Astronomy
Our Galaxy: The Milky Way
Weblecture
The Milky Way
While we are used to looking at amazing pictures of galaxies, it wasn't so long ago that astronomers debated whether stars were evenly distributed through space or clustered together in groups.
In 1921, astronomers Harlow Shapley and Heber D. Curtis both attended the meeting of the national Academy of Sciences in Washington in 1920, and both gave talks into the title "The Scale of the Universe", but each proposed a theory concerning the size of the galaxy and the location of the solar system within it that contradicted the other's theory. Curtis believed the universe was composed of many galaxies concentrations of stars, and is that the sun was near the center of a relatively small galaxy. Shapely believed starts or more equally distributed throughout space and that objects like the Andromeda nebula we're simply gas clouds, also evenly distributed throughout space. He also place the sun far from the center of his single huge Galaxy. The clash of theories became known as "the great debate", but at the time there was no evidence to determine which view was correct.
It wasn't until Edwin Hubble identified Sophia and variables in the Andromeda Galaxy and use their periods to calculate a distance of two million light-years to Andromeda that astronomers were able to show Shapely was wrong about nebula being within our galaxy, but correct in placing the solar system at some distance from the center of the galaxy. Curtis on the other hand was correct about the existence of many galaxies, but seriously underestimated the size of the Milky Way. The debate epitomizes the problems faced by astronomers, especially in the 20th century, where fragmentary and often faulty evidence lead to initially incorrect theories that were subsequently discarded or amended as new led to more complete theories.
Our Own Galaxy
One of the fascinating aspects of the internet is that it can present tons of research in compelling ways. To supplement your text reading this time, take a look at the Galaxy Map website.
Start with the basic plan of the Milky Way, indicated in the first paragraph. Read through the description of the structure of the galaxy, and pay particular attention to the details about the Orion sprayer, where the sun is located. See whether you can find answers to the following questions:
- What kind of stars make up the arms of the Milky Way galaxy?
- What kind of stars make up its central bar?
- What kinds of controversies exist over the number and structure of the arms?
- What is the Orion spur? Why isn't it considered an arm?
Read the page on mapping hydrogen. How well do the hydrogen lanes and the stellar arms overlap?
Read through the information on the Velocity Explorer. What kind of data does it assemble? What do the different colors mean? What can this data tell us?
Take some time to read about The Milky Way Explorer. How does combining information in different wavelengths help us assemble a map of the structure of the galaxy?
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