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 problem of surviving the incredible acceleration that the explosion would cause. Ardan suggests that Barbicane and Nicholl travel with him in the projectile, and the offer is accepted. In the end, the projectile is successfully launched, but the destinies of the three astronauts are left inconclusive. The sequel, "Around the Moon", deals with what happens to the three men in their travel from the earth to the moon. The novel was adapted as the opera "Le voyage dans la lune" in 1875, with music by Jacques Offenbach. In 1880 the Pall Mall Gazette described Verne’s "Columbiad" as a ‘space-ship’ -