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February 19 is the birthday of Nicolaus Copernicus, born in 1473. With the posthumous publication of his opus De Revolutionibus Orbium Coelestium in 1543, Copernicus is credited with starting the Scientific Revolution by stating that the planets orbit the Sun rather than Earth. This ran counter to what was taught by the Catholic Church and led to a series of battles between science and religion that reverberated for centuries. During this period, Galileo Galilei, Johannes Kepler, and Isaac Newton made significant advances in the understanding of gravitation and planetary orbits.



Students can explore how planets orbit the Sun using the Orbital Motion – Kepler’s Laws Gizmo. In the Gizmo, students can control the initial velocity of a planet moving around the Sun and observe the resulting orbit. They will see that planetary orbits are elliptical, that planets speed up when they are closer to the Sun, and that orbits are independent of planetary mass. One of the most interesting things to observe is that, by zooming in on the Sun, you can see that the Sun actually makes a small elliptical orbit just like the planet. This makes sense when you consider that, just as the planetary orbit is shaped by the gravity of the Sun, the Sun’s (much smaller) orbit is shaped by the gravity of the planet.