Anyone know what this formula does?

hi guys, im currently trying to figure out a formula which i got from

In the script they have this formula

var rbit:Number = Math.sin(Math.PI/180 * theta);
var rbit90:Number = Math.sin(Math.PI/180 * (theta - 90));

Can anyone explain to me how does that work? or what does this formula do??

thank you so much