How to calculate the phase of the moon very, very badly!!

This talk is about how, despite “common knowledge”, lunar cycles are not 28 days long, and in fact lunar cycles don’t have a single numerical length! You’ll hear about several very bad ways to calculate the phases of the moon, why they seemed reasonable at the time, and exactly how it took three years from the time one app shipped to the App Store before the calendar was even arguably correct.

Transcript

1. Everyone Knows a Lunar Cycle is 28 Days or, falsehoods werewolves believe about time
9. 27.321661 days a sidereal month
10. ...two years later...
11. M T W Th F S Su                           
12. M T W Th F S Su                           
13. M T W Th F S Su                           
14. M T W Th F S Su                           
15. ⁉ ⁉ ⁉ ⁉
16. sidereal schmidereal
17. lunar phases are synodic months
18. synodic months are 29.530587981 days
19. averages are lie-candy for your brain
20. thanks BDAstroCalc!
21. 0 0.5 0.9
22.                           
23.                           
24.                            0.5235? 0.6852? 0.9855?
25.         0.614 0.638 0.652 Feb 2 Feb 3 Feb 4 When is the half-moon?
26. midnight 02/23 midnight 02/24 midnight 0.46 0.49 0.52  
27. Victory!!!
28. witchy.co witchy.co/trig andre.arko.net twitter.com/sailorhg twitter.com/indirect