Definition of A Double Planet
There has been some debate in the past on precisely where to draw the line between a double-planet and a planet–moon system. In most cases, this is not an issue because the satellite has a small mass relative to its host planet. In particular, with the exception of the Earth–Moon and Pluto–Charon systems, all satellites in the Solar System have masses less than 0.00025 (1⁄4000) the mass of the host planet or dwarf planet. On the other hand, the Moon to Earth mass ratio is 0.01230 (≈ 1⁄81), while the Charon to Pluto mass ratio is 0.117 (≈ 1⁄9).
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—Florence Nightingale (1820–1910)
“No man, not even a doctor, ever gives any other definition of what a nurse should be than this—”devoted and obedient.” This definition would do just as well for a porter. It might even do for a horse. It would not do for a policeman.”
—Florence Nightingale (1820–1910)
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