Trick Allows Scrutiny of Pluto’s Moon

Michael Schirber at

Near midnight of July 11, several telescopes in Chile caught a rare and wonderful sight:  the shadow of Pluto’s moon, Charon, as it passed in front of — or occulted — a distant star.

The observations, now being analyzed, may pin down the size of the moon and whether or not it has an atmosphere.  Preliminary indications from one group seem to suggest little or no gaseous envelope.

Charon blocked the light of the relatively faint star C313.2, casting a shadow that was roughly the same size as the moon itself — around 630 miles wide.  A previous occultation by Charon of a different background star was observed in 1980, but only one telescope — with limited precision — managed to observe that event. 

To have eight major telescopes and three separate astronomy teams recording this most recent alignment is considered very fortuitous — especially since a year ago no one knew that this shadowy event would happen at all.

More here.