The Milky Way Galaxy By: Rachel Williams & Deidre Vaughters

Size The Milky Way is about 100,000 light years in diameter It is said to be about 1,000 light years thickness. It was estimated that The Milky Way contains at least about 200 billion stars possibly even 400 billion. The stellar disk is a much thicker disk of gas. The gaseous disk has a thickness of 12,000 light years.

Age Scientist said that it is extremely difficult to define the age of which Milky Way was formed. The age of the oldest star was discovered yet about 13.2 billion years ago. Astronomers Luca Pasquini, Piercarlo Bonifacio, Sofia Randich, Daniele Galli, and Raffaele G. Gratton used the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure the beryllium content of two stars in globular cluster NGC 6397.Very Large Telescope measureberyllium globular clusterNGC 6397

Compositions and structure Spitzer Space Telescope in 2005 backed up previously collected evidence that suggested the Milky Way is a barred spiral galaxy.Spitzer Space Telescopebarred spiral galaxy Consists of a bar- shaped core region surrounded by a disk of gas, dust and stars.gas, dust In the disk region are several arm structures that spiral outward in a logarithmic spiral shape. The mass distribution within the Galaxy closely resembles the Sbc Hubble. logarithmic spiral

Sun’s Location It takes the Solar System about 225–250 million years to complete one orbit of the galaxy (a galactic year),[33] so it is thought to have completed 20–25 orbits during the lifetime of the Sun and 1/1250th of a revolution since the origin of humans. galactic year[33]origin of humans

Environment The Milky Way and the Andromeda Galaxy are a binary system of giant spiral galaxies. Andromeda Galaxy binary system Together with their companion galaxies they form the Local Group, a group of some 50 closely bound galaxies. The Local Group is part of the Virgo Supercluster.Local Group Virgo Supercluster The Milky Way is orbited by two smaller galaxies and a number of dwarf galaxies.dwarf galaxies The largest is the Large Magellanic Cloud with a diameter of 20,000 light- years.Large Magellanic Cloud It has a close companion, the Small Magellanic Cloud. The Magellanic Stream.Small Magellanic Cloud Magellanic Stream

Velocity Many astronomers believe the Milky Way is moving at approximately 600 km per second relative to the observed locations of other nearby galaxies. The recent estimates range from 130 km/s to 1,000 km/s. The Galaxy is moving at 600 km/s, Earth travels million km per day, or more than 18.9 billion km per year, about 4.5 times its closest distance from Pluto.Pluto

Discovery A Greek philosopher Democritus was the first known person to propose that the Milky Way might consist of distant stars.Greek philosopher Democritus proof 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. Galileo Galilei telescope Thomas Wright, speculated that the Milky Way might be a rotating body of a huge number of stars, held together by gravitational forces akin to the Solar System but on much larger scales.Thomas Wright gravitational forces A disk of stars would be seen as a band on the sky from our perspective inside the disk.

Facts All the stars that we can see at night are part of our own Milky Way Galaxy. Like other spiral galaxies we can view from space, the Milky Way Galaxy is disk-shaped spiral with a central bulge. The diameter of the disk is approximately 100,000 light years; the central bulge is about 16,000 light years. Our solar system is located on a spiral arm of the Milky Way Galaxy, about two thirds of the way out from the center. The center of the Milky Way is surrounded by a spherical halo of about 150 globular clusters. A globular cluster is a densely packed ball of stars containing hundreds of thousands or even millions of stars. The stars of globular clusters are low in metals and were thus formed when the Galaxy was young and less highly evolved.

Facts The central region of the Galaxy contains old stars and little in the way of dust and gas. The disk of the galaxy contains gas, dust, younger stars with more complex chemical compositions, and active regions of star formation like the Orion nebula.

Facts 90% of the matter in the universe is nonluminous. Our Galaxy is centered in a halo of nonluminous dark matter that may be ten times larger than the visible portion of the spiral disk. It takes our Sun about 200 million years to complete one orbit of the center of the Milky Way. Like other distant galaxies, our own Milky Way Galaxy is a flat spiral with dark lanes. We can see dark lanes from inside the galaxy. In this time exposure, the dark rift in the Milky way can be seen starting in the constellation of Cygnus.

Facts Under dark summer skies, it is possible to see this dark rift in our own galaxy with the naked eye. A band of dust and other nonluminous matter that cuts a visible rift in the plane of a galaxy by obscuring the light from stars. Many fuzzy objects (nebula) are visible in the night sky, and are included in the catalog of Messier Objects, which the 18th century French astronomer Charles Messier compiled to aid him in his search for comets.

Facts Diameter of M.W. Disk 120,000 light years Radius of Central Bulge 6,000 light years Thickness of M.W. Disk 1,000 light years Distance (Earth to Galactic Nucleus) 30,000 light years Period for Solar System (sun, earth, etc.) to circle M.W. 225,000,000 years Number of Stars in the Milky Way 100,000,000,000 (1011) Total Mass of Milky Way 7.2 X 1011MSUN or 1012MSUN

Facts We cannot see the center of the Milky Way with visible light, but infrared, radio, and x-rays show much. It is likely that a giant black hole lives at the center.

Facts The light year is a measure of distance. Light travels 186,282 miles in one second. A light year is the distance that light travels in one year, or 5,880,000,000,000 miles.

Milky Way