1: Radio Astronomy and the Invisible Universe

• Even 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....

2: Thermal Radio Emission: The Planets

• Take 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....

3: The Birth of Radio Astronomy

• When 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, and that of backyard astronomer Grote Reber, 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 magnet...

4: The Discovery of Interstellar Hydrogen

• Not 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....

5: Radio Telescopes and How They Work

• Radio 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-accounting for their wide variation in form ...

6: Mapping the Hydrogen Sky

• Before 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....

7: Tour of the Green Bank Observatory

• The 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....

8: Tour of the Green Bank Telescope

• At 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....

9: Hydrogen and the Structure of Galaxies

• Using 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 a whopping 90 percent of our own Milky ...

10: Pulsars: Clocks in Space

• In 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. Learn how a star with a diameter of only a few kilometers and a mass similar to that of our Sun can spin around hund...

11: Pulsars and Gravity

• A 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....

12: Pulsars and the 300-Foot Telescope

• Humans 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, located in two radio quiet zones, was built quickly and cheaply. It ended up studying pulsars and hydrogen in distant galaxies, and made the case for dar...

13: The Big Bang: The Oldest Radio Waves

• Learn 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. It tells us of conditions when the uni...

14: H II Regions and the Birth of Stars

• Have 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....

15: Supernovas and the Death of Stars

• Chances 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....

16: Radio Stars and Early Interferometers

• When 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 massively bright, star-like objects that scientists now know only occur in galaxies whose gas is falling into a supermassive black hol...

17: Radio Source Counts

• Radio 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....

18: Active Galactic Nuclei and the VLA

• The 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....

19: A Telescope as Big as the Earth

• Learn 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....

20: Galaxies and Their Gas

• In 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 come to understand that these strong environmental interactions are not a secondary feature-they are key to a galaxy's basic structure and appea...

21: Interstellar Molecular Clouds

• In 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....

22: Star Formation and ALMA

• With 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....

23: Interstellar Chemistry and Life

• Interstellar 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?...

24: The Future of Radio Astronomy

• Learn 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....

25: Three New Discoveries

• Imagine being there for the discovery of the moons of Jupiter, the Theory of Relativity, or the first glimpse of exoplanets. One of the greatest things about studying a subject such as radio astronomy is that new discoveries are constantly being made and our professors want you to be part of it.

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