Science at Parramatta High
M7
Ptolemy's Cluster
— February 2001 —

This splendid cluster was known to Ptolemy who mentioned it about 130 AD. He described it as the "nebula following the sting of Scorpius".

M7 (named in Charles Messier's famous catalogue of "non-comet" objects) is an open cluster about 800 light years from earth.

Open (or galactic) clusters are physically related groups of stars held together by mutual gravitational attraction.

This photo was taken with a 400mm f.l. f/6.3 telephoto lens, piggy-backed on an equatorially mounted telescope. The exposure was 60 seconds, guided. Film was 400 ASA colour print.

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