Which did Kepler notice FIRST about planetary motion that caused him to propose Kepler’s first law of orbital motion? *
1 point
a. The planets have circular orbits.
b. The distance between Mars and the sun is constant.
c. The planets speed up and slow down but cover the same area.
d. Most planets have highly elliptical orbits.
c. The planets speed up and slow down but cover the same area.
To determine which observation led Kepler to propose Kepler's first law of orbital motion, we can analyze each option:
a. The planets have circular orbits: Kepler did not observe this first. In fact, Kepler noticed that planetary orbits were not perfectly circular.
b. The distance between Mars and the sun is constant: Kepler did not observe this either. Instead, he discovered that the distance between any planet and the sun changes as the planet moves along its orbit.
c. The planets speed up and slow down but cover the same area: This observation by Kepler is known as the law of equal areas. However, it is not the primary observation that led him to propose Kepler's first law.
d. Most planets have highly elliptical orbits: This is the correct observation that Kepler noticed first. By studying the positions of the planets, he realized that their orbits were not circles but rather ellipses.
Therefore, the correct answer is d. Most planets have highly elliptical orbits.