Number 81 (Story #3), May 27, 1992 by Phillip F. Schewe and Ben Stein GEMINGA IS A GAMMA-RAY PULSAR . Data from two orbiting observatories---the x-ray satellite Rosat and the Gamma Ray Observatory---show that Geminga, an object in the Gemini constellation, bears a resemblance to Vela and the Crab, two pulsars that emit gamma rays. Unlike them, however, Geminga seems to shine mostly at gamma wavelengths, a fact which had baffled scientists ever since Geminga was discovered twenty years ago. The new satellite observations show that gamma and (more weakly) x-ray broadcasts from Geminga are modulated (in pulsar style) with a period of 237 msec. The rate at which the neutron star at the heart of Geminga is slowing down leads to an estimate of 300,000 years for the age of the pulsar. (Nature, 21 May 1992.)