of the faintest star you can just see.

stars in November

Sky Chart (November)
(Click on image to get an enlarged version)

Here is the sky as you see it in mid-November in the evening, at about 21 hours. You can easily identify some of the main constellations like the Greater Bear (in Latin: Ursa Major, abbreviated as UMa) and Cassiopeia (Cas). Between these, you will see the Lesser Bear (Ursa Minor or UMi) the brightest star of which is the North Star, or Polaris. You may print this chart if you would like to take it with you for the observations.

UMi enlarged

Sky Chart with the area around Ursa Minor enlarged
(Click on image to get an enlarged version)

Here is the constellation of the Lesser Bear enlarged. The numbers next to the stars indicate their magnitudes. You should print this chart and take it with for the observations.

Now it is your turn!