Number 44 (Story #2), August 8, 1991 by Phillip F. Schewe and Ben Stein INTERGALACTIC HYDROGEN CLOUDS are more numerous than was previously thought, based on observations made by the Hubble Space Telescope. The spectrum of quasar 3C 273 (2 billion light years away) exhibits various dips, several of which correspond to the absorption (at a particular wavelength, the so-called Lyman-alpha line) of quasar light by hydrogen atoms in intergalactic clouds along the light path to Earth. These absorption lines occur at wavelengths indicative of the clouds' redshift and consequently their distance from Earth. 3C 273 is one of the closest quasars and so the clouds are also relatively near, or, equivalently, young, at least in cosmological terms. Astronomers are therefore puzzled that such clouds could have persisted into present times without evolving much. (Astronomy, Sept. 1991.)