On the Cover: Comet Hyakutake provided the best celestial show in decades when it passed by Earth on its way to swing around the Sun. In late March and early April, the comet grew so bright that it was even visible in the light-polluted skies of major cities in the northern hemisphere. This photograph, however, was not taken in a major city: the comet appears over Kenai, Alaska, where the city lights barely dimmed the comet's glowing tail. Millions of people around the world who rarely glance at the night sky were enraptured by the unexpected visitor. With luck, their interest will be captured again next spring, when comet Hale-Bopp—with the potential to be even brighter—flies through our neighborhood. Bill Hutchinson
4 Belize: Rosetta Stone of the K/T Boundary: Adriana Ocampo reports on The Planetary Society's continuing series of expeditions to explore this turning point in evolutionary history
6 Geology and Climate Change: Mechanisms of Extinction: Kevin Popediscusses the horrific processes that could have wiped out over half the species living on Earth.
7 Impact Processes: Reconstructing the Events: Michael Rampinogives an idea of what it would have been like to see the K/T object hit Earth (from a safe place!).
8 Mineralogy: Carved in Stone: Alfred Fischerdescribes how evidence can be found in the tiniest of details—in the types of rock and what they are made of.
10 Stratigraphy: Layers of Evidence: David Kingtells us how the rocks blasted out by the K/T impact can tell us much about its aftermath.
12 Comet Hyakutake: A Very Pleasant Surprise: Charlene Andersonpresents stunning images of this surprise visitor that put on a magnificent show for nearly everyone on Earth.
14 Why Near-Earth Objects? Carl Saganexplains how NEOs are crucial to understanding the history and future of the solar system.
3 Members' Dialogue SETI debate.
15 World Watch Future missions for the ESA and NASA; Russian rockets.
16 News & Reviews Reporting on missions: Voyager vs. Galileo.
17 Society News Celebrating Viking's 20th anniversary; watching comets.
18 Basics of Spaceflight Electrical systems.
20 Q&A How do we know what types of signals detected by SETI warrant investigating?