Johannes Kepler is known for which scientific contribution?

Johannes Kepler is most famously known for his formulation of the laws of planetary motion, which included the significant discovery that the orbits of planets around the sun are not perfect circles, but rather ellipses. This was a groundbreaking realization that contradicted the longstanding belief in circular orbits and was a pivotal contribution to the field of astronomy.

Kepler's first law, specifically, states that "The orbit of a planet is an ellipse with the Sun at one of the two foci." This insight greatly advanced the understanding of celestial mechanics and provided a more accurate model of the solar system. His work laid the foundation for Isaac Newton's later work on gravitation and motion, as it helped to explain the behavior of planets in a way that could be calculated and predicted.

The other options refer to significant discoveries and advancements in science, but they are attributed to different scientists. The law of universal gravitation, for example, was proposed by Isaac Newton, while the discovery of the first radioactive element is associated with Marie Curie, and the development of the microscope is credited to Antonie van Leeuwenhoek. Kepler's unique contribution focuses specifically on the elliptical nature of planetary orbits, which remains one of the key principles in the study of celestial