Pluto and the Occult: Rare events illuminate Pluto’s atmosphere
By Ron Cowen
Twice in the past month, astronomers were given a rare opportunity to peer through the tenuous atmosphere of Pluto. For a few minutes on July 20 and again on Aug. 21, Pluto passed directly between Earth and stars in the constellation Ophiuchus.
During such events, called occultations, Pluto casts a moving shadow across Earth as it blocks a star’s light. Starlight passing through Pluto’s atmosphere bends, or refracts, and some is absorbed. The amount of dimming and the specific wavelengths absorbed reveal information about the temperature, density, and composition of the frigid planet’s atmosphere.