Part 5: Basic concepts in optics, particle physics, and thermodynamics.
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
Transcript: There are three basic modes of heat transfer or ways that energy can be carried from a higher temperature material to lower temperature material. One is conduction which is heat transfer by tiny microscopic motions of the atoms or molecules. Conduction can occur in solids and liquids but not gases because the density is too low. Convection is the large wholesale motion of masses of material, and it can occur most effectively in liquids and gases, although conduction does occur in the high temperature molten magma of the Earth itself. The third mode of energy transfer is radiation. This can operate through the vacuum of space.
Transcript: Convection is heat transfer through the motion of masses of material. It’s a very efficient way to transfer a thermal energy. If you poured boiling water into a bath and just waited, the extra kinetic motion of the molecules in the boiling water would eventually diffuse through the bath, heating up the bath, but if you swirled around the water with your hand the bath would heat up more quickly. The swirling of the water corresponds to convection. Similarly, when you boil a pan of water, as the water starts to boil motion is being carried by diffusion from the bottom of the pan towards the top of the pan. Eventually that process is not efficient enough, and the water starts to move in rolling motions carrying heat from the bottom to the top by convection. A similar process works within the Earth’s atmosphere due to the heating effect of the ground causing churning motions of air packets moving up as they are hot and down as they become cooler.
Transcript: Radiation is another mode of heat transfer or way to move energy from one place to another. Every object that has a temperature emits thermal radiation. Unlike the case of convection or conduction, radiation can occur through the vacuum of space. It is the Sun’s radiation that stops the Earth from being in a deep freeze. Radiation is one of the most fundamentally important concepts in astronomy.
Transcript: Newton was the first to describe the components of radiation emitted by the sun. He took the sun’s light and dispersed it in wavelength with a prism and created the visible spectrum. The visible spectrum runs through the colors of the rainbow: red, orange, yellow, green, blue, indigo, violet, often creating the mnemonic Roy G. Biv. This sequence from red to blue is also a sequence of decreasing wavelength and increasing frequency.
Transcript: The visible spectrum is just one slice of a much larger range of radiations. Nearly two hundred years ago two scientists demonstrated this. Around the year 1800, William Herschel took a spectrum of sunlight and placed a thermometer beyond the red end of the spectrum. The temperature rose, demonstrating that energy existed beyond the visible end of the spectrum. A couple of years later, German chemist Johann Ritter placed a sheet of paper soaked in silver-chloride beyond the blue end of a visible spectrum of sunlight. The paper darkened, also demonstrating that energy existed beyond the blue end of the spectrum. In this way we had proof of infrared radiations beyond the red end of the spectrum and ultraviolet radiation beyond the violet end of the spectrum.
Transcript: We all have an idea of the concepts of hot and cold, but what aspect of matter does temperature really measure? Temperature measures the microscopic motions of atoms or molecules in any substance. The higher the temperature, the faster the random microscopic motions. This is the scientific definition of temperature that applies on the microscopic scale and the macroscopic scale. Note however that thermal energy and temperature are not the same thing. A drop of boiling water has the same temperature as a cup of boiling water, but the cup of boiling water clearly has more thermal energy. Thermal energy has to do with the amount of material whereas temperature itself as a concept relates only to the microscopic motion of the atoms or molecules.