913
Lectures Watched
Since January 1, 2014
Hundreds of free, self-paced university courses available:
my recommendations here
Peruse my collection of 275
influential people of the past.
View My Class Notes via:
Receive My Class Notes via E-Mail:

VIEW ARCHIVE


Contact Me via E-Mail:
edward [at] tanguay.info
Notes on video lecture:
Early History of Cosmology
Choose from these words to fill the blanks below:
Friedman, Milne, expanding, moving, electromagnetic, Eddington, Curtis, Messier, Milky, farther, bigger, smudges, experimental, Andromeda, nebulae, 3261, Hubble, balanced, philosophers, explicitly, Lemaitre, Sitter, galaxies, collapse, extrapolation, relativity, constant, egg, island, gravity
the discovery of galaxies
before we began studying the universe in a scientific sense, we learned about                  which are its constituents
but first people didn't know what they were
they were just smudges in the sky, called "              "
first cataloged by Charles               
before this,                          tried to address the question
sometimes called "             universes", what today we call galaxies
until 1920s, basic question: are these nebulae galaxies like the milky way or are they just some                within our own galaxy
Shapley-             debate
inconclusive
Shapley had the wrong answer, that the smudges were part of the Milky Way
Curtis was advocating that there were many galaxies like the            Way
articles were not based on solid                          data
1923 Hubble
Mt. Wilson observatory
found a variable star in                   
comparing the star to stars in our galaxy, he determined that it is much                away than anything in our galaxy
several 100 kiloparsecs away
1 kiloparsec =          light years
so all of a sudden the picture changed from the milky way being the entire universe to it being a much, much              universe
if you want to understand the universe at large in physical terms, the only interaction that actually matters is               
because all other forces are short-range, except                                force, but there charges are mixed so well so that the net electromagnetic field is zero
not so with gravity
gravity cannot be cancelled or compensated
this came in the form of the theory of                     
1917: Einstein
that the universe would                  on itself because of its gravity seemed like a natural thing
proposed the cosmological constant which                  this force of gravity
turned out to be wrong
1917: Willem De             
developed equations for an expanding universe
the discovery of the expanding universe was probably one of the most important scientific discoveries of all time
Vesto Melvin Slipher
Arizona
measured radio velocities of galaxies, later used by             
Knut Lundmark, 1924
Carl Wirtz, 1923
Edwin Hubble, 1929
plotted distances to galaxies against velocities obtained by Slipher
"The Hubble Diagram"
shows that the first away galaxies were, the faster they were             
evidence for                    universe
space expands and carries galaxies apart
Einstein regretted his cosmological                  theory
failed to predict the expansion of the universe even though this was                      contained in his equations and is probably the greatest scientific prediction anyone could make
modern relativistic cosmological models
Alexander                 
1922, Soviet Union, relativity based expanding universe model
George                 
1927, Belgium, look back, it all must have started with in a hot, dense state which he called the cosmic       
not taken too seriously because it was a bit of an                           
1930s relativistic cosmology models
Edward           
the main difference between the Milne model of an expanding universe, and Einstein's model of an expanding universe was that Milne did not assume a priori that the universe has a homogeneous matter distribution
Arthur                   
proved that theory of general relativity was right
the Eddington limit, the natural limit to the luminosity of stars, or the radiation generated by accretion onto a compact object, is named after him
Robertson and Walker
developed mathematical basis of expanding universe

People:

######################### (1730-1817)
French astronomer notable for publishing an astronomical catalog consisting of nebulae and star clusters
  • Messier was a comet hunter, and was frustrated by objects which resembled but were not comets, so he compiled a list of these objects in collaboration with his assistant Pierre Méchain in order to avoid wasting time on them
  • these 100 objects came to be known as the "Messier objects"
######################### (1875-1969)
American astronomer who performed the first measurements of radial velocities for galaxies, providing the empirical basis for the expansion of the universe
  • used spectroscopy to investigate the rotation periods of planets and the composition of planetary atmospheres
  • in 1912, he was the first to observe the shift of spectral lines of galaxies, making him the discoverer of galactic redshifts
  • in 1914, he made the first discovery of the rotation of spiral galaxies
  • in 1929, he discovered the sodium layer, a layer within the Earth's mesosphere of unbound, non-ionized atoms of sodium
  • was responsible for hiring Clyde Tombaugh and supervised the work that led to the discovery of Pluto in 1930

Ideas and Concepts:

Galaxy of the day, via tonight's Origins of the Universe course:

"The Andromeda Galaxy is one of the brightest of any of the Messier objects, making it visible to the naked eye on moonless nights even when viewed from areas with moderate light pollution. Although it appears more than six times as wide as the full Moon when photographed through a larger telescope, only the brighter central region is visible to the naked eye or when viewed using binoculars or a small telescope.

In 1920, the Great Debate between Shapley and Curtis took place, concerning the nature of the Milky Way, spiral nebulae, and the dimensions of the universe. To support his claim that the Great Andromeda Nebula was an external galaxy, Curtis noted the appearance of dark lanes resembling the dust clouds in our own Galaxy, as well as the significant Doppler shift.

Edwin Hubble settled the debate in 1925 when he identified extragalactic Cepheid variable stars (stars that vary between a larger, brighter state and a smaller, denser one) for the first time, which enabled the distance of Great Andromeda Nebula to be determined. His measurement demonstrated conclusively that this feature was not a cluster of stars and gas within our Galaxy, but an entirely separate galaxy located a significant distance from our own.

On January 5, 2015, the following image was released by NASA. Captured with the Hubble Telescope, it is the largest and sharpest image ever taken of the Andromeda galaxy. It is too large to be easily displayed at full resolution and so is best appreciated in all its depth using this zoom tool."
The day the universe got bigger, via tonight's Galaxies and Cosmology class:

"Cepheid variable stars vary between a larger, brighter state and a smaller, denser one in such a way that their luminosity and pulsation make them particularly important as distance indicators for establishing the galactic and extragalactic distance scales.

The discovery by Edward Hubble in 1923 of one particular Cepheid variable star in the Andromeda galaxy altered the course of modern astronomy. He found that the star brightened and faded in a predictable pattern, like a lighthouse beacon, and identified it as V1, a Cepheid variable.

During this time in the early 1900s, most astronomers considered the Milky Way a single island universe of stars, with nothing observable beyond its boundaries. The Andromeda galaxy was cataloged as just one of many faint, fuzzy patches of light astronomers called spiral nebulae.

This special type of star had already been proven to be a reliable distance marker within our galaxy, and so it helped Hubble show that Andromeda was far beyond our galaxy which settled the debate over the status of the spiral nebulae, and made the universe a much bigger place."
From the monumental oversights department, via this morning's Galaxies and Cosmology class: "Einstein failed to predict the expansion of the universe even though this was explicitly contained in his equations and is probably the greatest scientific prediction anyone could make."
Early History of Cosmology
20th Century Developments in Cosmology