Once in a blue moon == 1.16699016 × 10-8 hertz Posted by eCa on Friday July 31, 2015 @08:10PM from the google.com dept. https://www.google.com/search?q=once+in+a+blue+moon ( 2 comments | 10 points | on HN )
[1] https://en.wikipedia.org/wiki/Pitch_drop_experiment