In 1900, the planets were known to have 22 satellites or moons. The number of known moons has now more than quadrupled and is still increasing.
Discovery of the Satellites of Mars
The scientists of Laputa "discovered two lesser stars, or satellites, which revolve about Mars; whereof the innermost is distant from the primary planet exactly three of his diameters, and the overmost five; the former revolved in a space of ten hours, the latter in twenty-one and a half."
— Johnathan Swift, Gulliver's Travels, 1726
Phobos and Deimos
Mars' moons were actually discovered a century and a half later by Asaph Hall (1829-1907) at the Naval Observatory in Washington, DC. Hall named the satellites for the sons of Ares (Mars) in Greek mythology, Phobos, and Deimos (meaning fear and terror, respectively).
The rings of planets, such as those of Saturn, are a system of countless small satellites. In 1977, it was discovered that Uranus was also encircled by a system of rings. Uranus' rings were discovered because they occulted (blocked from view) a star as Uranus passed between the Earth and the star. The discovery of Uranus' rings occurred through observations made from the Kuiper Airborne Observatory. The discovery telegram (shown at left) sent by Kuiper observers is on display in the Exploring The Planets exhibit in the National Air and Space Museum.