Crash Course Astronomy


  • Comets | Crash Course Astronomy

    Comets are chunks of ice and rock that orbit the Sun. When they get near the Sun, the ice turns into gas, forming the long tail, and also releases dust that forms a different tail. We've visited comets up close and found them to be lumpy, with vents in the surface that release the gas as ice sublimates. Eons ago, comets (and asteroids) may have brought a lot of water to Earth-as well as the ingredients for life.

    Grades: 9-12
  • The Oort Cloud | Crash Course Astronomy

    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 Scattered Disk is an eccentric region, and the source of short-period comets. The Oort Cloud, which surrounds the solar system out to great distances, is the source of long-period comets.

    Grades: 9-12
  • Meteors | Crash Course Astronomy

    Meteors are small bits of interplanetary debris broken off from asteroids or comets. When the Earth plows through the stream emitted by a comet, we get a meteor shower. Meteors burn up about 100 km above the Earth, but some survive to hit the ground. Most of these meteorites that reach Earth are rocky, some are metallic, and a few are a mix of the two. Very big meteorites can be a very big problem, but there are plans in the works to prevent us from going the way of the dinosaurs.

    Grades: 9-12
  • Light | Crash Course Astronomy

    In order to understand how we study the universe, we need to talk a little bit about light. Light is a form of energy. Its wavelength tells us its energy and color. Spectroscopy allows us to analyze those colors and determine an object's temperature, density, spin, motion, and chemical composition.

    Grades: 9-12
  • Distances | Crash Course Astronomy

    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 that, the distance to and sizes of the Moon and Sun. Once the distance between the Earth and Sun was found, parallax was used to determine the distance to nearby stars.

    Grades: 9-12
  • Stars | Crash Course Astronomy

    Phil explains the stars and how they can be categorized using their spectra. Together with distance, a star's spectra provides a wealth of information, including their luminosity, size, and temperature. We also learn about the HR diagram, which plots a star's luminosity versus its temperature.

    Grades: 9-12
  • Exoplanets | Crash Course Astronomy

    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 front of its parent star, producing a measurable dip in the star's light. Exoplanets appear to orbit nearly every kind of star, and we've even found planets that are the same size as Earth. Astronomers think there may be many billions of Earth-like planets in our galaxy.

    Grades: 9-12
  • Brown Dwarfs | Crash Course Astronomy

    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 between giant planets and small stars. They were only recently discovered in the 1990s, but thousands are now known. More massive ones can fuse deuterium, and even lithium, but not hydrogen, distinguishing them from normal stars.

    Grades: 9-12
  • Low Mass Stars | Crash Course Astronomy

    Today we are talking about the life—and death—of stars. Low mass stars live a long time, fusing all their hydrogen into helium over a trillion years. More massive stars like the Sun live shorter lives. They fuse hydrogen into helium, and eventually helium into carbon. When this happens they expand, get brighter, and cool off, becoming red giants.

    Grades: 9-12
  • White Dwarfs & Planetary Nebulae | Crash Course Astronomy

    Today Phil follows up last week's look at the death of low mass stars with what comes next: a white dwarf. White dwarfs are incredibly hot and dense objects roughly the size of Earth. They also can form planetary nebulae: huge, intricately detailed objects created when the wind blown from the dying stars is lit up by the central white dwarf.

    Grades: 9-12
  • High Mass Stars | Crash Course Astronomy

    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 more heavy elements, scattering them through space.

    Grades: 9-12
  • Neutron Stars | Crash Course Astronomy

    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 magnetic fields are called magnetars, and are capable of colossal bursts of energy that can be detected over vast distances.

    Grades: 9-12
  • Black Holes | Crash Course Astronomy

    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 light.

    Grades: 9-12
  • Binary and Multiple Stars | Crash Course Astronomy

    Double stars are stars that appear to be near each other in the sky, but if they're gravitationally bound together we call them binary stars. Many stars are actually part of binary or multiple systems. In some close binaries matter can flow from one star to the other, changing the way it ages.

    Grades: 9-12
  • Star Clusters | Crash Course Astronomy

    Last week we covered multiple star systems, but what if we added thousands or even millions of stars to the mix? A star cluster.

    Grades: 9-12
  • Nebulae | Crash Course Astronomy

    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 years across.

    Grades: 9-12
  • The Milky Way | Crash Course Astronomy

    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.

    Grades: 9-12
  • Galaxies, Part 1 | Crash Course Astronomy

    Galaxies contain gas, dust, and billions of stars or more. They come in four main shapes: elliptical, spiral, peculiar, and irregular. Galaxies can collide, and grow in size by eating each other.

    Grades: 9-12
  • Galaxies, Part 2 | Crash Course Astronomy

    Active galaxies pour out lots of energy, due to their central supermassive black holes gobbling down matter. Galaxies tend not to be loners, but instead exist in smaller groups and larger clusters. Our Milky Way is part of the Local Group, and will one day collide with the Andromeda galaxy.

    Grades: 9-12
  • Gamma-Ray Bursts | Crash Course Astronomy

    Gamma-ray bursts are not only incredible to study, but their discovery has an epic story all its own. Today Phil takes you through some Cold War history and then dives into what we know.

    Grades: 9-12

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