Short answers, pulled from the story.
Cosmology is the study of the nature of the universe, covering its origin, large-scale structure, evolution, and ultimate fate. It is investigated by scientists including astronomers and physicists, as well as philosophers including metaphysicians and philosophers of space and time. Physical cosmology is a sub-branch of astronomy focused on the universe as a whole.
The word cosmology first appeared in English in 1656 in Thomas Blount's Glossographia, with the meaning "a speaking of the world". In 1731, German philosopher Christian Wolff used the term in Latin as cosmologia to denote a branch of metaphysics dealing with the general nature of the physical world.
Belgian priest Georges Lemaitre proposed the Big Bang model in 1927. He is considered the father of the Big Bang model. His theory described a universe that began in an initial high-density state he called the "primeval atom" and then expanded outward.
According to astronomers reporting at the Planck 2014 meeting in Ferrara, Italy on the 1st of December 2014, the universe is 13.8 billion years old. The more precise measurement from the Lambda-CDM model places the age at 13.799 plus or minus 0.021 billion years.
Astronomers at the Planck 2014 meeting reported that the universe is composed of 4.9% atomic matter, 26.6% dark matter, and 68.5% dark energy.
The Great Debate was a dispute between cosmologists Heber Curtis and Harlow Shapley over whether spiral nebulae were separate galaxies or objects within the Milky Way. It reached its peak on the 26th of April 1920 at a meeting of the U.S. National Academy of Sciences in Washington, D.C. Edwin Hubble resolved it in 1923 and 1924 by detecting Cepheid variable stars in the Andromeda Galaxy and establishing that their distance placed them well beyond the edge of the Milky Way.