Galaxy M51 - The Whirlpool Galaxy
This impressive spiral galaxy is a favorite target for amateur and professional astronomers alike. It consists of a "whirlpool" of about 100 billion stars. M51 is estimated at about 23 million light years from Earth, which means the light we see today is the light that originated 23 million years ago.
From the focal length of the telescope that photographed
this galaxy we can find the angular size in degrees, or
other angular units. Simple geometry from the angular
size we find a diameter of the spiral to be 35,000 light
years - considerably smaller than our own Milky Way Galaxy's
diameter of about 100,000 light years. The spiral
structure of many galaxies arises from the piling-up of
interstellar gas and dust into bigger clouds eventually
forming new stars in the clouds. The clouds exhibit
spiral structure because the inner clouds orbit the core
faster than the outer clouds. Eventually - after
several billion years - the spiral structure becomes more
and more tightly wound.
The photograph actually contains two galaxies. The
cloud near the top of the photo is a separate galaxy (NGC
5195) that is either approaching M51 or is moving past
it. The outer spiral arm of M51 actually extends all
the way and connects with the smaller galaxy. The
other spiral arm close to the satellite appears to be
distorted by the tidal gravitational interaction with the
satellite. All the distinct stars scattered throughout
the image are members of our own Milky Way galaxy. M51
and its companion are too distant and the stars are too
numerous to see the individual stars.
Compare this image of M51 with the Andromeda Galaxy (PPOW
November 15, 2013). The Andromeda Galaxy is only
1/10 the distance (2 million LY) of the Whirlpool and about
100,000 LY across. The image of Andromeda Galaxy last
November was made with a much smaller telescope in order to
fit the whole large galaxy into the frame of the camera.
This image was made with the 14 inch telescope in the
College View Observatory on March 23, 2014. The
telescope was donated to Warren Wilson College for the
College View Observatory by alumnus Gary Starkweather class
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