21 February 2010

While reading The Earth Moves: Galileo and the Roman Inquisition I came across this paragraph which reminded me of some of the arguments as to why we needed to remove Pluto’s planetary status: to wit, if we let Pluto remain a planet we will have to make many more objects planets and that will destroy the planetary system we all grew up with (M_ercury^y V_enus^ery E_arth^asygoing M_ars^other J_upiter^ust S_aturn^erved U_ranus^s N_eptune^ine P_luto^ies), which argument is itself inconsistent since we all grew up knowing Pluto was a planet.

When Galileo reported the motions of the moons of Jupiter, it drove certain people to distraction. They refused to believe that he had seen such a thing. “I must write of a harsh objection leveled at me by the astrologers and many of the physicians,” a Neapolitan philanthropist wrote to a scholar at Padua in the spring of 1610. “These people say that if so many new planets are added to the number of those know, this will of necessity ruin astrology and demolish most of medicine, in that the distribution of the houses of the zodiac, the essential dignity of the signs, the quality of the nature of the fixed stars, the records of the star-chroniclers, the government of the ages of men, the months of gestation of the embryo, oh, a hundred and a thousand things which depend on the sevenfold order of the planets – all will be destroyed from their foundation up.” The writer wasn’t convinced by these objections: after all, he quaintly noted, since the luminosity of Galileo’s newly discovered celestial objects was the same as ever, why would their astral influence increase by one iota? But one senses the ferocity of the traditionalists’ resentment. What the eye could detect with this funny “eyepiece-reed,” or cannocchiale, as it was called in Italian, destroyed “a hundred and a thousand things,” reaching into every aspect of human life. They didn’t want to see; the invention was to be a hoax.

That got me to thinking again about what is what in the universe.

The IAU does not have a definition for a sun but by convention it is a star that has planets revolving around it. A star is a self-luminous planetary object. So all suns are stars, but not all stars are suns.

Now the IAU says that a planet must revolve around the Sun. And the only time the word sun is capitalized is when it refers to the star of the solar system to which Earth belongs, also known as Sol.

Therefore, there can be no planets outside of our solar system and since there are no planets anywhere else in the universe there can be no suns anywhere else either since there are no planets to orbit those would-be suns.

So we are stuck with a universe that will be populated, when we find them, by exoplanets revolving around, one would have to assume, exosuns.