2551443 is the length of the synodic month in seconds. The calculation being done converts the current time in seconds into a 512-wide integer range representing the lunar phase by offsetting from the lunar phase during the unix epoch.

Every field has somebody five standard deviations out to the right. Don't let that mistake you into thinking you're too far to the left. The fact that you can appreciate such an accomplishment, already puts you a standard deviation to the right.