Will you join us in turning off the lights?

On 25 September 2022 an extraordinary experiment is happening in Leiden: Seeing Stars Leiden. The more lights are turned off, the less light pollution there will be, and therefore the more stars we will be able to see in the night sky.

How can you join us?

From 22.00 to 23.30 at night on 25 September all of the lights will go out. How can you help?

  • Turn off your own lights, go outside, and look up at the stars.
  • Share your experience on social media with #SeeingStarsLeiden
  • Help scientific research: “How much light pollution is there in Leiden?”
Check the project area

Help measure light pollution!

With all of us working together we can map where and how much light pollution there is in Leiden and the region - and how much light pollution is removed during Seeing Stars Leiden.  The more people who join us, the more accurate our measurements will be.

How can you measure?

  1. Download the Android app via Google Play  or the iOS app via the App Store.
  2. Take a first measurement before Seeing Stars Leiden (for example at 21:30 in Sunday the 25th).
  3. Take a second measurement during Seeing Stars Leiden between 22:00 and 23:30 hrs.
  4. You can take measurements from different locations to map more of the light pollution in Leiden. With measurements before and during the event we can measure how much light pollution we have removed!
Daan Roosegaarde in de Leidse Sterrewacht.

Android: 'Loss of the Night’

With ‘Loss of the Night’ for Android, you indicate whether or not you can see specific stars clearly. The app will guide you to finding those stars. Based on your answers we can indicate the level of light pollution in that area. You will be asked to find 8 stars, but you can search for more stars to improve the accuracy of your measurement.

  1. Look for a specific star with the help of the app,
  2. When you’ve located it on your screen, look for the same star in the night sky,
  3. Indicate whether you can see the star clearly or not,
  4. If it cannot be seen clearly, indicate why,
  5. Press the ‘Submit’ button.
Complete image

iOS/iPhone: 'Dark Sky Meter’

With ‘Dark Sky Meter’ for the iPhone you take a light measurement using your camera. This measurement represents sky brightness as a light factor relative to an ideal starry sky. The more measurements you take, the more accurate the light pollution map will be.

  1. Take a darkness measure by fully covering up your camera and pressing on the ‘Dark’ button,
  2. Take a light measure by pointing your camera straight up at the sky, and pressing on the ‘Sky’ button,
  3. Indicate the weather conditions,
  4. Press the ‘Submit’ button.
Complete image

Seeing Stars Leiden - Data Map

The data gathered by both mobile apps is shown on a map that indicates the varying levels of light pollution across Leiden and the surrounding region. We care about your privacy and only collect the light measurement, and the location, date and time of the measurement.

Information about the nature of this data - measured following the Bortle scale - can be found on this Wikipedia page.

Take a look at the map

Where do you experience light disturbance?

Would you like to report a specific instance of light pollution that you experience as disruptive? You can do that on the ‘ Lichthinder Kaart’ developed for the ‘Night of Nights’: www.nachtvandenacht.nl/lichthinder.