Why is the direction of position v upwards?

The wave is moving from left to right (as indicated by the arrow), so, given that at the current instance the amplitude of the position V is 0 (or whatever midpoint the dashed line corresponds to), in the immediately next instance the position will continue increasing as the wave moves from left to right. The peak currently shown at U will at some point "arrive" at V. At that point the location V will have the maximum amplitude. After that the direction at position will be downward, etc.

kepler used the data from tycho blahe (his mentor) to construct the laws of planetary motion.