Introduction to Astrophysics

Define the difference between astrophysics and astronomy. Then study the vast range of scales in astrophysics - from nanometers to gigaparsecs, from individual photons to the radiation of suns. Get the big picture in a breathtaking series of exponential jumps - zooming from Earth, past the planets, stars, galaxies, and finally taking in countless clusters of galaxies.

After touring the universe on a macro scale in the previous episode, now zoom in on the microcosmos - advancing by powers of ten into the realm of molecules, atoms, and nuclei. Learn why elementary particles are just as central to astrophysics as stars and galaxies. Then review the four fundamental forces of nature and perform a calculation that explains why atoms have to be the size they are.

Discover how astrophysicists map the universe. Focus on the tricky problem of calculating distances, seeing how a collection of overlapping techniques provide a "cosmic distance ladder" that works from nearby planets (by means of radar) to stars and galaxies (using parallax and Cepheid variable stars) to far distant galaxies (by observing a type of supernova with a standard intrinsic brightness).

Continue your exploration of motion by discovering the law of gravity just as Newton might have - by analyzing Kepler's laws with the aid of calculus (which Newton invented for the purpose). Look at a graphical method for understanding orbits, and consider the conservation laws of angular momentum and energy in light of Emmy Noether's theory that links conservation laws and symmetry.

Why are the rings around Saturn and the much fainter rings around Jupiter, Uranus, and Neptune at roughly the same relative distances from the planet? Why are large moons spherical? And why are large moons only found in wide orbits? These problems lead to an analysis of tidal forces and the Roche limit. Close by calculating the density of the Sun based on Earth's ocean tides.