Thumb with sand grain held below the full moon.
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The Hubble Telescopes's Advanced Camera for Surveys (ACS), installed in 2002,
has a square field of view, 3.4 mins of arc across - one ninth the width of the Moon.
It captures only a small portion of the sky - about as much as would be covered
by a grain of sand balanced on the tip of a thumb held at arm's length.
The Hubble Telescopes's Wide Field Planetary Camera (WFPC),
in use from 1995 to 2002 had an irregular field, 2.7 mins of arc across.
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