Clyde’s planet

There were nine in the bed
And the little one said
“Roll over,
Roll over!”
So they all rolled over
And one fell out,
There were eight in the bed
And the little one said
“Roll over…”

Among the planets, however, it was the eight big bullies who stayed in the bed and the little one who had to fall out, to the dismay of many Americans, including children. They hadn’t actually seen Pluto – it’s very difficulty to see – but from 1930 to 2006 it had counted as the one planet that had been discovered by Americans.

It arrives on July 6 at opposition – the middle of the best time for seeing a planet. With Pluto, that’s a more than usually relative matter. (Is it as grammatically sinful to say “more relative” as to say “very unique”?)

The view at midnight (called 1 PM by shifted summer clock time) between July 5 and 6. The moment of Pluto’s opposition is 10 Universal Time. Pluto is up in the middle of the sky, but fainter than myriads of stars not shown.

Pluto at its brightest (now magnitude 13.6, and getting fainter each year as it moves outward) is 700 times fainter than the faintest star that can be seen with the naked eye on a perfect night. Still, Pluto is more within the reach of skilled amateur telescopists than the even more distant members of the class of objects to which it’s now known to belong, and that’s why I keep including a page about it in the Astronomical Calendar. If you seriously want to try to see it you can use the detailed chart in the Pluto section there.

The story has been often told. Percival Lowell believed that there was yet another planet to be found beyond Neptune, as Neptune had been discovered beyond Uranus and Uranus beyond Saturn, so at his Lowell Observatory on Mars Hill above Flagstaff in Arizona he employed Clyde Tombaugh to do the searching. Tombaugh was a young Kansas farmer and also an amateur astronomer, and had caught the professionals’ attention with detailed drawings of Mars and Jupiter that he had made with a homemade telescope, so he evidently had the patience for the task and could be employed cheaply (as Robert Burnham later was).

And the task: it was to take thousands of photographs with one of the observatory’s telescopes and pore over them with a “blink comparator” – an apparatus that kept switching between two photographs taken on different dates, so that any “star” that moved could be detected.

The moving pinpoint of light that he at last found was named Pluto partly for Percival Lowell’s initials, but we have gradually acknowledged that it was not Lowell’s missing planet, being far too small and in an un-planet-like orbit. It was really Clyde Tombaugh’s discovery.  When Clyde visited Furman University in 1990 and talked to the students, I pulled out my sketchbook but could have plotted him a little more exactly than this, in which he is about as distant and minimal as Pluto in your telescope.

There is at least one more chunk of Pluto’s story that I’d like to talk about, but there should be another chance for that because the New Horizons spacecraft is to arrive at Pluto this month.