What are "p" and "r" wrt the moon? Still learning, thinking - and failing - about the moon.
timeanddate.com has this cute and dynamic moon sketch at e.g. https://www.timeanddate.com/moon/uk/london

They generate this based on three parameters that they call i, p and r. The above image is the result of invoking this: https://www.timeanddate.com/scripts/moon.php?i=0.028&amp;p=3.388&amp;r=0.035.
I know that i stands for i llumination in the range 0-1.
However, what are p and r and in what unit? What are the likely correct terms? r appears to be some sort of &quot;rotation angle&quot; of the moon while p is the same for the &quot;mask&quot;.
Yes, the are angles in radians. With &quot;i=0.5&quot; to make things clearer:

$p=0$ is the right half illuminated
$p=\pi/2=1.57$ is top half illuminated  (rotated anticlockwise by 90 degrees)
$p=\pi=3.14$ is left half illuminated  (rotated 180 degrees)

and so on.
The r parameter is the rotation of the moon, so $r=0$ is &quot;lunar north up&quot; $r=pi/2$ is rotated anticlockwise by 90 degrees.