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Welcome to the Extinction-O-Meter wiki! You can expect to find here:

Have fun!

Why should I care about atmospheric extinction?

This question alone deserves more space than the FAQ, so we'll handle this one here.

Atmospheric extinction has a big impact when observing variable stars near the horizon. Since most of the time there will be a difference between the altitude of the variable star and the altitude of comparison stars, light from them gets dimmed differently:

The light from stars placed lower will have to go though a lot more air until reaching the observer, thus getting more dimmed than stars placed higher over the horizon. This can skew the brightness estimate by half of magnitude or more.

To handle this, one possible solution is:

  • consider all stars at the same altitude over the horizon as the variable star
  • and compute what magnitude they should have, to present the observer the same brightness; this is done by multiplying the extinction coefficient to the difference of airmass, then add this to the catalog magnitude of the star
  • then do the interpolation as you'd normally do

All of these steps can be performed easier using the 'Extinction-O-Meter' app. Did we mention that the app can even determine the extinction coefficient for you?

The app itself may look a bit scary, so follow the tutorial.

How do I get set up?

  • Make sure you're connected to the Internet
  • You'll need one of the following browsers: Google Chrome, Internet Explorer 9 or higher, Mozilla Firefox or Opera 30.0 or higher.
  • Access the online PWA.