A long-period comet discovered on 1858 June 2 by the Italian astronomer Giovanni Battista Donati (1826–73); formerly designated 1858 VI. In 1858 September it reached magnitude −1. Perihelion, 0.58 au, was on 1858 September 30, with closest approach to Earth (0.5 au) on October 9. Around this time the comet showed a prominent curved dust tail resembling a scimitar, for which it is famous. At best, this dust tail stretched for 60°, with two thin, straight ion tails at a tangent to it. The nucleus threw off shells of material as it rotated. The comet’s orbit has a period of nearly 2000 years, eccentricity 0.996, and inclination 117°.0.