Part 13: Nuclear forces and interactions as well as solar features and processes.
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
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
Darwin and Kelvin
Transcript: Chemical energy cannot power the Sun, so what is the energy source? Inspired by an idea by the German physicist Hermann von Helmholtz the English physicist Lord Kelvin explored the idea of gravitational contraction. In this mechanism the Sun is slowly shrinking and gravitational potential energy is being converted into heat energy which then radiates out into space. In his estimate the Sun might last a couple of hundred million years with this mechanism. It sounds like a long time, but by the mid-nineteenth century the debate about the age of the Sun began to collide with the debate about the age of the Earth. Most people assumed they formed at the same time. Charles Darwin’s theory of natural selection seemed to require many millions of years for the diversity of species to be achieved from simple origins. In the nineteenth century in England it was common to have scientific debates carried out in public for a public audience and scientists as well. Darwin had debated Wilberforce on the subject of natural selection and by general acclaim had won the debate. In 1871 Lord Kelvin debated Thomas Huxley who was standing in for Darwin on the issue of the age of the Sun and the age of the Earth. Darwin had estimated that the age of the Earth needed to be many hundreds of millions of years, perhaps billions of years to explain the diversity of species, but Kelvin said the Sun could be no older than half a billion years based on gravitational contraction. Darwin died without knowing whether the Earth could be old enough for his mechanism to work.
Energy from Atomic Nuclei
Transcript: Physicists in the nineteenth century made various estimates of the age of the Sun, but they were fundamentally unaware of the most efficient energy source known. Early in the twentieth century physicists Rutherford and Becquerel began a systematic study of the phenomenon of radioactivity, a situation where atoms spontaneously emit both particles and radiation. Rutherford for example sealed a small amount of a radioactive substance in a tube that contained a pure vacuum. He returned months later to find that the tube contained helium gas and that the chemical properties of the radioactive substance had changed. Here was proof both that the atomic nucleus can emit energy and that chemicals can change fundamentally due to radioactive processes. The atomic nucleus could be transformed, and it could emit energy.
Transcript: Radioactive decay is a phenomenon of the atomic nucleus. In these processes an element changes its chemical properties, that is its atomic number, by the emission of particles and or radiation. Radioactivity is a random process. It’s impossible to predict exactly when a particular radioactive decay will occur. However, in a collection of atoms there is a well defined half-life or time that it takes one starting point, that is the parent isotope, to turn into the decayed product or daughter isotope. Physicists early on did not understand the fundamental nature of the radioactive process, and they categorized the three types of decay as alpha decay, beta decay, and gamma decay.
Alpha, Beta, and Gamma Decay
Transcript: The three basic types of radioactive decay are called alpha, beta, and gamma decay. In the alpha process an atom spontaneously emits a helium nucleus. Helium nucleus contains two protons and two neutrons so alpha decay reduces the atomic number by two. In beta decay a neutron decays into a proton, an electron, and a neutrino. A neutron is only stable when bound in an atomic nucleus. Free neutrons will decay radioactively. The final type of emission is called gamma radiation. Gamma rays are high energy photons released spontaneously by radioactive atoms.
Transcript: Working early in the twentieth century physicist Marie Curie was able to show that radioactive processes released millions of times more energy per atom than any chemical process known. Marie Curie was a pioneer. With her husband she was the first to isolate a radioactive element. She was the first female professor in the six hundred year history of the Sorbonne. She was the first person ever to win two Nobel Prizes; however Marie and many others who worked on radioactivity paid heavily for being pioneers. Unaware of the damaging effects of radiation on human skin and tissue they died from radioactive poisoning.
Mass, Energy Conservation
Transcript: The nucleus of the atom contains a prodigious potential energy source. Mass and energy are related by Einstein’s famous equation E = mc2. Since c is a very large number, three hundred thousand kilometers per second, c2 is an even larger number. So a tiny amount of mass is equivalent to a huge amount of energy. When you plug the numbers in you can see how dramatic this is. The mass-energy equivalent to the tip of a pencil lead is sufficient to run a family home for a day. The mass-energy equivalent to an adult person is sufficient to provide ten to the nineteen Joules which is the energy requirement of the United States for a year. The inefficiency of chemical energy is also clear. The Saturn V rocket that took astronauts to the moon had ninety percent of its mass in the form of fuel that had to be burned up to launch the projectile. Ten grams of mass energy would have provided the same energy source. For a final every day example, consider a quarter pounder hamburger. This provides the average person who eats it two hundred and fifty calories or a million Joules, but the mass-energy in that amount of material is ten to the sixteen Joules. Thus we only extract one part in ten to ten of the total energy of the hamburger in the form of chemical energy.