Kelley, of the University of Maryland, said the comet that was most formative for him was Hale-Bopp—the bright one that I remember seeing from my dorm room, in 1997, and which won’t return again until the forty-fourth century.

Source: https://www.newyorker.com/science/elements/what-the-green-comet-tells-us-about-the-past-and-the-future