Edwin Hubble
- Edwin Hubble showed the scientific community that other galaxies existed beyond our own by proving that what we thought were spiral nebulae are actually other galaxies far outside of the Milky Way
- He used Cepheid variables to measure the distance from us to another nearby galaxy and showed that it was too far away to reside inside of our own
- In 1929, he attempted to provide proof of the expansion of our universe
- the EMR from galaxies is redshifted, indicating that they are moving away from us
- these galaxies are possibly moving away from us at a speed of thousands of miles per second
- the farther away a galaxy is, the greater its redshift (the faster it was moving)
Harlow Shapley
- He used RR Lyrae stars to correctly estimate the size of the Milky Way Galaxy and the sun's position within it. In 1953 he proposed his "liquid water belt" theory, now known as the concept of a habitable zone
- He was the first to realize that the Milky Way Galaxy was much larger than previously believed, and that the Sun's place in the galaxy was in a nondescript location.
- Partook in the debate with Curtis in the “Great Debate” but was incorrect in that
William Herschel
- Herschel ultimately discovered over 2400 objects defined by him as nebulae. (At that time, nebula was the generic term for any visually extended or diffuse astronomical object, including galaxies beyond the Milky Way, until galaxies were confirmed as extragalactic systems by Edwin Hubble in 1924.)
- He also studied the structure of the Milky Way and concluded that it was in the shape of a disk. (the first person to ever come to this conclusion)
Galileo
- Galileo used his telescope to look and view the Milky Way and resolve it into a myriad of individual stars.
- Though the technology of the time was limited, his discovery that the Milky Way was composed of distinct stars has greatly aided our understanding as to the nature of our own galaxy
RR Lyrids & Cepheids - both are different types of variable stars that periodically change their brightness and density as they undergo a period of instability in their stellar evolutionary track
- RR Lyrids
- RR Lyrids are variable stars found in globular clusters and used to measure stellar distances that are too large for spectroscopic parallax to resolve
- More common than Cepheid variables
- Old and of relatively low mass
- Period is typically less than a day
- First identified in RR Lyrae in Lyra
- Cepheids
- Brighter and more massive than RR Lyrids variables
- Used for determining stellar distances
- First identified from Delta Cephei in Cepheus
Immanuel Kant
- The first person to propose that the band of stars in the night sky (we call the Milky Way)
- Proposed that the stars of our galaxy form a broad, flat disk. The Sun and Earth also inhabit this disk. As a result, Kant said, when we look into the disk, we see the combined glow of countless stars, which make up the band of light called the Milky Way. But when we look above or below the disk, we see only a few stars.
Henrietta Leavitt
Heber Curtis
- famous for his role in astronomy's "Great Debate" with Harlow Shapley in which Curtis argued that what astronomers called spiral nebulae were actually spiral galaxies outside our own Milky Way.
“The Great Debate”
- Shapley was arguing in favor of the Milky Way as the entirety of the universe. He believed galaxies such as Andromeda and the Spiral Nebulae were simply part of the Milky Way.
- Curtis on the other side contended that Andromeda and other such nebulae were separate galaxies, or "island universes" (a term invented by the 18th-century philosopher Immanuel Kant, who also believed that the spiral nebulae were extragalactic). He showed that there were more novae in Andromeda than in the Milky Way. From this he could ask why there were more novae in one small section of the galaxy than the other sections of the galaxy
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