Astrophysics

The thirty-eighth entry is il moto proprio, and the English name for it, « proper motion », misleads a native speaker rather more than a foreigner. Modern English « proper » means correct, decent, or true to type: a proper meal, the proper procedure, London proper. None of that is meant here. The astronomers took the Latin proprius, which meant one’s own, belonging to this thing and to no other — the star’s own movement across the sky, as against the apparent drift the Earth lends it. English keeps that older sense in a few survivals: « property » is what is one’s own, a « proper noun » names one thing and not a class, and « in his own proper person » still turns up in legal prose. Italian never let it go. Proprio is the everyday word for own — casa propria, con i propri occhi, il proprio nome — so il moto proprio reads to an Italian exactly as it was meant, while the English reader has to be told.