Four hundred years ago, the German astronomer Johannes Kepler described his concept of the laws of planetary motion in his work, "Astronomia nova". These important laws remain important concepts for students of physics, and those who work with such students will find much of interest on this particular site. Created by David P. Stern (a retired physicist at the Goddard Space Flight Center), the...

Humans have long been interested in looking up into the sky and trying to figure out the nature of the planets, the sun, and the moon. Many ancient civilizations were able to systematically observe the sky and eventually they worked out mathematical schemes to describe what they found there. In this compelling article by Sandra M. Caravella, she takes a close look into how they were able to make...