THE MILKY WAY

By: Cole Watanabe

&

Shimon Masaki

What is the Milky Way?

It is the galaxy in which the Solar System is located. (We’re part of the Milky Way!)

It is one of hundreds of billions of galaxies in the observable universe.

How big is it?

• Estimated to be about 13.2 billion years old• Nearly as old as the Universe• There was a gap of almost 5 billion years

between the formation of the Galactic halo and the thin disk

Formation

The Milky Way might not have formed through the merger of several smaller galaxies as previously thought.

“We haven't yet understood how it did form,” (Manuela Zoccali of the Department of Astronomy and Astrophysics at the Pontifical Catholic University )

History and Discovery

• There are many creation myths around the world which explain the origin of the Milky Way and give it its name.

• In the Baltic languages the Milky Way is called the "Birds' Path" (Linnunrata in Finnish), since the route of the migratory birds appear to follow the Milky Way.

• Aristotle himself believed the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which is continuous with the heavenly motions."

• The Neoplatonist philosopher Olympiodorus the Younger (c. 495-570 A.D.) criticized this view, arguing that if the Milky Way were sublunary it should appear different at different times and places on the Earth, and that it should have parallax, which it does not.

• The Arabian astronomer, Alhazen (965-1037 AD), refuted this by making the first attempt at observing and measuring the Milky Way's parallax, and he thus "determined that because the Milky Way had no parallax, it was very remote from the earth and did not belong to the atmosphere."

• Actual proof of the Milky Way consisting of many stars came in 1610 when Galileo Galilei used a telescope to study the Milky Way and discovered that it was composed of a huge number of faint stars.

• The first attempt to describe the shape of the Milky Way and the position of the Sun within it was carried out by William Herschel in 1785 by carefully counting the number of stars in different regions of the visible sky. He produced a diagram of the shape of the Galaxy with the Solar System close to the center.

Structure

HaloThe spheroid halo consists of old stars

and globular clusters, of which 90% lie within 100,000 light-years of the galactic center.

About 40% of these clusters are on retrograde orbits, which means they move in the opposite direction from the Milky Way rotation.

The disk contains gas and dust which obscure the view in some wavelengths, the spheroid component does not.

Sun’s locationThe Sun (and therefore the Earth and the

Solar System) may be found close to the inner rim of the galaxy's Orion Arm

The Orion–Cygnus Arm is a minor spiral arm of the Milky Way galaxy some 3,500 light years across and approximately 10,000 light years in length.

Spiral wingsEach spiral arm describes a logarithmic spiralA logarithmic spiral is a special kind of spiral

curve which often appears in natureThe Milky Way possesses only two major

stellar arms: the Perseus arm and the Scutum-Centaurus arm.

Outside of the major spiral arms is the Monoceros Ring (or Outer Ring), a ring of gas and stars torn from other galaxies billions of years ago.

Galactic CenterThe galactic disc, which bulges outward at

the galactic center, has a diameter of 70,000–100,000 light-years

The intense radio source named Sagittarius A*, thought to mark the center of the Milky Way, is newly confirmed to be a supermassive black hole.

What You Need To Remember…

Some of the names of Milky Way’s structure: Halo, Sun, Spiral Wings, Galactic Center.

William Herschel made the first attempt to describe the shape of the Milky Way.

It is about 13.2 billion years old. In the Baltic languages the Milky Way is

called the "Birds' Path"

Video

Doesn’t this make you feel insignificant?

Works Cited  Lodriguss, Jerry. "MILKY WAY." Catching the Light: Astrophotography

by Jerry Lodriguss. Web. 07 Feb. 2011. <http://www.astropix.com/HTML/D_SUM_S/MILKYWAY.HTM>.

Oak, Manali. "Facts About the Milky Way - The Galaxy." Buzzle Web Portal: Intelligent Life on the Web. Web. 07 Feb. 2011. <http://www.buzzle.com/articles/facts-about-the-milky-way-the-galaxy.html>. 

Smith, Gene. "The Milky Way Galaxy." Center for Astrophysics and Space Sciences @ UCSD. 28 Apr. 1999. Web. 07 Feb. 2011. <http://casswww.ucsd.edu/public/tutorial/MW.html>.

WETHINGTON, NICHOLOS. "Facts About the Milky Way." Universe Today. 11 July 2009. Web. 07 Feb. 2011. <http://www.universetoday.com/22285/facts-about-the-milky-way/>.