TROHESE DAYS do the most amazing things. If someoruck a mat the Moon, they could spot the flare. From the tihrobs and wobbles of distant starsthey ihe size and character and even potential habitability of plas muote to be seen—plas so distant that it would take us half a million years in a spaceshipto get there. With their radio telescopes they capture wisps of radiation so preposterouslyfaint that the total amount of energy collected from outside the solar system by all of themtogether since colleg began (in 1951) is 「less than the energy of a single snowflakestriking the ground,」 in the words of Carl Sagan.
In short, there isn』t a great deal that goes on in the universe that astronomers 』t fihey have a mind to. Which is why it is all the more remarkable to reflect that until 1978no one had ever noticed that Pluto has a moon. In the summer of that year, a youngastronomer named James Christy at the U.S. Naval Observatory in Flagstaff, Arizona, wasmaking a routine examination of photographic images of Pluto when he saw that there wassomething there—something blurry and uain but definitely other than Pluto. sulting acolleague named Robert Harrington, he cluded that what he was looking at was a moon.
And it wasn』t just any mooive to the pla, it was the biggest moon in the solarsystem.
This was actually something of a blow to Pluto』s status as a pla, which had never beenterribly robust anyway. Since previously the space occupied by the moon and the spaceoccupied by Pluto were thought to be one and the same, it meant that Pluto was much smallerthan anyone had supposed—smaller even than Mercury. Indeed, seven moons in the solarsystem, including our own, are larger.
Now a natural question is why it took so long for ao find a moon in our own solarsystem. The answer is that it is partly a matter of where astronomers point their instrumentsand partly a matter of what their instruments are desigo detect, and partly it』s just Pluto.
Mostly it』s where they point their instruments. In the words of the astronomer ClarkChapman: 「Most people think that astronet out at night in observatories and s theskies. That』s not true. Almost all the telescopes we have in the world are desigo peer atvery tiny little pieces of the sky way off in the distao see a quasar or hunt for black holesor look at a distant galaxy. The only real work of telescopes that ss the skies has beendesigned and built by the military.」
We have been spoiled by artists』 renderings into imagining a clarity of resolution thatdoes in actual astronomy. Pluto in Christy』s photograph is faint and fuzzy—a piece ofit—and its moon is not the romantically backlit, crisply delied panion orbyou would get in a National Geographic painting, but rather just a tiny aremelyindistinct hint of additional fuzziness. Such was the fuzziness, in fact, that it took seven yearsfor ao spot the moon again and thus indepely firm its existence.
One ouch about Christy』s discovery was that it happened in Flagstaff, for it was therein 1930 that Pluto had been found in the first place. That semi in astronomy waslargely to the credit of the astronomer Percival Lowell. Lowell, who came from one of theoldest ahiest Boston families (the one in the famous ditty about Boston being thehome of the bean and the cod, where Lowells spoke only to Cabots, while Cabots spoke onlyto God), ehe famous observatory that bears his name, but is most indeliblyremembered for his belief that Mars w