A double object

A double object

Fig. 15.3 . The Hubble Space Telescope, abbreviated HST, distinguishes between Pluto, the bright object at the middle of the central image, and its companion Charon, which is the fainter object in the lower left of the central image. Observations from telescopes on Earth (left) were unable to clearly resolve the pair because of atmospheric distortions. At the time of the HST photograph, Charonís orbit around Pluto (right) was seen nearly edge on, and Charon was near its maximum angular separation from Pluto, a mere 0.9 seconds of arc. Plutoís diameter is 2.32 thousand kilometers, Charon is half that size, and the two objects are just 19.64 thousand kilometers apart. The HSTís ability to distinguish Plutoís disk at its distance of 4.4 billion (4.4 x 109) kilometers is equivalent to seeing a baseball at a distance of about 100 kilometers. (Courtesy of NASA.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University