THE LONGEST COMET TAIL ever recorded, more than 570 million km, has come to light in the form of a fluctuations in magnetic fields and in the amount and species of charged particles detected by the Ulysses spacecraft on 1 May 1996. A puzzle at first, the fluctuations are now attributed to Ulysses' inadvertent passage through the wake of Comet Hyakutake. The long tail is much greater than that of the previous record holder, the Great March Comet of 1843. If Hyakutake's tail had been visible on Earth at that point in the Comet's trajectory, it would have arced more than 80 degrees across. (Jones et al. and Gloeckler et al., Nature, 6 April /pnu/2000/.)