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Introduction to Astrophysics

A Princeton astrophysicist teaches you how to solve the problems that sparked a new understanding of the universe.
Introduction to Astrophysics is rated 4.6 out of 5 by 148.
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Rated 5 out of 5 by from Excellent Familiarity with mathematical concepts (algebra, trig. & calculus) and basic physics helps understanding, but avoiding getting bogged down in that and concentrating on the concepts and conclusions still provides a great learning experience. Great lecturer.
Date published: 2022-11-26
Rated 5 out of 5 by from Beyond hand-waving and nice pictures Brilliantly presented with an emphasis on understanding the key concepts. While so many astrophysics documentaries skip even the most basic math and resort to unsatisfying hand-waving and nice pictures, this one leaves you with a deeper understanding. It avoids calculus in favor of easy-to-follow unit analysis. Bravo.
Date published: 2022-10-26
Rated 5 out of 5 by from So interesting and well presented. I really enjoyed the course. I learned so many facts I didn't know. Professor Winn's knowledge and presentation of this fascinating field is outstanding. I highly recommend it.
Date published: 2022-10-05
Rated 5 out of 5 by from Well Planned Course I found this course excellent, covering topics I have wondered about for years. Because I had a background in math and physics it was easier to follow, but that background was 50 years ago. The presentation was well gauged to gradually carry through the difficult parts and the very complicated math was eased by appropriate assumptions and simplifications, as well as 'scaling' to common units (such as those related two our sun).
Date published: 2022-08-06
Rated 5 out of 5 by from Full of Information – Challenging Regarding my rating for this course, I was undecided. It was either 5 stars or 3 – let me explain. Why 3 stars – well, the course was not a walk in the park – it was complex, abstract, and very challenging. The contents included difficult subjects such as quantum theory, relativity, and a lot of high-level math. Professor Winn included discussions on mind-boggling matters such as the Pauli exclusion principle, the Heisenberg uncertainty principle, degeneracy pressure, the Chandrasekhar limit – these are just a few examples. Why 5 stars – well, the course is full of information such as measuring orbits, calculating distances between galaxies, determining the chemistry of the universe, imagining how the universe was created. It seems miraculous how science has reached these accomplishments. It's amazing how much we do understand about the universe and how much we do not. I have to believe that much of Dr. Winn's lectures is not totally correct due to assumptions and guesses, but the lectures show how much mankind has learned. I finally settled on 5 stars because there is so much information and because of the professor's outstanding presentation. He talks methodically and is easy to follow. I especially appreciate his style of speaking to his audience instead of just reading. The course is fast paced and covers a lot of ground. Personally, I think he covered too much ground. There is enough content for several courses. As we got towards the end of the lectures, I could not understand many of the issues such as dark matter – it was just over my head. Also, the Guide Book was not of much help because it contains a lot of math and complexity. As I was listening to Dr. Winn's lectures, I could not help thinking about Stephen Hawkings. He wrote some books with the intention of making the universe easier to understand. However, his books made the universe even more difficult to understand. This happened in some parts of this course. In conclusion, I enjoyed the course and how well Dr Winn presented. I recommend it, but be prepared for challenges.
Date published: 2022-08-05
Rated 5 out of 5 by from What a course should be. First, the professor is excellent. This is what physics course should be. A great presentation of physics and math. This is one of my favorite courses. I am 83 years old and I really appreciate Great Courses providing courses for people like myself who do not live near a good university. I enjoy learning now more than ever. The book that comes with the course is also very well written. Thanks professor Winn for a job very well done.
Date published: 2022-04-28
Rated 5 out of 5 by from Exceptionally well done and worthwhile. Hard to stop once I got started. Really interesting and well explained.
Date published: 2022-04-10
Rated 5 out of 5 by from Good explanations. I enjoyed taking a physical science course that is based on calculus. Dr Winn does a good job off explaining the concepts with a nice sense of enthusiasm. One can glean a lot even without proficiency in math. A fascinating subject.
Date published: 2022-03-20
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Taught by Professor Joshua Winn of Princeton University, this course takes you step by step through the major calculations of astrophysics, including Newton's law of gravity, a black hole's event horizon, the ignition temperature of a star, and many more. Knowledge of first-year college physics and math is assumed, but Dr. Winn-an award-winning teacher-makes the course rewarding for anyone curious about the universe.


Joshua N. Winn

There are so many reasons to study exoplanets, including exploration, the search for life, the rich physics problem of planet formation, and the technological challenge.


Princeton University
Dr. Joshua N. Winn is the Professor of Astrophysical Sciences at Princeton University. After earning his Ph.D. in Physics from MIT, he held fellowships from the National Science Foundation and NASA at the Harvard-Smithsonian Center for Astrophysics. Dr. Winn's research goals are to explore the properties of planets around other stars, understand how planets form and evolve, and make progress on the age-old question of whether there are other planets capable of supporting life. He was a member of the science team of NASA's Kepler mission and is the Deputy Science Director of a future NASA mission called the Transiting Exoplanet Survey Satellite. He has authored or coauthored more than 100 scientific articles on the subject of exoplanetary science. At MIT, Dr. Winn teaches physics and astronomy and has won several awards for his dedication to his students, including the Buechner Faculty Teaching Prize in 2008 and the School of Science Prize for Excellence in Graduate Teaching in 2013. His talent for communicating science to the general public was honed during graduate school, when he wrote for the science section of The Economist.

By This Professor

The Search for Exoplanets: What Astronomers Know
Introduction to Astrophysics
Introduction to Astrophysics


Zooming Out to Distant Galaxies

01: Zooming Out to Distant Galaxies

Begin by defining the difference between astrophysics and astronomy. Then study the vast range of scales in astrophysics—from nanometers to gigaparsecs, from individual photons to the radiation of trillions of suns. Get the big picture in a breathtaking series of exponential jumps—zooming from Earth, past the planets, stars, galaxies, and finally taking in countless clusters of galaxies.

33 min
Zooming In to Fundamental Particles

02: Zooming In to Fundamental Particles

After touring the universe on a macro scale in the previous lecture, now zoom in on the microcosmos—advancing by powers of ten into the realm of molecules, atoms, and nuclei. Learn why elementary particles are just as central to astrophysics as stars and galaxies. Then review the four fundamental forces of nature and perform a calculation that explains why atoms have to be the size they are.

32 min
Making Maps of the Cosmos

03: Making Maps of the Cosmos

Discover how astrophysicists map the universe. Focus on the tricky problem of calculating distances, seeing how a collection of overlapping techniques provide a “cosmic distance ladder” that works from nearby planets (by means of radar) to stars and galaxies (using parallax and Cepheid variable stars) to far distant galaxies (by observing a type of supernova with a standard intrinsic brightness).

31 min
The Physics Demonstration in the Sky

04: The Physics Demonstration in the Sky

In the first of two lectures on motion in the heavens, investigate the connection between Isaac Newton’s laws of motion and the earlier laws of planetary motion discovered empirically by Johannes Kepler. Find that Kepler’s third law is the ideal method for measuring the mass of practically any phenomenon in astrophysics. Also, study the mathematics behind Kepler’s second law.

32 min
Newton’s Hardest Problem

05: Newton’s Hardest Problem

Continue your exploration of motion by discovering the law of gravity just as Newton might have—by analyzing Kepler’s laws with the aid of calculus (which Newton invented for the purpose). Look at a graphical method for understanding orbits, and consider the conservation laws of angular momentum and energy in light of Emmy Noether’s theory that links conservation laws and symmetry.

35 min
Tidal Forces

06: Tidal Forces

Why are the rings around Saturn and the much fainter rings around Jupiter, Uranus, and Neptune at roughly the same relative distances from the planet? Why are large moons spherical? And why are large moons only found in wide orbits (i.e., not close to the planets they orbit)? These problems lead to an analysis of tidal forces and the Roche limit. Close by calculating the density of the Sun based on Earth’s ocean tides.

32 min
Black Holes

07: Black Holes

Use your analytical skill and knowledge of gravity to probe the strange properties of black holes. Learn to calculate the Schwarzschild radius (also known as the event horizon), which is the boundary beyond which no light can escape. Determine the size of the giant black hole at the center of our galaxy and learn about an effort to image its event horizon with a network of radio telescopes.

32 min
Photons and Particles

08: Photons and Particles

Investigate our prime source of information about the universe: electromagnetic waves, which consist of photons from gamma ray to radio wavelengths. Discover that a dense collection of photons is comparable to a gas obeying the ideal gas law. This law, together with the Stefan-Boltzmann law, Wien’s law, and Kepler’s third law, help you make sense of the cosmos as the course proceeds.

34 min
Comparative Planetology

09: Comparative Planetology

Survey representative planets in our solar system with an astrophysicist’s eyes, asking what makes Mercury, Venus, Earth, and Jupiter so different. Why doesn’t Mercury have an atmosphere? Why is Venus so much hotter than Earth? Why is Jupiter so huge? Analyze these and other riddles with the help of physical principles such as the Stefan-Boltzmann law.

32 min
Optical Telescopes

10: Optical Telescopes

Consider the problem of gleaning information from the severely limited number of optical photons originating from astronomical sources. Our eyes can only do it so well, and telescopes have several major advantages: increased light-gathering power, greater sensitivity of telescopic cameras and sensors such as charge-coupled devices (CCDs), and enhanced angular and spectral resolution.

32 min
Radio and X-Ray Telescopes

11: Radio and X-Ray Telescopes

Non-visible wavelengths compose by far the largest part of the electromagnetic spectrum. Even so, many astronomers assumed there was nothing to see in these bands. The invention of radio and X-ray telescopes proved them spectacularly wrong. Examine the challenges of detecting and focusing radio and X-ray light, and the dazzling astronomical phenomena that radiate in these wavelengths.

33 min
The Message in a Spectrum

12: The Message in a Spectrum

Starting with the spectrum of sunlight, notice that thin dark lines are present at certain wavelengths. These absorption lines reveal the composition and temperature of the Sun’s outer atmosphere, and similar lines characterize other stars. More diffuse phenomena such as nebulae produce bright emission lines against a dark spectrum. Probe the quantum and thermodynamic events implied by these clues.

32 min
The Properties of Stars

13: The Properties of Stars

Take stock of the wide range of stellar luminosities, temperatures, masses, and radii using spectra and other data. In the process, construct the celebrated Hertzsprung–Russell diagram, with its main sequence of stars in the prime of life, including the Sun. Note that two out of three stars have companions. Investigate the orbital dynamics of these binary systems.

34 min
Planets around Other Stars

14: Planets around Other Stars

Embark on Professor Winn’s specialty: extrasolar planets, also known as exoplanets. Calculate the extreme difficulty of observing an Earth-like planet orbiting a Sun-like star in our stellar neighborhood. Then look at the clever techniques that can now overcome this obstacle. Review the surprising characteristics of many exoplanets and focus on five that are especially noteworthy.

33 min
Why Stars Shine

15: Why Stars Shine

Get a crash course in nuclear physics as you explore what makes stars shine. Zero in on the Sun, working out the mass it has consumed through nuclear fusion during its 4.5-billion-year history. While it’s natural to picture the Sun as a giant furnace of nuclear bombs going off non-stop, calculations show it’s more like a collection of toasters; the Sun is luminous simply because it’s so big.

34 min
Simple Stellar Models

16: Simple Stellar Models

Learn how stars work by delving into stellar structure, using the Sun as a model. Relying on several physical principles and sticking to order-of-magnitude calculations, determine the pressure and temperature at the center of the Sun, and the time it takes for energy generated in the interior to reach the surface, which amounts to thousands of years. Apply your conclusions to other stars.

34 min
White Dwarfs

17: White Dwarfs

Discover the fate of solar mass stars after they exhaust their nuclear fuel. The galaxies are teeming with these dim “white dwarfs” that pack the mass of the Sun into a sphere roughly the size of Earth. Venture into quantum theory to understand what keeps these exotic stars from collapsing into black holes, and learn about the Chandrasekhar limit, which determines a white dwarf’s maximum mass.

34 min
When Stars Grow Old

18: When Stars Grow Old

Trace stellar evolution from two points of view. First, dive into a protostar and witness events unfold as the star begins to contract and fuse hydrogen. Exhausting that, it fuses heavier elements and eventually collapses into a white dwarf—or something even denser. Next, view this story from the outside, seeing how stellar evolution looks to observers studying stars with telescopes.

33 min
Supernovas and Neutron Stars

19: Supernovas and Neutron Stars

Look inside a star that weighs several solar masses to chart its demise after fusing all possible nuclear fuel. Such stars end in a gigantic explosion called a supernova, blowing off outer material and producing a super-compact neutron star, a billion times denser than a white dwarf. Study the rapid spin of neutron stars and the energy they send beaming across the cosmos.

33 min
Gravitational Waves

20: Gravitational Waves

Investigate the physics of gravitational waves, a phenomenon predicted by Einstein and long thought to be undetectable. It took one of the most violent events in the universe—colliding black holes—to generate gravitational waves that could be picked up by an experiment called LIGO on Earth, a billion light years away. This remarkable achievement won LIGO scientists the 2017 Nobel Prize in Physics.

32 min
The Milky Way and Other Galaxies

21: The Milky Way and Other Galaxies

Take in our entire galaxy, called the Milky Way. Locate Earth’s position; then survey other galaxies, classifying their structure. Use the virial theorem to analyze a typical galaxy, which can be thought of as a “collisionless gas” of stars. Note that galaxies themselves often collide with each other, as the nearby Andromeda Galaxy is destined to do with the Milky Way billions of years from now.

32 min
Dark Matter

22: Dark Matter

Begin with active galaxies that have supermassive black holes gobbling up nearby stars. Then consider clusters of galaxies and the clues they give for missing mass—dubbed “dark matter.” Chart the distribution of dark matter around galaxies and speculate what it might be. Close with the Big Bang, deduced from evidence that most galaxies are speeding away from us; the farther away, the faster.

31 min
The First Atoms and the First Nuclei

23: The First Atoms and the First Nuclei

The Big Bang theory is one pillar of modern cosmology. Another is the cosmic microwave background radiation, which is the faint “echo” of the Big Bang, permeating all of space and discovered in 1965. The third pillar is the cosmic abundances of the lightest elements, which tell the story of the earliest moment of nucleosynthesis taking place in the first few minutes of the Big Bang.

34 min
The History of the Universe

24: The History of the Universe

In this last lecture, follow the trail of the greatest unsolved problem in astrophysics. Along the way, get a grip on the past, present, and future of the universe. Discovered in the 1990s, the problem is “dark energy,” which is causing the expansion of the universe to accelerate. Trace this mysterious force to the lambda term in the celebrated Friedmann equation, proposed in the 1920s.

37 min