Alex Filippenko

Today's telescopes are designed to provide huge light-gathering mirrors at relatively low cost. The mirrors focus light from distant objects onto sensitive electronic detectors that are far more efficient than traditional photographic film.

In 1543, Copernicus proposed a heliocentric system, in which Earth and other planets orbit the Sun, which is at the center of the Universe. In the early 1600s Galileo provided strong evidence for this model with the newly invented telescope.

Why is the sky dark at night? In an infinitely old and large Universe the sky should be ablaze with light at all times. There are several possible answers to this paradox, each of which has profound cosmological implications. The relative youth of the Universe is now known to be the main explanation.

Supernovae come in several types, based primarily on their spectra. This lecture focuses on the important, hydrogen-deficient subclass called Type Ia, in which a white dwarf robs gas from its companion star and then becomes violently unstable.

In 1995, the first extra-solar planet was discovered around a Sun-like star. Since then, about 200 have been found. The easiest to detect are those with large masses, close to their host stars, and with brief orbital periods.

Is the Universe a finite bubble in a higher-dimensional space? Or, is it infinite regardless of whether it's imbedded in extra dimensions? Will it expand forever or ultimately recollapse? If it does expand forever, how will this limitless future unfold?

Are interstellar voyages possible within a single human lifetime? According to Einstein's special theory of relativity, the answer is "yes" in principle but "no" in practice, given current technology. You explore the reasons for both answers.

Under a new definition adopted in 2006, planets are more narrowly defined and a new class called dwarf planets has been created, which includes Pluto, Eris (a Kuiper-belt object larger than Pluto), and Ceres (the largest asteroid).

This lecture covers the wealth of knowledge about the Moon, a heavily cratered world with extensive lava-filled basins on the Earth-facing side and yet few such features on the far side-which is not perpetually dark.

Astronomers obtain most of their information through the analysis of light. This lecture introduces the electromagnetic spectrum and the technique of spectroscopy, in which light is dispersed into its component colors, as in a rainbow.