long-period comet remarkable for its anomalous second tail, which projects toward rather than away from the Sun. It was one of the brightest naked-eye comets of the 20th century. It was discovered photographically on the night of Nov. 8–9, 1956, by S. Arend and P. Roland at the Royal Observatory, Uccle, Belg. Its perihelion passage (i.e., its closest approach to the Sun) occurred on April 20, 1957. Because it was discovered months before perihelion, lengthy observations could be carried out. The anomalous tail appeared for a few nights late in April, changing direction from night to night and appearing as a sharp spike aimed at the Sun. This was an effect of perspective, of viewing edgewise a fan of debris from the comet, scattered ahead of it along its orbit.