Four hundred years ago when
Galileo discovered
the moons of Jupiter, the satellites appeared in his primitive
telescope
as tiny, almost infinitesimal specks of light pirouetting around
the giant planet. Their discovery transformed 17th century cosmology
and made Galileo famous, but he never saw them as anything more
than star-like pinpricks. The "Galilean satellites" were
second-class citizens in the heirarchy of known worlds.
What would Galileo say now?
On August 16th, Philippine astrophotographer Christopher
Go used a modern 11-inch
Celestron telescope to photograph Io casting its shadow on Ganymede.
"I captured this rare event through a hole in the clouds, "
says Go. "It was a lucky clearing!"
In the movie, Io and Ganymede reveal themselves as fully-formed
worlds with surface markings and a spherical shape. Io's circular
shadow cuts a dark swath across Ganymede, transforming that giant
moon (it is larger than Mercury) into a succession of crescents
rarely seen by observers. Indeed, as far as we know, no telescope
on Earth or space has ever photographed one of Jupiter's moons casting
its circular shadow so clearly across another.
"While imaging the shadow transit, I took the time to photograph
Jupiter itself, " says Go. "The Great Red Spot, an anticyclone
twice the size of Earth, was very
prominent."
At this point, one imagines Galileo would jump up and exclaim--"bring
me a telescope!" If only we could. August 2009 is a superb
time to watch the giant planet. Jupiter is at its closest to Earth
and outshines every star in the night sky. Backyard optics reveal
giant storms, clouds, moons, moon shadows and occasionally an explosive
surprise. Jupiter is in the South at midnight, in mid-to-late August 2009:
US $.99
