Dark Adaptation

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When you move from a really bright room into a darkened one, it takes a little while for you to see clearly. This is because certain muscle groups in your eyes need to be activated to allow your pupils to dilate. The bigger your pupils get, the more light your eyes can gather from your surroundings, and the more you can see. Many psychotropic drugs engage these muscle groups – that’s why your pupils dilate when you’re on them.

Giving your pupils time to dilate and adjust to low light settings is called dark adaptation. Since observing happens at night, you need to dark adapt your eyes beforehand to prepare them. Under normal circumstances, this takes around 30 minutes.

There are a few things you can do to speed up the dark adapting process, and to make your stargazing session comfortable without ruining pupil dilation:

1. Protect your eyes during the day. Light from the Sun is so bright that it can delay your night-time dark adapting by up to half an hour. The best way to avoid this is to:

  • limit your exposure to direct sunlight
  • wear dark sunglasses during the day to filter out sunlight
  • wear a hat/hoodie/scarf to block light coming from the top/sides of your sunglasses

2. Only use red light at night. Red light doesn’t interfere with pupil dilation the way normal light does, so you can comfortably use it to navigate during your observing sessions. Useful tools include:

  • A red LED torch/headtorch (you can also use a normal one covered with a red filter sheet)
  • An internal red filter on your phone (Android users can download an app called Twilight; iOS users can check out this accessibility shortcut)

3. Keep your telescope eye covered. With a telescope, you only use one eye to observe. Since your eyes can dark adapt independently of one another, you can use an eyepatch to cover your observing eye.


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