Out past Neptune are vast reservoirs of icy bodies that can become comets if they get poked into the inner solar system. The Kuiper Belt is a donut-shaped region beyond the planets that is aligned with the plane of the solar system. The...

John Green teaches you about the presidency of Andrew Jackson. Jackson's election was more democratic than any previous presidential election. More people were able to vote, and they picked a doozie. Jackson was a well-known war hero,...

Massive stars fuse heavier elements in their cores than lower mass stars. This leads to the creation of heavier elements up to iron. Iron robs critical energy from the core, causing it to collapse. The resulting supernova creates even...

Before moving on from Jupiter to Saturn, we're going to linger for a moment on Jupiter's moons. There are 67 known moons, and four huge ones that we want to explore in greater detail. Ganymede is the largest - larger, in fact, than any...

John Green teaches you about the War of 1812. The War of 1812 was fought between the United States and its former colonial overlord England. John will take you through the causes of the war, tell you a little bit about the fighting...

In which John Green teaches you about the United States in the 1920s. They were known as the roaring 20s, but not because there were lions running around everywhere. In the 1920s, America's economy was booming, and all kinds of social...

We complete our planetary tour with a review of the ice giants Uranus and Neptune. Both have small rocky cores, thick mantles of ammonia, water, and methane, and atmospheres that make them look greenish and blue. Uranus has a truly weird...

There are other planets out there, and astronomers have a lot of methods for detecting them. Nearly 2000 planets have been found so far. The most successful method for finding them is using transits, where a planet physically passes in...

Host Phil Plait explains how telescopes work and offers up some astronomical shopping advice. In this episode, we learn how telescopes do two things: collect light, and increase our ability to resolve details. Learn the difference...

Today on Crash Course Astronomy, Phil dives into some very dark matters. The stuff we can actually observe in the universe isn't all there is. Galaxies and other large structures in the universe are created and shifted by a force we...

Stellar mass black holes form when a very massive star dies, and its core collapses. Black holes come in different sizes, but for all of them, the escape velocity is greater than the speed of light, so nothing can escape, not matter or...

Learn why the moon has phases and what those phases are. Because the moon is a sphere and orbiting the earth every 29.5 days, the way we see it in the night sky changes with time. Learn what the phases of the moon are: why they occur,...

In which John Green teaches you about recent history. John covers the end of George W. Bush's administration and the presidency of Barack Obama (so far). John will teach you about Obama's election, some of his policies like the...

While Jupiter is nowhere near massive enough to initiate fusion in its core, there are even more massive objects out there that fall short of that achievement, and they are called brown dwarfs. Brown dwarfs have a mass that places them...

In which John Green teaches you about the New Deal, which was President Franklin D. Roosevelt's plan to pull the United States out of the Great Depression of the 1930's. John will teach you about some of the most effective and some of...

In which John Green teaches you about the Cold War, which was the decades long conflict between the USA and the USSR. The Cold War was called cold because of the lack of actual fighting, but this is inaccurate. There was plenty of...

Today we're talking about our galactic neighborhood: The Milky Way. It's a disk galaxy, a collection of dust, gas, and hundreds of billions of stars, with the Sun located about halfway out from the center. [10:59]

In the aftermath of an 8-20 solar mass star's demise we find a weird little object known as a neutron star. Neutrons stars are incredibly dense, spin rapidly, and have very strong magnetic fields. Neutrons stars with the strongest...

How do astronomers make sense out of the vastness of space? How do they study things so far away? Today Phil talks about distances, going back to early astronomy. Ancient Greeks were able to determine the the size of the Earth, and from...

As we approach the end of Crash Course Astronomy, it's time now to acknowledge that our Universe's days are numbered. [15:00]

Astronomers study a lot of gorgeous things, but nebulae might be the most breathtakingly beautiful of them all. Nebulae are clouds of gas and dust in space. Some nebulae are small and dense, others can be dozens or hundreds of light...

Take a tour of the moon, the closest astronomical object to Earth. Learn theories of the moon's formation, understand its surface features and how they formed, like the highlands and maria, and the moon's internal structures. [9:47]

In this episode, Phil breaks down what happens during a solar and lunar eclipse and provides tips for safely viewing a solar eclipse. Learn how the Ancient Greeks calculated a close estimation of the earth and moon's actual size two...

Learn all about planet Earth, from the composition of its internal structure and core, to its shifting continental plates, and placement in the solar system. We take a tour of Earth's inner and outer core, the origins of the planet's...