Dark Adaptation


When you move from a really bright room into a darkened one, it takes some time before you can see in the dark. This is because certain muscle groups in your eyes need to be activated to allow your pupils to dilate (get bigger). 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 expand to the size of dinner plates 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 (i.e. no LSD), 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 your precariously achieved big pupils:

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 mess with your pupils 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 really only use one eye to do all your observing. Since your eyes can dark adapt independently of one another, you can use an eyepatch to cover your observing eye while you do other stuff, and switch it to the other eye to look through the scope. This way you:

  • don’t have to sit still for half an hour while both your eyes dark adapt
  • can cover your inactive eye while observing so you don’t have to squeeze it shut
  • can call yourself a Space Pirate ( ͡° ͜ʖ ͡°)

Other Useful Articles:

Apps To Track Phases of the Moon

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