Finding the Galactic Center
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Our galaxy is a collection of billions of
stars arranged in a flattened disk with
spiral arms.
Image credit: Wikipedia
Astronomers locate objects in the sky
using a coordinate system similar to
the system of latitude and longitude
we use on the surface of the Earth.
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This system measures position north or
south of a celestial equator that is an
extension of the Earth’s equator into
space in units of degrees.
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It also measures position around the
celestial equator in units of hours and
minutes. The full 360 degree sweep
of the sky is divided into 24 total
hours with 1 hour of right ascension
equal to 15 degrees of arc.
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Image credit: http://wind.caspercollege.edu/~marquard/astronomy/celestial_sphere.htm
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Globular clusters are collections of
thousands of stars bound to one
another by gravity.
Image credit: Wikipedia
Several dozen of these clusters are
known to orbit the center of our
galaxy in a roughly spherical shape.
By finding the center of these clusters,
we can find the center of the Milky
Way Galaxy.
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This exactly what astronomer Harlow
Shapley did in the early 19th century.
He noticed that the globular clusters of
the Milky Way were very skewed
toward one particular direction in the
sky.
Image credit: Wikipedia
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He realised that if he could locate the
center of the globular clusters, he
would be able to find the center of the
Milky Way Galaxy.
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Distances to the clusters are given in
units of kiloparsecs. A kiloparsec
(kpc) is 1,000 parsecs with 1 parsec
equal to about 3.26 light years.
A light year is the distance light travels
in a year. It is about 10 trillion
kilometers (6 trillion miles).
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You will plot the values of right
ascension on the right ascension
graph. Values are given in hours (h)
and minutes (m).
Right ascension graph provided by Dr. Robin Ciardullo, Penn State University
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Declination graph provided by Dr. Robin Ciardullo, Penn State University
You will then plot the values of
declination (+ or – values in degrees).
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On each graph, you will determine the
“average” value. These average values of
right ascension and declination will locate
the center of the globular clusters and the
center of the Milky Way Galaxy.
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