Part 4: Basic concepts of chemistry and physics and how the apply to astronomy.
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:
Astronomy with Chris Impey -
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
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
Newton and Cosmology
Transcript: Newton viewed both time and space as smooth, absolute, and Euclidian. Newton’s gravity law is an inverse square law, so the gravity of every object diminishes with the square of the distance. However it never reaches zero because one over the square of a large number is a very small number but not zero. Newton believed in an infinite universe, which means that in an infinite universe filled with objects, stars or galaxies, the gravity is infinite too. This was a problem for Newton’s theory of gravity and for his understanding of cosmology. He could not solve this problem at the time. Newton also did not understand what was the nature of the force of gravity that could act across the vacuum of space. As he said, “I frame no hypothesis.”
Transcript: The circular velocity is the velocity needed to create an orbit. Circular velocity for the Earth is 7.8 kilometers per second. This is about 17,500 miles per hour, so obviously a very large rocket and a lot of energy is needed to put something in orbit. Circular velocity scales up with the mass of the gravitating object and scales down with the distance from that object.
Transcript: The speed required to completely escape from the gravity of something is called the escape velocity. At the escape velocity the kinetic energy exactly equals the gravitational potential energy, and an object can escape to an infinite distance from the gravity of a large body. Earth’s escape velocity is eleven kilometers per second. The escape velocity is always the square root of two times the circular velocity, about 40 percent larger. Something that escapes the Earth’s gravitational field is still held by the gravity of the sun however. Earth’s circular velocity around the sun is 30 kilometers per second. Square-root two times larger is 42 kilometers per second. Therefore any object or rocket that can be accelerated to 42 kilometers per second can leave the solar system. Four man-made objects or satellites have done so, so far.
Transcript: A low-Earth orbit corresponds to a distance of about 200 kilometers above the Earth’s surface. This is a tiny fraction of the Earth’s diameter but sufficient to be above the entire atmosphere. At this height and at a speed of 7.8 kilometers per second, the orbital time is about 90 minutes. Low-Earth orbit, for example, is the orbit of the Hubble Space Telescope. At the cost of considerably more energy an orbit can be created whose period is 24 hours. In this situation something can hover above one point of the rotating Earth. This is called a geosynchronous orbit, and it is obviously a favored orbit for things such as telecommunications satellites.
Solar System Exploration
Transcript: Public interest in the space program and its cost probably peaked in the late 1960s with the Apollo program. In a series of six launches twelve astronauts set foot on the moon and brought back a few hundred kilograms of moon rocks. The program was cancelled in 1972. Thereafter, NASA turned to exploration of the solar system using unmanned probes. Both the Russians and the Americans sent probes to Venus and Mars, and by the end of the 1970s probes had been sent to explore all the planets of the solar system except Pluto. The result of all this activity was a burst of innovation in the field of planetary science.
Manned Space Flight
Transcript: Space exploration is expensive, and space travel using humans is even more expensive. The high cost almost forces international cooperation. This started in the 1970s with the Apollo-Soyuz program. In the 1980s the United States developed the first reusable spacecraft, the space shuttle. The space shuttle was envisaged originally as something like a truck that could go into space forty or fifty times a year at a moderate cost. The reality has not been so happy. The space shuttle costs each flight fifty or a hundred times more than originally planned and has never gone up more than ten or twelve times a year. Two of the five space shuttles have been catastrophically lost with the astronauts on board. The Mir Space Station built by the Russians degraded so badly that it had to be abandoned. The International Space Station is now underway cooperatively between Europe, the United States, Russia, and Japan, but the cost is making all of those countries reconsider their involvement.
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4. 7. Only three men have died in space, and the estimated price for a commercial mission to Mars was cited as one billion by SpaceX if posed as a challenge to contributors to keep costs down and obtain tech laterally. The risks of dying in space are significantly lower than your risk of dying from a car crash, or from having livestock fall from the sky and strike you dead; which actually happens far more often than you would guess (google it if you have some spare time and wish to have your mind boggled).