Fifteen years ago on this day, the comet Hale-Bopp made its closest approach to Earth, at a distance of 1.315 AU (1 AU = 93 million miles). The comet had been discovered independently by two amateur astronomers, Alan Hale of New Mexico and Thomas Bopp of Arizona, nearly two years earlier on July 23, 1995, when it was outside of Jupiter's orbit (7.15 AU). Even though Comet Hale-Bopp didn't come particularly close to Earth, because of its unusual brightness and large size it was visible to the naked eye for 19 months, the longest ever recorded for a comet, besting the previous record-holder, the Great Comet of 1811, by ten months. Above, a picture of the comet a week after it reached its closest point, taken from Croatia. The image has been voted one of the finest in the English Wikipedia.

Below, recent Pictures of the Day:

Image: Wikimedia Commons.