Which did Kepler notice about planetary motion that caused him to propose Kepler’s first law of orbital motion?

The motions of the planets  in the solar system made Keppler propose the laws of planetary motion.

Explanation:

The motions of the planets  in the solar system made Keppler propose the laws of planetary motion.In simple words, Kepler's first law can be defined as all planets moved around the sun in the elliptical orbit having the sun as one of the foci.Kepler’s first law means that planets move throughout the Sun in elliptical orbits. An ellipse is a shape that follows a levelled circle.

I’d say a : water molecules