Understanding the Universe: An Introduction to Astronomy, 2nd Edition

Course No. 1810
Professor Alex Filippenko, Ph.D.
University of California, Berkeley
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Course No. 1810
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What Will You Learn?

  • numbers From wormholes to quantum mechanics to dark matter, enjoy a comprehensive look at the fundamentals of astrophysics.
  • numbers Make sense of the complexities of astrophysics with the help of thousands of easy-to-understand graphics and animations.
  • numbers Witness the breathtaking range of objects in the Universe with the aid of hundreds of images from the Hubble Telescope.
  • numbers Learn about the growing number of unmanned missions designed to explore little-known features of our solar system.

Course Overview

This visually rich course is designed to provide a nontechnical description of modern astronomy, including the structure and evolution of planets, stars, galaxies, and the Universe as a whole. It includes almost all of the material in my first two astronomy courses for The Teaching Company, produced in 1998 and 2003, but with a large number of new images, diagrams, and animations. The discoveries reported in the 2003 course are integrated throughout these new lectures, and more recent findings (through mid-2006) are included, as well. Much has happened in astronomy during the past few years; we will discuss the most exciting and important advances.

Astronomical objects have been explored with breathtaking data obtained by the Hubble Space Telescope, the Chandra X-Ray Observatory, the Keck 10-meter telescopes, planetary probes, and other modern instruments. We will explore amazing phenomena, such as quasars, exploding stars, neutron stars, and black holes, and we will see how they increase our understanding of the physical principles of nature. We will also investigate recent newsworthy topics, such as the Cassini mission to Saturn, evidence for liquid water on ancient Mars, the discovery of many small bodies beyond Neptune in our Solar System, the detection of numerous planets around other stars, the nonzero mass of ghostly neutrinos, enormously powerful gamma-ray bursts, the conclusive evidence for a supermassive black hole in the center of our Milky Way Galaxy, the determination of the age of the Universe, the discovery of a long-range repulsive effect accelerating the expansion of the Universe, and progress in the unification of nature’s fundamental forces. Scientifically reasonable speculations regarding the birth of the Universe, the possibility of multiple universes, and the probability of extraterrestrial life are also included.

This course concentrates on the most exciting aspects of our fantastic Universe and on the methods astronomers have used to develop an understanding of it. The lectures present, in clear and simple terms, explanations of how the Universe “works,” as well as the interrelationships among its components. Reliance on basic mathematics and physics is minimal but appropriate in some sections to deepen the interested viewer’s quantitative understanding of the material.

The course is divided into three major sections, each of which consists of several units. (These major sections are called “parts” during the lectures, but they are not to be confused with the eight 12-lecture “parts” used in packaging the lectures.)

There are 24 lectures in Section 1, entitled “Observing the Heavens.” The first unit, “Celestial Sights for Everyone,” describes simple daytime and nighttime observations that you can make to better appreciate the sky and what it contains. Various commonly observed phenomena, such as seasons, lunar phases, and eclipses, are also discussed. The second unit, “The Early History of Astronomy,” covers the study of astronomy from the ancient Greeks through Newton, including the transition from geocentric (Earth-centered) to heliocentric (Sun-centered) models of the Universe. In the third unit, “Basic Concepts and Tools,” we provide an overview of distance and time scales in the Universe to put our discussions in perspective. Because the study of light is of central importance to astronomy, we spend several lectures explaining its physical nature and utility. Modern telescopes, the main instruments used by astronomers, are also described.

Section 2, “The Contents of the Universe,” consists of 46 lectures in 5 units. In the first unit, “Our Solar System,” we discuss the major constituents of our own planetary system, including the Sun, planets and their moons, comets, asteroids, and Kuiper-belt objects. The discovery of a distant body larger than Pluto and the subsequent, highly controversial demotion of Pluto from planetary status made headlines worldwide. The formation of other stars and planetary systems, as well as the discovery of such extrasolar planets, is the subject of the second unit, “Other Planetary Systems.” During the past decade, about 200 planets have been found orbiting other stars, making this one of the most exciting areas of modern astronomy. The search for extraterrestrial life is also described.

In the third unit of Section 2, “Stars and Their Lives,” we learn about the properties of other stars and the various observations needed to deduce them. Nuclear reactions, the source of energy from the stars, are described, as well. We examine how stars eventually become red giants, subsequently shedding their outer layers to end up as dense white dwarfs, retired stars. The explosive fates of some rare types of stars are the subject of the fourth unit, “Stellar Explosions and Black Holes,” and we explain how the heavy elements necessary for life are created. Bizarre stellar remnants include neutron stars and black holes, the realm of Einstein’s general theory of relativity. We continue our exploration of black holes with such phenomena as black-hole evaporation and powerful gamma-ray bursts, as well as speculations that black holes are gateways to other universes. In the fifth unit, “The Milky Way and Other Galaxies,” we extend our explorations to the giant collections of stars called galaxies, along the way examining evidence for mysterious dark matter.

Section 3, “Cosmology: The Universe as a Whole,” comprises the final 26 lectures of the course in 3 units. The first unit, “Cosmic Expansion and Distant Galaxies,” introduces the expansion of the Universe and shows how it is used to study the evolution of galaxies. We discuss active galaxies and quasars, in which matter is inferred to be falling into a central, supermassive black hole. In the second unit, “The Structure and Evolution of the Universe,” aspects of the Universe, such as its age, geometry, and possible fate, are considered. We examine evidence for the stunning conclusion that the expansion of the Universe is currently accelerating. We also describe the cosmic microwave background radiation—the generally uniform afterglow of the Big Bang—as well as the tiny irregularities that reveal the presence of early density variations from which all of the large-scale structure of the Universe subsequently formed. The nature of dark energy accelerating the Universe is explored in terms of modern attempts to unify forces, such as string theory.

In the third and final unit, “The Birth of the Cosmos, and Other Frontiers,” we examine the very early history of the Universe, showing how the lightest elements formed during a phase of primordial nucleosynthesis. The recognition of several troubling problems with the standard Big Bang theory led to a magnificent refinement—an inflationary epoch of expansion that lasted only a tiny fraction of a second. The possible connection between inflation and the currently accelerating expansion of space is also discussed. We then consider very speculative ideas regarding the birth of the Universe and the hypothesis of multiple universes. We end, in the last lecture, on a philosophical note, with some reflections on intelligent life in the cosmos and of our place in the grand scheme of things.

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96 lectures
 |  Average 31 minutes each
  • 1
    A Grand Tour of the Cosmos
    You embark on a fantastic voyage throughout the Universe, starting in this lecture with a whirlwind tour of the course, which extends from phenomena in Earth's atmosphere to events at the farthest reaches of space and time. x
  • 2
    The Rainbow Connection
    The daytime sky contains intriguing natural sights that offer a colorful introduction to astronomy. One such phenomenon is the rainbow. This lecture examines how a rainbow is created and how it appears under different circumstances. x
  • 3
    Sunrise, Sunset
    Continuing the study of the daytime sky, this lecture examines phenomena associated with sunrise and sunset, including the elusive green flash, Buddha's rays, and Earth's own shadow at sunset. x
  • 4
    Bright Objects in the Night Sky
    Many objects in the night sky can be enjoyed with the naked eye, even from the city. These include several famous constellations, bright stars, planets, and satellites such as the International Space Station. x
  • 5
    Fainter Phenomena in the Night Sky
    Far from city lights, the night sky becomes spectacular and includes such sights as the Milky Way, the Magellanic Clouds, zodiacal light, and comets. Though not technically "celestial," auroras are also wondrous spectacles. x
  • 6
    Our Sky through Binoculars and Telescopes
    A relatively inexpensive telescope and even a simple pair of binoculars greatly increase the number of celestial objects you can study, such as the craters on the Moon, the Orion Nebula, and the Andromeda Galaxy. x
  • 7
    The Celestial Sphere
    As Earth rotates on its axis and orbits the Sun, the night sky changes over a 24-hour period, as well as throughout the year. This lecture explains how to locate celestial bodies and why the sky appears different from place to place. x
  • 8
    The Reason for the Seasons
    Contrary to popular belief, the seasons are not caused by changes in the distance between Earth and the Sun over the course of a year. Instead, the tilt of Earth's axis of spin relative to the axis of its orbital plane produces seasons. x
  • 9
    Lunar Phases and Eerie Lunar Eclipses
    Lunar phases occur as the Moon orbits Earth, changing the viewing perspective of the Moon's illuminated hemisphere. Lunar eclipses take place when Earth, the Sun, and Moon are almost exactly aligned. x
  • 10
    Glorious Total Solar Eclipses
    Total solar eclipses are stunning celestial sights, which occur when the Moon comes between Earth and the Sun, totally blocking the Sun for a small portion of the Earth. These rare events reveal beautiful and thrilling phenomena. x
  • 11
    More Eclipse Tales
    Solar eclipses also come in annular and hybrid varieties, reflecting the varying distance of the Moon from Earth. A famous total solar eclipse in 1919 provided observational evidence for Einstein's general theory of relativity. x
  • 12
    Early Studies of the Solar System
    Astronomy has its roots in the ancient civilizations of Mesopotamia, Babylon, India, Egypt, and China. The Greeks in particular developed sophisticated and sometimes surprisingly accurate theories of the nature of the heavens. x
  • 13
    The Geocentric Universe
    The Greek philosopher Aristotle concluded that Earth is stationary at the center of the Universe, surrounded by 55 nested spheres. Ptolemy elaborated this geocentric model into a system that held sway for nearly 1,500 years. x
  • 14
    Galileo and the Copernican Revolution
    In 1543, Copernicus proposed a heliocentric system, in which Earth and other planets orbit the Sun, which is at the center of the Universe. In the early 1600s Galileo provided strong evidence for this model with the newly invented telescope. x
  • 15
    Refinements to the Heliocentric Model
    This lecture explores the refinements in the Copernican model made possible by Tycho's extremely accurate measurements of planetary positions, which were analyzed by Kepler to produce his laws of planetary motion. x
  • 16
    On the Shoulders of Giants
    According to legend, Newton saw a falling apple and realized that the force that pulled it toward Earth also pulled on the Moon, keeping it in its orbit. Building on the work of Kepler and Galileo, he revolutionized astronomy with his law of universal gravitation and laws of motion. x
  • 17
    Surveying Space and Time
    Observations of the transit of Venus across the face of the Sun in the 18th century helped determine the scale of the Solar System. In the wider Universe, distances are so vast that the finite speed of light means we are literally looking back in time. x
  • 18
    Scale Models of the Universe
    The best way to understand the size of the Universe is to investigate it in a series of steps, each 10 times larger or smaller than the one preceding. In this way, you explore the cosmos from the smallest to the largest scale. x
  • 19
    Light—The Supreme Informant
    Astronomers obtain most of their information through the analysis of light. This lecture introduces the electromagnetic spectrum and the technique of spectroscopy, in which light is dispersed into its component colors, as in a rainbow. x
  • 20
    The Wave-Particle Duality of Light
    Delving deeper into the nature of light, you explore the strange duality between electromagnetic waves (light waves) and particles (photons), which is a fundamental feature of quantum theory. x
  • 21
    The Colors of Stars
    The surface temperature of a star determines its apparent color. The hottest stars are bluish in color, and the coldest stars are reddish; stars at intermediate temperatures appear white. The Sun is a white star. x
  • 22
    The Fingerprints of Atoms
    Electrons jumping between different energy levels in atoms emit and absorb photons in a characteristic way for each element. Thus, astronomers can use the light from distant objects to deduce their chemical compositions. x
  • 23
    Modern Telescopes
    Today's telescopes are designed to provide huge light-gathering mirrors at relatively low cost. The mirrors focus light from distant objects onto sensitive electronic detectors that are far more efficient than traditional photographic film. x
  • 24
    A Better Set of Eyes
    This lecture looks at radio telescopes, adaptive optics for ground-based infrared telescopes, and NASA's Great Observatories, which include the Hubble Space Telescope, Chandra X-Ray Observatory, and Spitzer Space Telescope. x
  • 25
    Our Sun, the Nearest Star
    Beginning a sequence of lectures on the Solar System, you start with the Sun, which you explore from the interior to the surface. Sunspots are cooler regions associated with strong magnetic fields, and violent eruptions blast solar material into space. x
  • 26
    The Earth, Third Rock from the Sun
    Earth is one of the four innermost, or terrestrial, planets; the others are Mercury, Venus, and Mars. All are relatively small, rocky, and dense. This lecture examines Earth's structure, properties, and the forces that affect it. x
  • 27
    Our Moon, Earth's Nearest Neighbor
    This lecture covers the wealth of knowledge about the Moon, a heavily cratered world with extensive lava-filled basins on the Earth-facing side and yet few such features on the far side—which is not perpetually dark. x
  • 28
    Mercury and Venus
    Though broadly similar to Earth, Mercury and Venus differ in detail. Mercury has a negligible atmosphere and is heavily cratered. Venus has an incredibly thick atmosphere and suffers from an extreme greenhouse effect that makes it intensely hot. x
  • 29
    Of Mars and Martians
    Recent missions to Mars provide evidence for an early water-rich era that may have fostered primitive life. Today, Mars is a cold, apparently lifeless world. Evidence for fossil life in a Martian meteorite remains controversial. x
  • 30
    Jupiter and Its Amazing Moons
    Beyond Mars lie the four gas giants: Jupiter, Saturn, Uranus, and Neptune. Jupiter is the Solar System's largest planet by far. Its moons include Io, which is volcanically active, and Europa, which may have an ocean of liquid water below its frozen surface. x
  • 31
    Magnificent Saturn
    Best known for its extensive ring system, Saturn has come into focus recently thanks to the Cassini spacecraft, which landed a probe on Saturn's largest moon, Titan; and also discovered evidence of liquid water on the moon Enceladus. x
  • 32
    Uranus and Neptune, the Small Giants
    Though less massive than Jupiter and Saturn, Uranus and Neptune are similar in that they consist mostly of hydrogen and helium. Both have bizarre magnetic fields that are highly tilted relative to the planet's rotation axis and offset from the planet's center. x
  • 33
    Pluto and Its Cousins
    Discovered in 1930, Pluto was long considered a planet. However, the detection of more and more objects in the same region strongly suggests that it is a member of a reservoir of comet-like bodies in the Kuiper belt. x
  • 34
    Asteroids and Dwarf Planets
    Under a new definition adopted in 2006, planets are more narrowly defined and a new class called dwarf planets has been created, which includes Pluto, Eris (a Kuiper-belt object larger than Pluto), and Ceres (the largest asteroid). x
  • 35
    Comets—Gorgeous Primordial Snowballs
    Comets are "dirty snowballs" from beyond the orbit of Neptune. As they approach the Sun, they begin to evaporate and produce gaseous tails. In 2005, a space probe impacted Comet Tempel 1, revealing the nature of its interior. x
  • 36
    Catastrophic Collisions
    Comets and asteroids have struck Earth throughout its history. One such collision 65 million years ago probably caused the extinction of the dinosaurs. Astronomers now search for asteroids that could be a potential threat to Earth. x
  • 37
    The Formation of Planetary Systems
    Planets form inside a rotating cloud of dust and gas, which flattens as it contracts. At the center, the temperature is high enough to create a star; farther from the center, leftover material collects into planets. x
  • 38
    The Quest for Other Planetary Systems
    In 1995, the first extra-solar planet was discovered around a Sun-like star. Since then, about 200 have been found. The easiest to detect are those with large masses, close to their host stars, and with brief orbital periods. x
  • 39
    Extra-Solar Planets Galore!
    Because extra-solar planets are too dim to be seen directly, they are detected using a variety of ingenious techniques. Two examples: Minute variations in a star's spectrum and tiny changes in its brightness can signal the presence of planets. x
  • 40
    Life Beyond the Earth
    The recent discovery of extra-solar planets rekindles the age-old question of whether there is life beyond Earth. This lecture examines the possibility of rudimentary life on other planets and moons in the Solar System. x
  • 41
    The Search for Extraterrestrials
    Are there intelligent extraterrestrials elsewhere in our Galaxy? One way to search is to scan the radio spectrum for evidence of their electronic signals. The Drake equation suggests ways to estimate their prevalence. x
  • 42
    Special Relativity and Interstellar Travel
    Are interstellar voyages possible within a single human lifetime? According to Einstein's special theory of relativity, the answer is "yes" in principle but "no" in practice, given current technology. You explore the reasons for both answers. x
  • 43
    Stars—Distant Suns
    A voyage to another star would require exact information on distances and properties of the stars. This lecture shows how astronomers measure the distance to nearby stars and how they determine their surface temperatures, which are the basis for stellar classification. x
  • 44
    The Intrinsic Brightnesses of Stars
    Apparent brightness is the observed brightness of a star. Because stars are at different distances, astronomers need a standard reference by which to compare stars in absolute terms, as if they're all at the same distance: This standard is called intrinsic brightness, or luminosity. x
  • 45
    The Diverse Sizes of Stars
    This lecture discusses the Hertzsprung-Russell diagram, a plot of stellar surface temperature versus luminosity that contains a wealth of information. Stars spend most of their existence on the diagram's well-defined main sequence; outliers include supergiants and white dwarfs. x
  • 46
    Binary Stars and Stellar Masses
    Many stars are members of binary systems, in which two stars orbit a common center of mass. Our best estimates of how much mass stars have come from observations of binaries. We find that massive stars have far shorter lives than low-mass stars. x
  • 47
    Star Clusters, Ages, and Remote Distances
    Star clusters are gravitationally bound groups of stars that are all about the same age and the same distance from Earth. Astronomers can determine the approximate ages of clusters. This lecture also explains how the distance of extremely remote stars is found. x
  • 48
    How Stars Shine—Nature's Nuclear Reactors
    When the central temperature of a contracting cloud of gas grows sufficiently high, it becomes a star—a gigantic, controlled, thermonuclear reactor, fusing hydrogen into helium and maintaining a constant luminosity and size. x
  • 49
    Solar Neutrinos—Probes of the Sun's Core
    Physicists had long assumed that nuclear fusion occurred in the Sun's core, though without a way to physically measure or observe this. Ghostly particles called neutrinos provide direct evidence of events in the Sun's nuclear furnace. x
  • 50
    Brown Dwarfs and Free-Floating Planets
    Brown dwarfs are low-mass objects whose dim glow is caused by slow gravitational contraction and the fusion of deuterium, a heavier but far less abundant isotope of hydrogen. Free-floating planets have even less mass than brown dwarfs and are not associated with any star. x
  • 51
    Our Sun's Brilliant Future
    As it gradually uses up the hydrogen in its core, fusing it to helium, the Sun will expand to form a red giant star. Through a series of relatively nonviolent eruptions, it will expel its outer layers of gas, producing a beautiful, glowing nebula around the dying core. x
  • 52
    White Dwarfs and Nova Eruptions
    The burned out Sun will eventually contract into a white dwarf. This is the fate of all stars between roughly 0.08 and 8 solar masses. A white dwarf in a binary system may steal matter from its companion star and flare up in an eruption called a nova. x
  • 53
    Exploding Stars—Celestial Fireworks!
    A few stars end their lives with cataclysmic explosions, expelling gas at huge speeds. At its peak, such a supernova can rival the brightness of an entire galaxy, and its remnants can be seen for centuries. The Crab Nebula is one such remnant. x
  • 54
    White Dwarf Supernovae—Stealing to Explode
    Supernovae come in several types, based primarily on their spectra. This lecture focuses on the important, hydrogen-deficient subclass called Type Ia, in which a white dwarf robs gas from its companion star and then becomes violently unstable. x
  • 55
    Core-Collapse Supernovae—Gravity Wins
    Type II supernovae, whose spectra exhibit hydrogen, come from massive supergiant stars whose core suddenly collapses, ejecting the rest of the star. This mechanism also applies to "stripped" stars that had previously lost their outermost layers through winds and transfer to companions. x
  • 56
    The Brightest Supernova in Nearly 400 Years
    In 1987 a Type II supernova only 170,000 light years away became visible. Earlier photos of the region showed that the exploded star was a blue supergiant, a previously unsuspected candidate for this fate. Ghostly neutrinos were detected from this supernova. x
  • 57
    The Corpses of Massive Stars
    The imploding core of a Type II supernova typically forms a bizarre, enormously compact object called a neutron star, consisting entirely of tightly packed neutrons, a teaspoon of which would weigh about a billion tons. x
  • 58
    Einstein's General Theory of Relativity
    Understanding the enormous gravitational fields of neutron stars requires Einstein's general theory of relativity, which postulates that gravity is a manifestation of the warping of space and time produced by matter and energy. x
  • 59
    Warping of Space and Time
    This lecture explores observational tests of general relativity. Astronomers exploit its effects by searching for distant objects that are gravitationally lensed, which occurs when an object's light is bent and focused by foreground masses such as galaxy clusters. x
  • 60
    Black Holes—Abandon Hope, Ye Who Enter
    If a neutron star exceeds two to three solar masses, it becomes unstable and collapses. The resulting object is called a black hole—a region of such extreme space-time curvature that nothing, not even light, can escape. x
  • 61
    The Quest for Black Holes
    Because they don't emit any light, black holes can't be seen directly. But they reveal their presence through their gravitational influence on other objects. This lecture looks at the methods astronomers use to track them down. x
  • 62
    Imagining the Journey to a Black Hole
    What's a black hole really like? Without taking the fatal journey into one, astronomers can calculate the bizarre experiences that would ensue, including dramatic distortions in visual phenomena as a traveler approached the event horizon. x
  • 63
    Wormholes—Gateways to Other Universes?
    Rotating black holes appear to connect our Universe to others or provide shortcuts—or wormholes—within our Universe. This raises the theoretical possibility of time travel, although several factors seem to rule it out. x
  • 64
    Quantum Physics and Black-Hole Evaporation
    Originally, astronomers thought that black holes were truly black, but physicist Stephen Hawking has calculated that black holes slowly evaporate through a quantum mechanical process. Very small black holes should literally explode as a burst of gamma rays! x
  • 65
    Enigmatic Gamma-Ray Bursts
    Roughly once per day, somewhere in the sky, there is a short, intense burst of gamma rays. Most of these events originate in very distant galaxies, making them among the most powerful explosions in the Universe—but they are not evaporating black holes. x
  • 66
    Birth Cries of Black Holes
    Until recently, astronomers had no smoking gun to identify the precise location and cause of gamma-ray bursts. Now they have assembled an abundance of clues pointing to two separate mechanisms: the collapse of a massive star, and the merging of two neutron stars—in each case creating a black hole. x
  • 67
    Our Home—The Milky Way Galaxy
    Starting a series of lectures on galaxies, you begin with our home galaxy, the Milky Way. The band of light by that name is simply the Galaxy seen edge-on from our place within it. You also explore the nebulae in our Galaxy, many of which are regions of stellar birth. x
  • 68
    Structure of the Milky Way Galaxy
    How do you map the structure of a galaxy when you live inside it? Astronomers have used various clues to infer the spiral structure of the Milky Way, the orbital speed of its stars, and the existence of a supermassive black hole at its center. x
  • 69
    Other Galaxies—"Island Universes"
    The discovery of other galaxies beyond the Milky Way was one of the great scientific detective stories of the early 20th century. Astronomers now know that there are hundreds of billions of galaxies, spanning billions of light years of space. x
  • 70
    The Dark Side of Matter
    Until a few decades ago, astronomers thought that galaxies were composed primarily of stars. There is now strong evidence that most of the mass of galaxies may be invisible dark matter. Clusters of galaxies are also dominated by dark matter. x
  • 71
    Cosmology—The Really Big Picture
    This lecture starts the study of the Universe as a whole—or cosmology. A key finding made by Edwin Hubble in 1929 was that the spectra of distant galaxies are redshifted more than those of nearby galaxies, suggesting that the Universe is expanding. x
  • 72
    Expansion of the Universe and the Big Bang
    The Universe can be thought of as expanding into a mathematical dimension to which we have no physical access. Even an infinite Universe can expand, becoming less dense. The expansion suggests that there was a hot, dense beginning long ago—a Big Bang. x
  • 73
    Searching for Distant Galaxies
    The finite speed of light allows observers to look back in time and see the unfolding history of the Universe. This lecture shows how astronomers search for distant galaxies to compare with better understood, nearby galaxies. x
  • 74
    The Evolution of Galaxies
    How do galaxies form and evolve over time? Is it possible to determine what nearby galaxies, or even the Milky Way, once looked like? The answers can be found by examining distant galaxies that formed when the Universe was young. x
  • 75
    Active Galaxies and Quasars
    The central regions of many galaxies go through an active, very luminous phase early in their development. The most powerful of these active galaxies, called quasars, shine like beacons across billions of light years of space. x
  • 76
    Cosmic Powerhouses of the Distant Past
    The high luminosity of quasars puzzled astronomers in the 1960s. How could these peculiar, star-like objects be so bright and yet so far away? Only a few light years across, they are in fact even more powerful than entire galaxies. x
  • 77
    Supermassive Black Holes
    Astronomers now have strong evidence that quasars and other active galactic nuclei are powered by supermassive black holes, voraciously swallowing surrounding material. Less active galaxies also appear to harbor these monsters. x
  • 78
    Feeding the Monster
    This lecture explores the disks of gas around supermassive black holes. Material escaping from the vicinity of these objects often follows a highly focused jet along the rotation axis of the disk, sometimes approaching or even appearing to surpass the speed of light. x
  • 79
    The Paradox of the Dark Night Sky
    Why is the sky dark at night? In an infinitely old and large Universe the sky should be ablaze with light at all times. There are several possible answers to this paradox, each of which has profound cosmological implications. The relative youth of the Universe is now known to be the main explanation. x
  • 80
    The Age of the Universe
    How old is the Universe? The Hubble Space Telescope was designed, in part, to answer this question. You follow the chain of reasoning that has led astronomers to conclude that the Universe began 13.7 billion years ago. x
  • 81
    When Geometry Is Destiny
    According to general relativity, the fate of the Universe is tied to its global geometry. If the Universe has positive curvature, like a sphere, it must eventually collapse in a "Big Crunch." If it is flat or has negative curvature, however, it will expand forever. x
  • 82
    The Mass Density of the Universe
    This lecture explores methods used by astronomers to determine the mass density and expansion history of the Universe. To make this measurement, a race developed between two teams of astronomers searching for Type Ia supernovae in distant galaxies. x
  • 83
    Einstein's Biggest Blunder?
    The unexpected finding that the Universe is expanding at an ever-faster rate lends support for the existence of a non-zero cosmological constant, a formerly discredited idea of Einstein's, which he once called his "biggest blunder." x
  • 84
    The Afterglow of the Big Bang
    An accidental discovery in 1965 overturned the "steady-state theory" of the Universe, an alternative to the Big Bang theory. The detection of a uniform microwave "glow" in all directions was exactly what was expected if the Universe was hot and dense long ago. x
  • 85
    Ripples in the Cosmic Background Radiation
    The cosmic microwave background radiation preserves intriguing details about the Universe around 380,000 years after the Big Bang, when the temperature had cooled enough so that neutral atoms formed, allowing photons to pass freely through space. x
  • 86
    The Stuff of the Cosmos
    The dark energy that is causing the expansion of the Universe to accelerate makes up about 75 percent of the cosmos. Ordinary matter glowing at any wavelength, optical or otherwise, accounts for less than 5 percent. The remainder is dark matter, most of which may consist of exotic subatomic particles. x
  • 87
    Dark Energy—Quantum Fluctuations?
    According to one idea, repulsive dark energy having a negative pressure might be the result of a non-perfect cancellation of quantum fluctuations in space—virtual particles created literally out of nothing, as predicted by quantum physics. x
  • 88
    Dark Energy—Quintessence?
    This lecture looks at problems with the quantum fluctuations explanation for dark energy. One alternative is called quintessence?—a class of models that postulate repulsive energy that may be associated with unified forces or fields. x
  • 89
    Grand Unification & Theories of Everything
    A major effort is underway to unify the mutually inconsistent theories of general relativity and quantum mechanics into a theory of everything. Successfully explaining dark energy might serve as an observational test for such a theory. x
  • 90
    Searching for Hidden Dimensions
    The leading contenders for a theory of everything are string theories, which postulate that fundamental particles act like tiny, vibrating strings of energy. This approach requires at least 10 dimensions, most of which are curled up on minuscule size scales. x
  • 91
    The Shape, Size, and Fate of the Universe
    Is the Universe a finite bubble in a higher-dimensional space? Or, is it infinite regardless of whether it's imbedded in extra dimensions? Will it expand forever or ultimately recollapse? If it does expand forever, how will this limitless future unfold? x
  • 92
    In the Beginning
    This lecture turns back the clock to almost the moment of creation—a fraction of a second after the Big Bang—and follows events as they sort themselves out, from what may have been packages of space-time foam winking in and out of existence, to conditions conducive for star and galaxy formation. x
  • 93
    The Inflationary Universe
    The remarkable large-scale uniformity and "flatness" of the Universe pose a problem for the standard Big Bang theory. A startling but powerful suggested explanation is that the Universe went through an initial period of exponential expansion, called inflation. x
  • 94
    The Ultimate Free Lunch?
    Why should inflation have occurred? Theorists have proposed several intriguing ideas, including that the Universe, whose total energy is quite possibly equal to zero, formed from a random quantum fluctuation that grew to gargantuan proportions. x
  • 95
    A Universe of Universes
    If a quantum fluctuation gave rise to our Universe, must ours be the only one? Are others possible, perhaps even with different rules? This lecture examines reasons for suspecting the existence of other universes, though we do not know how to test for their presence. x
  • 96
    Reflections on Life and the Cosmos
    The course ends on a philosophical note, with reflections on intelligent life in the cosmos and of our place in its grand structure. Perhaps the most astonishing thing about the Universe is that we are able to contemplate and understand it through systematic studies. x

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DVD Includes:
  • 96 lectures on 16 DVDs
  • 552-page printed course guidebook
  • Downloadable PDF of the course guidebook
  • FREE video streaming of the course from our website and mobile apps

What Does The Course Guidebook Include?

Video DVD
Course Guidebook Details:
  • 552-page course synopsis
  • Charts, tables & diagrams
  • Photos & illustrations
  • Suggested readings

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Your professor

Alex Filippenko

About Your Professor

Alex Filippenko, Ph.D.
University of California, Berkeley
Dr. Alex Filippenko is Professor of Astronomy and the Richard and Rhoda Goldman Distinguished Professor in the Physical Sciences at the University of California, Berkeley. He earned his B.A. in Physics from the University of California, Santa Barbara, and his Ph.D. in Astronomy from the California Institute of Technology. Dr. Filippenko's research accomplishments, documented in more than 500 scientific publications and 600...
Learn More About This Professor
Also By This Professor


Understanding the Universe: An Introduction to Astronomy, 2nd Edition is rated 4.8 out of 5 by 314.
Rated 5 out of 5 by from very comprehensive and challenging I am just getting into the lectures and I am most impressed by how much work and time had to have gone into the creation of this course. Nicely done!!
Date published: 2018-01-31
Rated 5 out of 5 by from Long Course--But Well Worth It Wow this is a long course--at 16 discs, 96 lectures, 48 hours, it's by far the longest course I've purchased from The Great Courses. I was diffident about buying such a long course--would I like it? Would I ever finish it? Then he started in a way I never expected. It's quite common for courses on astronomy to begin with the Ptolemaic system or ancient observatories, then move to the discovery that the earth actually orbits the sun, and on from there with a loosely historical approach to our discoveries about the universe. Instead Dr. Filippenko started with: our sky! He talked about rainbows, sunrises and sunsets. A most novel way to begin explaining modern astronomy, I thought, and I certainly would not have sought out, on my own, a lecture about rainbows and sunsets. Yet I found it quite interesting, and also presenting some phenomena I had never heard about before... Dr. Filippenko has a well-deserved reputation as a great educator and it's on display in this course. Once I started, I couldn't stop. He touched on pretty much every topic that could come to mind in an astronomy course, from rainbows to theories about multiverses. Although I had already listened to Mark Whittle's really excellent series on Cosmology, I found all of this course worthwhile. Thanks, Dr. Filippenko and thank you, The Teaching Company.
Date published: 2018-01-27
Rated 4 out of 5 by from Thrilling. Too much math for me. Needs more verbal Wonderful! Could you dumb it down a bit, with less math symbols, for those on the other side of C.P. Snow's divide?
Date published: 2018-01-21
Date published: 2018-01-01
Rated 5 out of 5 by from Best Great Course ever I have bought and borrowed many Great Courses. This one stands out. It is undoubtedly my all time favorite. It is long and pricey, but worth it.
Date published: 2017-12-13
Rated 4 out of 5 by from Good visuals Only watched two cd's so far, very good materials and presentation
Date published: 2017-12-09
Rated 5 out of 5 by from We Know Very Little While I was watching, the impeccable nerve nodes started vibrating reminding me what we know is infinitely small right from, about a simple rainbow. The Professor's immense taste is transferred to us, impulsively raising a question, can we really make it, capturing the lot?
Date published: 2017-10-31
Rated 5 out of 5 by from Astronomy 101 This course in Astronomy is outstanding!! I took Astronomy in college which was a very good course but this is even better!! More up to date with better explanations. I highly recommend this course for anyone interested in Astronomy!!!
Date published: 2017-10-20
Rated 5 out of 5 by from Wow! I have always been interested in Astronomy, so when this course went on sale, I bought it. I am so glad I did! This course provided the scope and depth on Astronomy that I was hoping for. Professor Filippenko does a great job in presenting a comprehensive survey of the subject. I highly recommend this course.
Date published: 2017-09-29
Rated 5 out of 5 by from telescopes and stars bought the DVD for the grandchildren and I started to watch it from the digital library, have not finished but the lessons I have seen are extremely enlightening. For all of us who are Drunk on Awe, the visuals are great.
Date published: 2017-09-21
Rated 5 out of 5 by from Great teacher. Very impressive presentation loaded with good information. I am glad I purchased it.
Date published: 2017-09-07
Rated 5 out of 5 by from Great course tought by great gifted professor Although I have not gone yet through the entire course, I'm rather impressed by the quality of the content and, in particular, by the presentation skills of professor Alex Filippenko. His obvious passion towards the subject of his lectures and unusual talent to explain complex concepts in plain, easy to understand language deserve the highest credit.
Date published: 2017-08-30
Rated 5 out of 5 by from Third Time I am on my third pass through the course and it will not be my last. Alex makes the materials consumable by non scientists -- adding enough of the detail that you cannot help wanting more. His enthusiasm is contagious -- as if he humbly knows the secrets of the universe and wants to share them. I think he does.
Date published: 2017-07-25
Rated 5 out of 5 by from A Great Foundation for Understanding our Universe A well prepared lecture series, presented by superb professor with a great grasp of the subject, a graphics support group able to graphically support the class sessions and and presented to the listener in an increasing technical level based on a strong background by the previous sessions. Very uplifting. Long program but well paced to deliver the picture the professor want each to get. Going to redo the Hubble telescope now being able to understand the universe we live in with all it's beauty and limitations. Suggest the Great Courses people consider a certificate of completion for those that completed the full course
Date published: 2017-07-24
Rated 5 out of 5 by from A Course About Everything If you are curious about the universe but are not a physicist, this is the perfect course for you. Covers cosmology, physics, optics, chemistry and makes it all understandable and exciting. You can understand these things. The professor is absolutely great, full of knowledge, humor, fun, and humility. Many visual aids, many simple experiments, much laughter combined with learning This is the best course I've taken anywhere and I've taken a lot!
Date published: 2017-07-20
Rated 5 out of 5 by from Content & presentation excellent! Purchased the course as an alternative to structured learning (such as university). I'm a senior citizen looking to expand his horizons (no pun intended). This is not the first course purchased, nor will it be my last. Great organization, well done!
Date published: 2017-06-09
Rated 5 out of 5 by from Understanding the Universe: An Introduction to Ast This course is 16 cd's long. I just finished my first cd and so far it is everything I had hoped for. Every topic has been explained in terms even I can understand. Complete with great visualizations to further explain the points being presented. I'm still early into this course but from what I have seen so far I'm sure the rest of it will be great as well.
Date published: 2017-05-22
Rated 5 out of 5 by from Absolutely fantastic I have completed the entire course and found it amazing. Over the 96 lectures you are taken on a journey from learning about the different colours of the sun rise all the way through to the most mind blowing concepts of quantum mechanics and parallel universes.Prof Filippenko has a fantastic infectious enthusiasm throughout and has a real gift for explaining difficult concepts in understandable ways. I was so impressed with the course I have bought his test book and will definitely be re watching the entire course soon. I had been considering buying the course for a coupe of years but the cost was fairly high. I'm now sure I've made the correct decision because now every time I walk outside day or night there are amazing things I have learnt from this course that I wold have never noticed or understood before. This course just makes you realise how much more there is in the universe than just what's happening to you today. Many thanks indeed for such a wonderful course.
Date published: 2017-04-30
Rated 5 out of 5 by from A great course! For myself, I am enjoying this course. I have only viewed five lessons so far but I have obtained great information that has helped me with my astronomy interests. This course has already increased my novice level knowledge of astronomy. It is fun to take what I have learned and apply it to my sky gazing activities. Don't feel like a novice anymore.
Date published: 2017-04-12
Rated 5 out of 5 by from Excellent Presentation The instructor obviously loves the subject and loves to teach. He has clearly spent thousands of hours learning the subject matter and hundreds of hours preparing and obtaining visuals, teaching aids, demonstrations, etc. to make the subject matter clearer, more interesting and easier to understand.
Date published: 2017-04-08
Rated 5 out of 5 by from Immensely compelling I am experienced in astrophysics and this course still taught me a lot. I was pleasantly surprised to find lectures delving deep into each planet, the types of stars, the differences between type 1a and 1b supernovae, and just about every other topic there is to cover in astronomy. If you are an astronomy or space geek, I very highly recommend this course. There are a lot of lectures, but I would go back and listen to them all again. One aspect of astronomy that people tend to overlook is that of earthly phenomena such as rainbows, aurorae, the sunrise, and eclipses. Mr. Filippenko covers it all with substantial explicit detail. I am not the biggest fan of Alex Filippenko, he’s terribly corny, but his fervor and passion for everything astronomy is very infectious. His knowledge base is quite impressive. He is an experienced astronomer, scientist, observer, and professor. He approaches every topic with enthusiasm and brings his own extensive knowledge and practical experience into the subject. He truly is a magnificent teacher.
Date published: 2017-03-08
Rated 5 out of 5 by from Excellent I bought this for my son's birthday. He had seen it in the catalog and wanted it. He is binge watching it as I write this. It's content is extensive and presented well. Delighted with this purchase.
Date published: 2017-02-02
Rated 3 out of 5 by from Amateurish, Dummed Down Presentation I always enjoyed hearing Prof Filippenko's comments on TV shows so I purchased this course. I am sad to say that I was really disappointed. First, Prof Filippenko stands behind a stand up desk with his laptop and never moves away from it. He has a few people sitting in front of him to simulate a class. The problem is he frequently talks to them instead of to the viewer this video. I found this annoying. He needs to look into the camera so that he is talking to the viewers of the video...get rid of the "class". Also he is constantly looking at his laptop and talking to his laptop. Other professors in these courses have large screens behind them where professional graphics and visuals appear, coinsiding with what he is saying. Graphics and visuals in this course are very amateurish. This presentation may be OK for a classroom but not for a format like this. Content of the course is very simplistic...not college level at all...more like for high school students. He spends way too much time on some areas such as rainbows...."all right already, we got it, move on". Some sections of this course seem to just drag on and on. Prof Filippenko seems very uncomfortable with his presentation, nervous, and not the brilliant scientist I know he is. If he does more of these courses I encourage him to hire a presentation professional so he can present a quality, well-written, well-presented, visually professional course. For a top quality, professionally produced course check out the course on Organic Chemistry with Professor Davis.
Date published: 2017-01-21
Rated 5 out of 5 by from Astronomy Tour of the Universe This Great Courrse is filled with information and provided an overview of Astronomy for the non-astronomy casual observer of the sky above. Professor Filippenko adds an occasional personal touch to his lecturues and it's easy to see why he gets high marks from students at Cal. Thsi is the only Astronomy course I've ever taken and it's outstanding.
Date published: 2016-12-29
Rated 5 out of 5 by from Quite an Undertaking I have listened to a lot of Great Courses, but this is by far the longest that I've undertaken so far. First, let me say that I was definitely not a science major, but I've always had some interest in astronomy. Overall, I enjoyed this course very much. The professor is incredibly enthusiastic and put a lot of effort into making hard scientific terms understandable. That being said, some of the material still went over my head. Viewers should either be ready to tackle some reasonably difficult scientific and mathematical concepts or accept that some portions of the course just have to be glossed over. Still, most of the course was very understandable, and what I learned was very interesting. Of course, the biggest deficiency with the course is that it is nearly ten years old, and a lot has happened in the field of astronomy in the last decade. For instance, the professor speculates several times on the scientific knowledge to be gained when the James Webb Space Telescope launches in 2013…but the estimated launch date is now late 2018. The course is due for an update, but it is still more than worthwhile. This course took dedication to get through it all, but I'm glad that I did.
Date published: 2016-12-13
Rated 4 out of 5 by from I have only watched 6 classes. I have only watched six classes. But very informative.
Date published: 2016-12-10
Rated 5 out of 5 by from What a Delight! My wife and I are glued to this course. The professor's enthusiasm for the topic is contagious. Each lecture has new surprises and brings clarity to many topics. This is a great course for the whole family.
Date published: 2016-11-25
Rated 5 out of 5 by from I Never Thought I Could Learn Astronomy I'm older with little mathematical backround. A child of the space program era, I wanted to understand but was afraid because of its technical language. This course dispelled these myths. The teacher paces his explanations which must be hard for one so enthusiastic about his topic. Hoping my grandkids will also watch it, Among the five girls and one boy maybe a future astronomer.
Date published: 2016-11-17
Rated 5 out of 5 by from Favourite course ever Alex Filippenko is second to none in his crystal clear explanations and the unbounded enthusiasm he brings to his subject. His depth of knowledge and use of simple and concrete visual aids help enormously in understanding the subject matter. This is my favorite course ever..
Date published: 2016-10-31
Rated 5 out of 5 by from Understanding the Universe: 2nd Edition I'm about a third of the way through this course and so far have enjoyed it immensely. Very impressive. 100% satisfied.
Date published: 2016-10-23
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