On July 23, 1995, veteran observer Alan Hale in New Mexico and Thomas Bopp, looking through a friend's borrowed homemade telescope in Arizona, independently spotted the same fuzzy patch near star cluster M70. Hale emailed the Central Bureau for Astronomical Telegrams three times; Bopp drove to a Western Union and sent an actual telegram. This episode tells the story of the Great Comet of 1997, discovered at a record 7.2 astronomical units from the Sun with a nucleus roughly 37 miles across, six times the size of Halley's Comet, and visible to the naked eye for 569 days, shattering the nine-month record set in 1811.

The conversation explains why peak brightness lagged behind perihelion on April 1, 1997, what the comet's rare third tail of neutral sodium atoms revealed about the momentum of light, and how its heavy water ratio, twice that of  ...