Physics Photo of the Week
Pinwheel Galaxy M101
Several galaxies can be found in
Ursa Major (Big Dipper). M101 (appropriately named the "Pinwheel
Galaxy") is one of the best examples of a face-on spiral galaxy.
This image was made by astronomy students: Emma Berger-Singer, Forrest Brown, Sean
Moffitt, and Phil Waidner with assistance from Donald Collins on
April 24, 2008. The telescope is an 8-inch aperture telescope
fitted with an SBIG CCD camera.
Galaxies are very distant and very large objects in the universe.
A galaxy such as this contains about 100 billion stars and lies abot 11
million light years distant. The Milky Way Galaxy (our home
galaxy), is believed to resemble this galaxy - about 100 thousand light
years across. In the Milky Way the
Sun and the Solar System exist as a tiny spec about half-way between
the core and the outer perimeter. About 100 million solar system
diameters will fit in the 100 thousand light years of the galaxy's
diameter. If we made a model of a galaxy where the Sun and all
the planets occupied a 1 milimeter circle, the whole galaxy would
consist of a model about 100 km in diameter - a distance from
Asheville, NC to the Great Smoky Mountains National Park.
As the pinwheel indicates, the galaxy is
rotating. About 2 million years are required to complete one
rotation. However the stars rotate faster near the core than on
the periphery due to the laws of gravity.
Most of the 100 billion stars lie within the core of spiral
galaxies. The disk consists mainly of dust, which is invisible
but absorbs starlight. (See PPOW
for Nov. 11, 2005) The spiral arms indicate where the dust
has accumulated and piled-up partly due to the fact that the inner
revolve more quickly than the the outer regions (see the leaf-litter
piles from rainflow last October 19 PPOW). The mass
of the galactic dust actually forms new stars in clusters along the
spiral arms. Several regions of new star clusters can be seen
along the spiral arms in M101, especially in the spiral on the left
edge of the galaxy photo.
Photo of the
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an interesting phenomena in
the world around us. Students, faculty, and others are invited to
submit digital (or film) photographs for publication and
explanation. Atmospheric phenomena are especially welcome.
Please send any photos to email@example.com.
All photos and discussions are copyright by Donald
Collins or by the person credited for the photo and/or
discussion. These photos and discussions may be used for private
individual use or educational use. Any commercial use without
written permission of the photoprovider is forbidden.
here to see the Physics Photo
the Week Archive.
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