... A Mystery in Gamma Rays . ... Like falling stardust, cast off bits of comet Swift-Tuttle hurtle through the upper atmosphere about this time each year as planet Earth passes near the comet's orbital path. ... Tycho and Copernicus: Lunar Ray Craters . ... Dazzling in binoculars or a small telescope, the Moon is pocked with impact craters. ... Farewell Jupiter . ... The Cassini spacecraft, launched from Earth four years ago, has now swung past Jupiter and should arrive at Saturn in the year 2004. ...