The correct answer to this question is option 3, Johannes Kepler. Johannes Kepler was a German astronomer and mathematician who lived in the late 16th and early 17th centuries. He is best known for his three laws of planetary motion, which provided a significant breakthrough in our understanding of the movement of the planets.

Prior to Kepler, the prevailing belief was that the planets moved in perfect circles around the Sun. However, Kepler`s meticulous observations and mathematical calculations showed that the actual paths of the planets are elliptical, meaning they are shaped like elongated circles.

Kepler`s work was based on the earlier heliocentric model proposed by Nicolaus Copernicus, so it is easy to see why option 4 (Copernicus) might be a tempting choice. However, Copernicus did not provide evidence for the elliptical paths of the planets; that was discovered by Kepler.

Galileo Galilei, option 1, was a contemporary of Kepler and made significant contributions to the field of astronomy, but he did not directly demonstrate the elliptical paths of the planets.

Option 2, Martin Luther, is not relevant to the question and can be disregarded.

In summary, Johannes Kepler was the astronomer who first demonstrated that the planets move around