Galileo
Galileo contributed information about the Milky Way through his use of telescopes pointed towards the skies. Using his telescopes, Galileo was able to see stars which were too faint to the unaided eye. With this new found information, he attempted to put all the stars he knew and found into star systems. These new, "invisible" stars that he found seemed to be very important to understanding nebulae and the Milky Way. Now, instead of just thinking that the Milky Way some sort of painting in the skies from the gods, Galileo began to think that the Milky Way was actually a view of the very far stars from Earth. Overall, Galileo's contribution was verifying that the Milky Way is made up of stars.
William Herschel
William Herschel's contribution to understanding the nature of the Milky Way was finding the shape of the Milky Way. Being interested in finding nebulae, Herschel thought that some were in separate galaxies. When he discovered one of the many nebulae having a star in its center, he proved wrong the theory that nebulae were not able to hold stars in them. Trying to search for more information about these stellar objects, Herschel went to make bigger and bigger telescopes. Thinking that the Milky Way was a nebula, he wanted to find out how it was shaped. He accomplished this by measuring the distances to as many stars as he could which he found to be in a circular band around the sky suggesting a disk shape. He also tried to find the thickness of the Milky Way, however, he had no way of measuring the actual distances, at least accurately. With the help of Herschel, we are now able to understand that our galaxy is the shape of a flat disk with a bulge in the center.
Shapley believed that everything in space was located inside our own galaxy which he thought was 300,000 light years in diameter. He believed that the Sun was not at the center of the galaxy (he thought it was 50,000 light years away from the center) and said that spiral nebulae were actually as clouds inside the Milky Way as well. Shapley went on finding the size of the Milky Way by observing globular clusters. He thought that all globular clusters were around the same size and used their size to find out how far away they were. He made the discovery that the center of the globular distribution is where the center of the galaxy is.
Edwin Hubble
Hubble was one of the few who believed that the spiral nebulae were not in the Milky Way but rather they were other entire galaxies outside our own. He tried to prove this by making a reflector telescope which allowed him to see the star in the Andromeda Galaxy. But to prove that it was another galaxy, instead of a nebulae, Hubble had to try to find its distance. He found the distance by using the Cepheid variables in the Andromeda Galaxy which he used to find that this "nebulae" was 25x farther away than most stars in the Milky Way. Soon in 1925, Hubble also made a classifying system for the galaxies by their shape such as spiral, elliptical, or irregular. Lastly, Hubble was also the one who proved the expansion of the universe. He saw that the farther the object was, it had more of a redshift. He showed that the redshifts of galaxies meant that they were moving outwards of about thousands of miles per second. He made Hubble's Law which states that redshifts increase in their proportion to their distance away from us. He also made Hubble's constant which is the velocity of a receding galaxy divided by the distance to it.
RR Lyrids and Cepheids
Cepheids are a type of variable stars. A variable star is a star that changes in brightness over a period of time. These types of stars were actually named after the star Delta Cephei which varied in magnitude after 5.367 days. Henrietta Leavitt was the first to notice this type of variable star, most of them found in a near by small companion galaxy called the Small Magellenic Cloud where she observed that the brighter stars took longer to change their brightness. Cepheids are around 1000x the brightness of the Sun and are driven by pulsing. They are rare stellar objects and their period depends on their metallicity. They change in brightness due to expand and contracting. These stars can be used in finding the distances of other galaxies and clusters. An example of this is When Edwin Hubble used the star Delta Cephei to indicate that the Andromeda Galaxy is outside of the Milky Way
RR Lyrae variable stars are the brightest in the variable star group. They are like Cephiads but are less luminous and have a shorter variability period. These stars are old and have a low mass but are more common than Cephiads
Immanuel Kant
Kant agreed with the theory that the Milky Way was a disc of stars but he was the first to suggest that other nebulae could also be discs of stars in 1755. He said that the tiny, dim nebulae were actually other galaxies or "island universes". Kant also made a nebular hypothesis which explained how our solar system was formed but used it generally to the Milky Way and the universe which expanded the view on how the universe was made and opened up possible ideas that there could be other galaxies.
Henrietta Leavitt
Leavitt, on her way to finding variable stars, she found that the Cepheid variable in the Small Magellanic Cloud were all the same distance from the Earth. She also studied the period-luminosity relationship of these stars which with she was soon able to find that the distance from the stars are up to ten million light years. With the help of Ejnar Hertzsprung, they both were able to find the distances of different stars. With Harlow Shapley they were able to measure the size of the galaxies. Edwin Hubble would use her work to fin the age of the universe.
Heber Curtis
Heber believed that the Sun was near the center of a smaller galaxy and thought that spiral nebulae were galaxies outside the Milky Way. He believed that globular clusters were outside the galaxy but thought that they were much closer to one another. He made a theory that spiral nebulae were similar to the Milky Way using the optical spectrum as proof as the spectrum for the spiral nebula and the galaxy were the exact same. He also thought that the spiral nebulae were large collections of stars far away from the Milky Way.
"The Great Debate"
The Great Debate was also known as the Shapley-Curtis Debate which was a time when astronomers had very different theories on what the structure of the Universe and how it was formed. Harlow Shapley and Heber Curtis both disagreed with each other on how the universe was composed. Harlow believed that everything in the universe was inside our own galaxy while Curtis believed that spiral nebulae were actually outside the Milky Way and were actually other galaxies. They both disagreed on how far away the globular clusters were which Curtis thought was closer and said that our galaxy was smaller than Shapley believed it to be. It was found that Curtis' theory was correct when Edwin Hubble settled the conflict by finding the distance of the Andromeda galaxy. Shapley was correct in saying that the Sun was far from the center of the Milky Way. He was also correct in his estimate of the total size of the Milk Way.
No comments:
Post a Comment