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Part 19: Galactic age, evolution, and physics.

These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:

01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
18. Galaxies
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences

19. Galaxies 2 University of Arizona

    • Wetenschap

Part 19: Galactic age, evolution, and physics.

These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:

01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
18. Galaxies
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences

    • video
    Hubble

    Hubble

    Transcript: Edwin Hubble was highly accomplished. A boxer, a Rhodes Scholar, a lawyer, all before turning his attention to astronomy. He joined the Mount Wilson Observatory just before the first World War where he was able to use their new hundred-inch telescope, the Hooker reflector, then the world’s largest. Hubble’s two main achievements in his career were monumental. First he demonstrated that many of the nebulae were distant systems of stars remote from the Milky Way galaxy. At a stroke he expanded the size of the known universe by a factor of hundreds. Second, he established that galaxies had redshifts that indicated the universal expansion, and this fact leads to the idea of the big bang model of the universe. The premier research facility in astronomy, the Hubble Space Telescope, is named after him.

    • 57 sec.
    • video
    Resolving the Nebula

    Resolving the Nebula

    Transcript: The first step in understanding the nature of the nebulae involve resolving the nebulae. As newer, larger telescopes were built near the beginning of the twentieth century astronomers gained powerful tools to break up the diffuse light of the nebulae into the pinpoint light of many stars. Remember that the resolution of a telescope increases with its size, subject to the limitation of the Earth’s atmosphere. In the early twentieth century Edward Fath and other astronomers had noted the pinpoint light that composed the nebulae and, using a similar logic to the idea that the stars are much more distant than the Sun as given by their relative brightnesses and the inverse square law, deduced that if the pinpoint light in the nebulae were related to the starlight of the Milky Way, those stars must be extremely distant, far more than the distance to the edge of the Milky Way galaxy. This evidence, however impressive, is still indirect, and it took Edwin Hubble and his use of Cepheid variables to clench the fact that at least one of the nebulae, the Andromeda nebula, was remote from the Milky Way itself.

    • 1 min.
    • video
    Distance to Andromeda

    Distance to Andromeda

    Transcript: Hubble’s use of Cepheid variables to measure the distance to the Andromeda nebula is sufficiently important in the history of astronomy to study his logic carefully. He started by taking sequential observations on photographic plates over a period of months allowing him to identify variable stars in the Andromeda nebula. He knew that there was a universal period-luminosity relationship for Cepheid variables in the Milky Way. He then identified Cepheids with the same periods near the Sun whose distances were measured by other means and in the Andromeda nebula. These therefore have the same luminosity or absolute magnitude. He measured the apparent brightness difference between the Cepheid variables and the ones in the Milky Way. They were typically a million times fainter. By the inverse square law the M31 Cepheids must be the square root of a million, a thousand times further away. So if the local Cepheid is at a distance of two thousand light years the M31 Cepheid must be a thousand times further away, two million light years.

    • 1 min.
    • video
    Distance Indicators

    Distance Indicators

    Transcript: Any property of a star or galaxy that can be used to measure distance is called a distance indicator. In astronomy the best distance indicators have a clear physical or astrophysical basis and are not purely empirically determined. Within the solar system, the most direct technique possible is radar which uses our own measurement and knowledge of the speed of light and electromagnetic radiation. Also, Kepler’s laws are used within the solar system. To measure nearby stars the geometric method of parallax is used. For more distant stars main sequence fitting can be used. To go to the edge of the Milky Way and beyond we use luminous variable stars whose properties are well understood and related to their luminosities, the RR Lyrae stars and the Cepheid variables. Finally to go to the largest distances beyond the Milky Way the most luminous possible stellar moments are used, the peak brightness of a supernova, in particular Type I supernovae which represent the well regulated process whereby a white dwarf detonates when mass is transferred on it from a more massive member of a binary system.

    • 1 min.
    • video
    Distance Scale

    Distance Scale

    Transcript: The distance scale in astronomy is a set of measurements that define distances all the way from the solar system to the most remote galaxies. Conceptually it’s a pyramid with nearby methods being direct and fairly accurate while the errors accumulate and grow to the point where the measurement of the distance to galaxies is rarely more accurate than ten percent. Why are many techniques needed to establish a distance scale? In part, it’s due to the vastness of space. Any distance indicator that can be found near the Sun must also be found ten thousand times further away to be seen on the other side of the galaxy at which point it’s ten to the eight or a hundred million times fainter. Similarly, a distance indicator that can be seen on the other side of the galaxy must also be seen a thousand times further away to be seen in distant galaxies at which point it’s a million times fainter. Thus nearby distance indicators become too faint to be useful at some point, whereas the most luminous distance indicators are very rare locally, for example supernovae which only occur once every fifty years or so in the entire Milky Way.

    • 1 min.
    • video
    Random Errors in Distance

    Random Errors in Distance

    Transcript: The role of errors is always important in astronomy but in no case more than in the distance scale. Random errors tend to grow as we move away from the Milky Way and even from the solar system. Within the solar system radar gives us accurate measure of the distance to nearby planets with a precision of ten to the minus four percent. The distance to the nearby stars using the parallax technique is accurate to about one percent. However, when we move beyond the Milky Way we are using distance indicators whose physical basis is not always totally reliable and where the data is limited by the brightness of the objects. So the error to the distances of nearby galaxies is usually in the range of five to ten percent, and for most distant galaxies it can be ten or twenty percent.

    • 54 sec.

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