Milky Way Galaxy
If you go out into the countryside on a clear summer night, far from city lights and look up, you will see a band of light arching across the vault of the sky. In Ancient Greek and Roman legend, this was a milky river that flowed across the sky. They called it the Milky Way, inadvertently christening the galaxy in which we live.
Seen through binoculars or a telescope, the true nature of the Milky Way is apparent; it is composed of billions of stars, so numerous and distant that they all blur together when observed with the naked eye. Our galaxy is a flat spiral, but since we are inside looking out, we do not see a spiral structure. The band of light we see curving across the sky is one of the galaxy's spiral arms.
As late as 1918, it was believed that the Milky Way was the only galaxy in the universe. It was believed to be about 10,000 light-years across, and our Sun was thought to be located at its center. (A light-year is the distance that light, moving at nearly 186,282 miles [300,000 km] per second, travels in a single year. That is about 6 trillion miles [9.6 trillion km].)
A better understanding of the size of the Milky Way came through the work of American astronomer Harlow Shapley. He studied objects called globular star clusters, which he noticed were centered around the Sagittarius area of the sky, and devised a method of calculating the distance to them.
Shapley's results established a radically changed concept of the size of the Milky Way. He deduced that the system is actually 300,000 light-years across, and the Sun was 50,000 light-years from the center. He later shook the scientific community by maintaining claiming that there were many other galaxies in the universe, not just one.
A major supporter of Shapley's hypothesis was Dutch astronomer Jan Hendrik Oort. He was able to show that the center of the Milky Way, the area around which the stars are rotating, was also located in the direction of the constellation Sagittarius. Why a great glowing mass of stars is not visible in that area of the sky is due to the large amount of dust and gas blocking our view. Oort's calculations, based on new information, resulted in a downsizing of the Milky Way. The numbers that are accepted today are 100,000 light-years in diameter, about 2,000 light-years thick, with the sun 30,000 light-years from the center.
The Sun is orbiting around the galactic center at about 130 miles (210 km) per second, and it takes 200 million years to complete a single orbit. It is estimated that there are over 100 billion stars in the Milky Way galaxy. This spinning pinwheel also contains star clusters, planets, comets, dust, glowing gasses and black holes, to name a few of its components.
Analysis of the motion of material near the centers of galaxies suggests the presence of supermassive black holes, perhaps ranging up to a billion solar masses, at the galactic centers. Such a celestial Charybdis may indeed exist at the center of our own Galaxy. The motion of gas near the center of the Milky Way indicates that there must be a tremendous concentration of mass at the Galaxy's center -- yet there is no obvious visible object that could comprise this mass. The mass must be concentrated in a very small area, leading a number of researchers to believe a supermassiv black hole must be there.
Older stars and denser clusters are located near the center of the galaxy; younger stars and open star clusters extend farther out. The Sun can be considered to be in the periphery of the Milky Way.
Because of the obstructed view of the center of the galaxy, astronomers use instruments other than optical telescopes to study the galactic core. Radio waves and infrared waves are not blocked by dust as severely as visible light, so radio and infrared telescopes can provide much more information. Optical telescopes can be used to observe other galaxies that are face-on to us and, since we have no reason to believe that the Milky Way is unique, what we see in the core of other galaxies will permit us to make assumptions about our own.
This is the complete article, containing 708 words
(approx. 2 pages at 300 words per page).
