Walter Lewin

“His laws changed all of physics and astronomy. His laws made it possible to calculate the mass of the sun and planets. The way it's done is immensely beautiful. If you know the orbital period of any planet, say, Jupiter or the Earth and you know its distance to the Sun; you can calculate the mass of the Sun. Doesn't this sound like magic?We can carry this one step further - if you know the orbital period of one of Jupiter's bright moons, discovered by Galileo in 1609, and you know the distance between Jupiter and that moon, you can calculate the mass of Jupiter. Therefore, if you know the orbital period of the moon around the Earth (it's 27.32 days), and you know the mean distance between the Earth and the moon (it's about 200,039 miles), then you can calculate to a high degree of accuracy the mass of the Earth. … But Newton's laws reach far beyond our solar system. They dictate and explain the motion of stars, binary stars, star clusters, galaxies and even clusters of galaxies. And Newton's laws deserve credit for the 20th century discovery of what we call dark matter. His laws are beautiful. Breathtakingly simple and incredibly powerful at the same time. They explain so much and the range of phenomena they clarify is mind boggling. By bringing together the physics of motion, of interaction between objects and of planetary movements, Newton brought a new kind of order to astronomical measurements, showing how, what had been a jumble of confused observations made through the centuries were all interconnected.”