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Transcript
Star clusters and constellations
Star clusters are groups of stars that are ‘connected’ by a significant gravitational force ands
move around tougher as the galaxy rotates. The motion of the Sun through the galaxy does
not affect the appearance of a star cluster from Earth over a long period of time. Examples of
star clusters are the Great Cluster (M13) in the constellation of Hercules and some of the
stars in the Pleiades. M13 is a globular cluster and the Pleiades an open cluster.
However a constellation is a group of stars that appear to be related simply because of the
view of them from the Earth. They may be at very different distances from the Erath and so
as time passes the appearance of the constellation will change. This change will be very
slow and differences are only seen over some hundreds of thousands or years. Examples of
constellations are Orion, Ursa Major, Taurus, Perseus, Cassiopeia etc.
The three photographs show M13, the Pleiades and part of the constellation of Orion.
The following diagrams show how the constellation appears from the Earth and then a ‘side
view’ from a point far out in space showing how the stars are spread out at different
distances. Betelgeuse lies at only 310 light from the Earth while delta Orionis is another 2000
light years further away and yet still seems to be part of the same constellation when viewed
from the Earth. The three stars in the belt (zeta, epsilon and delta) are 1108, 1206 and 2347
light away respectively.
Betelgeuse
Rigel
2000
Distance (light years)
1000
The stars in M13 are all around 25 000 light years away. M13 is a huge cluster containing a
few hundred thousand stars.