Oxford-based astronomer Clark's favorite celestial objects, novae and supernovae, prove to be admirable looking glasses by which to view the universe. Novae, of course, are not new, despite their names. A supernova is the spectacular explosion of a massive star as it dies. The core collapses and the stellar envelope falls in--only to bounce back, creating a shock wave that blasts the old star out into space. Novae are more like hiccups, as Clark puts it, occurring in binary star systems when an older dense white dwarf begins to suck in material from an expanding companion star. The material is compressed, heated, and may ignite--producing an explosive burst. Without the nuclear reactions occurring in massive stars, there would be no heavy elements--gold, silver, platinum--to seed interstellar dust nor cosmic rays to provide heat sources. In his account of these phenomena, Clark reserves the more technical matters for appendices, enabling him to describe the historical/mythical/astronomical tradition in lay terms, with anecdotal material for color. We learn of the historic debate on the dimensions of the Milky Way between a brash Harlow Shapley and a more orderly Heber Curtis, and note that the theories of Franz Zwicky and Walter Baade--who together coined the terms nova and supernova in 1937--were virtually laughed at. Clark goes on to describe present-day searches for novae and calculations as to their numbers: one should appear every 50 years or so, yet few are recorded. (Among possible reasons: we don't see that much of the galaxy, explosions may occur by day.) Clark also speculates on earthly effects should a supernova appear nearby--changes in the ozone, and potential lethal effects of cosmic ray fallout. His angle of vision allows him to dwell on themes current in today's popularizations--like the age, size, and fate of the universe--but these are relatively peripheral. For interested readers from high school up: a fresh, pleasing approach and a fine job.