Moon phases

Is it possible to make a timer count up from a specific day, let’s say 1970-01-07, to see how many days have passed?
I need this, because i’m recreating moon phases and every 3,69 days it has to switch frames and know on which frame it has to be.

(new Date - new Date(1970,0,7)) / (1000 * 60 * 60 * 24)