Johannes Kepler

Johannes Kepler was an astronomer and mathematician who lived in the late 1500s and early 1600s. He was born in 1571 in the town of Weil der Stadt, in what is now Germany. Kepler is known for explaining how planets move in space. He worked during a time when ideas about the universe were changing. Many people still believed Earth was the center, but Kepler supported a Sun-centered system.

Kepler studied mathematics and astronomy at school. Mathematics is the study of numbers and shapes. Astronomy is the study of objects in space, such as planets and stars. Kepler became a teacher and later worked as an assistant to the astronomer Tycho Brahe. Tycho Brahe had collected very careful records of planet positions. These records showed where planets appeared in the sky over many years.

After Tycho Brahe died, Kepler used these records to study the motion of planets. He focused especially on the planet Mars. Kepler noticed that the paths of planets were not perfect circles. Instead, he found that planets move in shapes called ellipses. An ellipse is a shape like a stretched circle. This idea was different from older models that used only circles.

Kepler described his findings as three rules, now called Kepler’s laws of planetary motion. A law, in science, is a rule that describes how something works in nature. The first law says that planets move in ellipses around the Sun. The second law explains that a planet moves faster when it is closer to the Sun and slower when it is farther away. The third law shows a clear link between a planet’s distance from the Sun and the time it takes to complete one orbit.

An orbit is the path an object follows as it moves around another object. For example, Earth’s orbit is the path it takes around the Sun. Kepler’s laws helped explain why planets appear to change speed and position in the sky. His work matched careful observation and used mathematics to describe these movements clearly.

Johannes Kepler wrote several books about astronomy. One of his most important works is called Astronomia Nova, which means "New Astronomy." He lived a difficult life and moved often because of war and illness. Kepler died in 1630. His ideas were later used by other scientists, including Isaac Newton, to further describe motion and gravity. Kepler is remembered for giving a clear description of how planets move around the Sun.