On Periodic Motion -- On Electromagnetism and Gravity -- The Calendar, the Day and the Hour -- Highways in the Sky -- Flickering Candles: Cepheid variable stars -- Stars that Breathe.

This book provides a brief and pedagogic introduction to a variety of topics, with a common motif that they all occur, in some way or other, in “the sky”, and involve some sort of “rhythm”. Sky is not just the inside of a dome; there are many strata, each with its own beauties and mysteries. As we go up, the atmosphere thins out and ends, and we move into the space, into the realms of planets, asteroids, and comets, and even further, beyond the solar system into the vast Milky Way galaxy. This is where the night sky comes in, with all its twinkling stars, the stars in our own galaxy. We must use telescopes to explore further. In this book, we will start from the ancient astronomers and how they studied the motion of earth through space. Study of planetary orbits, from Kepler and Newton to Einstein, had been fascinating. We will try to take the reader through the wonderful worlds of the cepheid variables and pulsars to the strange oscillations of the neutrinos and the new eye to look at the universe, namely the gravitational waves. The book stops at the discovery of the black hole at the center of our galaxy, but that is just because we must stop somewhere, or the assortment could go on ad infinitum. Some of these topics are highly mathematical in nature, but we will try to avoid the complicated mathematics as much as possible, without compromising with the rigor.