Near-Earth object focused on asteroids and short-period comets. CNEOS even restricts its definition of NECs to short-period comets—, 107 such objects have been discovered. , only 20 comets have been observed to pass within of Earth, including 10 which are or have been short-period comets. Two of these comets, Halley's Comet and 73P/Schwassmann–Wachmann, have been observed during multiple close approaches. The closest observed approach was 0.0151 AU (5.88 LD) for Lexell's Comet on July 1, 1770. After an orbit change due to a close approach of Jupiter in 1779, this object is no longer a NEC. The closest approach ever observed for
From the Earth to the Moon the Moon. It seems appropriate to us to share with you some of the reflections of the crew as the modern-day Columbia completes its rendezvous with the planet Earth and the same Pacific Ocean tomorrow." In "Back to the Future Part III", Clara Clayton in 1885 asks Emmett Brown if he believes mankind will ever "travel to the moon the way we travel across the country on trains." Being from the future Doc already knows that doesn't happen for another 84 years, but he affirms they will while quoting a passage of "From the Earth to the Moon". Clara calls