How much do the shapes of constellations change over thousands of years?
The stars in the sky are constantly in motion as they orbit the center of the
Milky Way. From the Earth, a change by, say, 2 - 3 degrees would be enough to
distort many of the recognizable constellations. Most of the stars that make
up the brighter constellations are within a five hundred light years of the
Earth ( my estimate), and have proper motions of about 0.1 arc seconds per
year. This means that it would take about 40,000 years for them to drift
by 1 degree in the sky ( 1 degree = 3600 arc seconds ) and so, between
40,000 and 100,000 years you would expect the average constellation to have
its stars shifted by a few degrees. The mean direction of this shift is
towards the constellation Lyra towards which the solar system is moving.
After, say, 500,000 years, the typical star would be shifted by 10 degrees and
for most constellations, this would be enough to render them unrecognizable.
The above figure shows what happens to the Big Dipper (Ursa Major) after another 10,000 years.
Copyright 1997 Dr. Sten Odenwald
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