North Carolina Milky Way
Dave Wilson, of northern Buncombe County near Asheville, NC photographed this excellent picture of the Milky Way in December, 2012. I had never seen the Milky Way in the Winter from my home in North Carolina. From North Carolina I have only seen the Milky Way in the the late summer and early fall when the much brighter parts of the Milky Way are visible near the southern horizon. Congratulations to Dave Wilson for the excellent photo! Click on the image to see a larger picture.
Dave's camera (a Nikon D90) is so sensitive and shows so
many stars that picking out the familiar constellations and
stars is nearly impossible. At right the contrast has been
reduced to make the brighter stars of Cassiopeia more
visible along with the constellation familiar stick figure
as an "M". I have also outlined part of Cygnus, the
Northern Cross, in the lower left part of the modified
photo. Click on the photo to see a larger version.
The Milky Way is the disk-shaped spiral galaxy where the
Sun and the Solar System reside. The milky appearance
crossing through the night skies arises from the millions of
stars (like the Sun) that populate the disk. Think of
the galaxy resembling a double sided Frisbee - a flat disk
with a thick hub in the middle. Since the Sun and the
solar system are in the galaxy disk, looking in any
direction along the plane of the disk sees more stars than
in the other directions. The "milky river of stars" is
our galaxy's disk seen edge-on from inside the disk.
We also see dust clouds causing the dark patches along the
Milky Way. Dust in the disk obscures some stars that
are further away and also provide the fuel to form new stars
over time scales of hundred of millions of years. The
Sun was "born" out of a dust cloud about 4 billion years
ago. The Milky Way galaxy is huge! The disk is
about 100 thousand light years across.
Dave's photo is also very interesting in that it
captured another galaxy. At the top of the main photo,
the elongated smallish cloud is the Milky Way's closest
spiral galactic neighbor - M31, the Great Galaxy in
Andromeda. The Andromeda galaxy is similar in
structure to the Milky Way (a huge spiral of 100 billion
stars and dust clouds, 100,000 light years across), but the
Andromeda galaxy is about 2 million light years
distant. Thus the starlight from the Andromeda galaxy
captured by Dave's camera last December left the galaxy when
human ancestors were just beginning to roam the Earth - long
before any recorded history. The light from the the
bright stars in Cassiopeia (within our galaxy) left those
stars only about 400 years ago at the dawn of modern
astronomy when Galileo first used a telescope to examine
stars and planets.
Also visible in Dave's magnificent photograph in the
upper right center is the double cluster (h and chi
Persei). These two clusters are about 7000 light years
distant - still within the Milky Way disk - containing large
bright stars that formed about 10-100 million years
ago. That is very young for stars compared to the
Sun's 4 billion years' age. Thank you, Dave!
Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature 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 firstname.lastname@example.org.
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.