

Radio Astronomy: Observing the Invisible Universe
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Episodi
S1 E1 - Radio Astronomy and the Invisible Universe
9 novembre 201731minEven on the clearest, darkest night you cannot see more than five percent of the light from our home galaxy, the Milky Way, because of the blockage of light by dust. Fortunately, the 20th century brought us radio astronomy, the study of radio waves that travel through the dust, opening our "eyes" to a universe we had never imagined.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E2 - Thermal Radio Emission: The Planets
9 novembre 201729minTake a tour of our neighboring planets via their radio emissions and learn how scientists infer their temperatures and energy sources. You'll be shocked by the difference between their images in reflected sunlight - the images we're familiar with - and their appearance when we "see" the radio energy they emit on their own.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E3 - The Birth of Radio Astronomy
9 novembre 201730minWhen young engineer Karl Jansky was tasked to find natural radio sources that could interfere with commercial transatlantic radio communications, radio astronomy was born. His work led to the discovery of synchrotron radiation. But it would be decades before scientists understood what these earliest radio astronomers had detected - cosmic rays and magnetic fields.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E4 - The Discovery of Interstellar Hydrogen
9 novembre 201728minNot long after the birth of radio astronomy, a Dutch student used what was then known about the physics of atoms to determine that if hydrogen existed in interstellar space, it would produce a specific spectral line at radio wavelengths. In 1951, the line was detected at 21 cm, exactly as predicted. At that moment, our understanding of the universe forever changed.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E5 - Radio Telescopes and How They Work
9 novembre 201734minRadio telescopes are so large because radio waves contain such a small amount of energy. For example, the signal from a standard cell phone measured one kilometer away is five million billion times stronger than the radio signals received from a bright quasar. Learn how each of these fascinating instruments is designed to meet a specific scientific goal.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E6 - Mapping the Hydrogen Sky
9 novembre 201731minBefore there were stars and planets, before there were galaxies, there was hydrogen - and we still have more hydrogen today than any other element. Understanding the quantum physics of this simplest atomic structure, and using the Doppler shift and models of differential rotation in the Milky Way, astronomers have made myriad astounding discoveries about the universe. It all starts with hydrogen.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E7 - Tour of the Green Bank Observatory
9 novembre 201729minThe Green Bank Observatory is located within the 13,000-acre National Radio Quiet Zone straddling the border of Virginia and West Virginia. Come tour this fascinating facility where astronomers discovered radiation belts around Jupiter, the black hole at the center of our galaxy, and the first known interstellar organic molecule, and began the search for extra-terrestrial life.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E8 - Tour of the Green Bank Telescope
9 novembre 201731minAt 17 million pounds, and with more than 2,000 surface panels that can be repositioned in real time, this telescope is one of the largest moveable, land-based objects ever built. The dish could contain two side-by-side football fields, but when its panels are brought into focus, the surface has errors no larger than the thickness of a business card. Welcome to this rare insider's view.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E9 - Hydrogen and the Structure of Galaxies
9 novembre 201732minUsing the laws of physics and electromagnetic radiation, astronomers can "weigh" a galaxy by studying the distribution of its rotating hydrogen. But when they do this, it soon becomes clear something is very wrong: A huge proportion of the galaxy's mass has simply gone missing. Welcome to the topsy-turvy world of dark matter - which we now believe accounts for 90 percent of our own Milky Way.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E10 - Pulsars: Clocks in Space
9 novembre 201731minIn the mid-1960s, astronomers discovered signals with predictable periodicity but no known source. In case these signals indicated extraterrestrial life, they were initially labeled LGM, Little Green Men. But research revealed the source of the pulsing radiation to be neutron stars.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E11 - Pulsars and Gravity
9 novembre 201731minA pulsar's spin begins with its birth in a supernova and can be altered by transfer of mass from a companion star. Learn how pulsars, these precise interstellar clocks, are used to confirm Einstein's prediction of gravitational waves by observations of a double-neutron-star system, and how we pull the pulsar signal out of the noise.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E12 - Pulsars and the 300-Foot Telescope
9 novembre 201732minHumans constantly use radio transmission these days, for everything from military communications to garage-door openers. How can scientists determine which signals come from Earth and which come from space? Learn how the 300-foot telescope was built quickly and cheaply. It ended up studying pulsars and hydrogen in distant galaxies, and made the case for dark matter.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E13 - The Big Bang: The Oldest Radio Waves
9 novembre 201731minLearn about techniques to separate signals originating in receivers from signals originating from outer space. Using a unique antenna located in New Jersey, we'll see how two radio astronomers with curiosity, persistence, and some manual labor, detected the faint radio signals from the big bang, the oldest electromagnetic radiation that can be detected.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E14 - H II Regions and the Birth of Stars
9 novembre 201731minHave you ever looked up to Orion on a dark winter's night and noticed a fuzzy patch near the center of the constellation? You're looking at the Orion nebula, a "nursery" where stars are born every year. Learn why ionization occurs in these H II regions and how this hot plasma produces some of the most beautiful objects in the sky.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E15 - Supernovas and the Death of Stars
9 novembre 201732minChances are you would agree with astronomers that gravity is the single most important force or event shaping the world as you know it. But the second most important? That would be supernovas, and nothing you know would be here without them. Learn how super-massive stars can explode at the end of their lives, releasing energy that outshines 10 billion Suns.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E16 - Radio Stars and Early Interferometers
9 novembre 201730minWhen radio astronomers discovered a sky full of small radio sources of unknown origin, they built telescopes using multiple antennas to try to understand them. Learn how and why interferometers were developed and how they have helped astronomers study quasars - those bright, star-like objects that scientists now know only occur in galaxies whose gas is falling into a supermassive black hole.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E17 - Radio Source Counts
9 novembre 201731minRadio source counts have led to great discoveries about the universe, even though each individual radio source isn't fully understood. Between massive black holes and starbursts, scientists relying in part on astronomical surveys now believe galaxies can have different evolutionary tracks and histories. And the universe itself? It seems to be not only evolving, but evolving through stages.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E18 - Active Galactic Nuclei and the VLA
9 novembre 201731minThe need for a new generation of radio interferometers to untangle extragalactic radio sources led to the development of the Very Large Array (VLA) in New Mexico. With its twenty-seven radio antennas in a Y-shaped configuration, it gives both high sensitivity and high angular resolution. The VLA provided a deeper and clearer look at galaxies than ever before, and the results were astonishing.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E19 - A Telescope as Big as the Earth
9 novembre 201731minLearn how astronomers use very-long-baseline interferometry (VLBI) with telescopes thousands of miles apart to essentially create a radio telescope as big as the Earth. With VLBI, scientists not only look deep into galactic centers, study cosmic radio sources, and weigh black holes, but also more accurately tell time, study plate tectonics, and more - right here on planet Earth.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E20 - Galaxies and Their Gas
9 novembre 201731minIn visible light, scientists had described galaxies as "island universes." But since the advent of radio astronomy, we've seen galaxies connected by streams of neutral hydrogen, interacting with and ripping the gasses from each other. Now astronomers have learned hat these strong environmental interactions are not a secondary feature - they are key to a galaxy's basic structure and appearance.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E21 - Interstellar Molecular Clouds
9 novembre 201733minIn the late 1960s, interstellar ammonia and water vapor were detected. Soon came formaldehyde, carbon monoxide, and the discovery of giant molecular clouds where we now know stars and planets are formed. With improvements in radio astronomy technology, today's scientists can watch the process of star formation in other systems. The initial results are stunning.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E22 - Star Formation and ALMA
9 novembre 201733minWith an array of 66 radio antennas located in the high Chilean desert above much of the earth's atmosphere, the Atacama Large Millimeter/submillimeter Array (ALMA) is a radio telescope tuned to the higher frequencies of radio waves. Designed to examine some of the most distant and ancient galaxies ever seen, ALMA has not only revealed new stars in the making, but planetary systems as well.Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E23 - Interstellar Chemistry and Life
9 novembre 201733minInterstellar clouds favor formation of carbon-based molecules over any other kind - not at all what statistical models predicted. In fact, interstellar clouds contain a profusion of chemicals similar to those that occur naturally on Earth. If planets are formed in this rich soup of organic molecules, is it possible life does not have to start from scratch on each planet?Periodo d’uso gratuito di The Great Courses Signature Collection o acquistoS1 E24 - The Future of Radio Astronomy
9 novembre 201737minLearn about the newest radio telescopes and the exhilarating questions they plan to address: Did life begin in space? What is dark matter? And a new question that has just arisen in the past few years: What are fast radio bursts? No matter how powerful these new telescopes are, radio astronomers will continue pushing the limits to tell us more and more about the universe that is our home.Periodo d’uso gratuito di The Great Courses Signature Collection o acquisto