Welcome to the first episode of Crash Course Astronomy. Your host for this intergalactic adventure is the Bad Astronomer himself, Phil Plait. We begin with answering a question: "What is astronomy?" Air Date : 15th-Jan-2015  Read More

Phil invites you to head outside and take a look at all the incredible things you can see with your naked eye. Air Date : 22nd-Jan-2015  Read More

This week we build on our naked eye observations from last week and take a look at the cyclical phenomena that we can see at work in the universe. Air Date : 29th-Jan-2015  Read More

In this episode of Crash Course Astronomy, Phil takes you through the cause and name of the Moon's phases. Air Date : 5th-Feb-2015  Read More

The big question in the comments last week was, "BUT WHAT ABOUT ECLIPSES?" Today, Phil breaks 'em down for you. Air Date : 13th-Feb-2015  Read More

Today Phil explains how telescopes work and offers up some astronomical shopping advice. Air Date : 19th-Feb-2015  Read More

In today's episode, Phil looks at how gravity plays out across the universe. Air Date : 26th-Feb-2015  Read More

Today Phil explores the world of tides! What is the relationship between tides and gravity? How do planets and their moons become tidally locked? What would happen if you were 300km tall? Important questions. Air Date : 5th-Mar-2015  Read More

In today's Crash Course Astronomy, Phil takes a look at the explosive history of our cosmic backyard. We explore how we went from a giant ball of gas to the system of planets and other celestial objects we have today. Air Date : 12th-Mar-2015  Read More

Phil takes us for a closer (eye safe!) look at the two-octillion ton star that rules our solar system. We look at the sun's core, plasma, magnetic fields, sunspots, solar flares, coronal mass ejections, and what all of that means for our planet. Air Date : 19th-Mar-2015  Read More

Phil starts the planet-by-planet tour of the solar system right here at home, Earth. Air Date : 2nd-Apr-2015  Read More

Join Phil for a tour of our capital-M Moon, from surface features, inside to the core, and back in time to theories about its formation. Air Date : 9th-Apr-2015  Read More

Mercury is the closest planet to the sun. It has no atmosphere and is, as such, covered in craters. It's also incredibly hot but, surprisingly, has water ice hiding beneath its surface. Air Date : 16th-Apr-2015  Read More

Venus is a gorgeous naked-eye planet, hanging like a diamond in the twilight -- but it’s beauty is best looked at from afar. Even though Mercury is closer to the sun, Venus is the hottest planet in the solar system, due to a runaway greenhouse effect, and has the most volcanic activity in the solar system. Its north and south poles were flipped, causing it to rotate backwards and making for very strange days on this beautiful but inhospitable world. Air Date : 23rd-Apr-2015  Read More

The fourth planet from the sun and the outermost of the terrestrial planets, Mars has long been a popular spot for missions and imagination. Phil walks you through the planet's topography, core, and features. We'll take a look back to Mars's past and makes predictions for its future, including the possibilities for human life. Air Date : 30th-Apr-2015  Read More

Jupiter is the biggest planet in our solar system. The gas giant is NOT a failed star, but a really successful planet! It has a dynamic atmosphere with belts and zones, as well as an enormous red spot that’s actually a persistent hurricane. Jupiter is still warm from its formation, and has an interior that’s mostly metallic hydrogen, and it may not even have a core. Air Date : 8th-May-2015  Read More

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 4 huge ones that we want to explore in greater detail. Ganymede is the largest - larger, in fact, than any other moon in the solar system and the planet Mercury! Callisto, orbiting the farthest out, is smaller but quite similar to Ganymede in many ways. Io, meanwhile, is most noteworthy for its tremendous volcanic activity. There’s also water on Ganymede and Europa! Air Date : 14th-May-2015  Read More

Saturn is the crown jewel of the solar system, beautiful and fascinating. It is a gas giant, and has a broad set of rings made of ice particles. Moons create gaps in the rings via their gravity. Saturn has dozens of moons, including Titan, which is as big as Mercury and has a thick atmosphere and lakes of methane; and Enceladus which has an undersurface ocean and eruptions of water geysers. While we are still uncertain, it is entirely possible that either or both moons may support life. Air Date : 21st-May-2015  Read More

Today we’re rounding out our planetary tour with 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 rotation and relatively dull weather, while Neptune has clouds and storms whipped by tremendous winds. Both have rings and moons, with Neptune’s Triton probably being a captured iceball that has active geology. Air Date : 28th-May-2015  Read More

Now that we’ve finished our tour of the planets, we’re headed back to the asteroid belt. Asteroids are chunks of rock, metal, or both that were once part of smallish planets but were destroyed after collisions. Most orbit the Sun between Mars and Jupiter, but some get near the Earth. The biggest, Ceres is far smaller than the Moon but still big enough to be round and have undergone differentiation. Air Date : 4th-Jun-2015  Read More

Today on Crash Course Astronomy, Phil explains comets. 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. Air Date : 18th-Jun-2015  Read More

Now that we’re done with the planets, asteroid belt, and comets, we’re heading to the outskirts of the solar system. 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 shape aligned with the plane of the solar system; the scattered disk is more eccentric and is the source of short period comets; and the Oort Cloud which surrounds the solar system out to great distances is the source of long-period comets. These bodies all probably formed closer into the Sun, and got flung out to the solar system’s suburbs by gravitational interactions with the outer planets. Air Date : 25th-Jun-2015  Read More

Today Phil helps keep you from ticking off an astronomer in your life by making sure you know the difference between a meteor, meteorite, and meteoroid. 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 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. Air Date : 2nd-Jul-2015  Read More

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. Air Date : 9th-Jul-2015  Read More

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 find the size of the Earth, and from that the distance to and the sizes of the Moon and Sun. Once the Earth/Sun distance was found, parallax was used to find the distance to nearby stars, and that was bootstrapped using brightness to determine the distances to much farther stars. Air Date : 16th-Jul-2015  Read More

Today Phil’s explaining the stars and how they can be categorized using their spectra. Together with their distance, this provides a wealth of information about them including their luminosity, size, and temperature. The HR diagram plots stars’ luminosity versus temperature, and most stars fall along the main sequence, where they live most of their lives. Air Date : 23rd-Jul-2015  Read More

Today Phil explains that YES, there are other planets out there and astonomers have a lot of methods for detecting them. Nearly 2000 have been found so far. The most successful method is using transits, where a planet physically passes in front of its parent star, producing a measurable dip in the star’s light. Another is to measuring the Doppler shift in a star’s light due to reflexive motion as the planet orbits. Exoplanets appear to orbit nearly every kind of star, and we’ve even found planets that are the same size as Earth. We think there may be many billions of Earth-like planets in our galaxy. Air Date : 30th-Jul-2015  Read More

While Jupiter is nowhere near massive enough to initiate fusion in its core, there are even more massive objects out there that fall just short of that achievement as well called brown dwarfs. Brown dwarfs, have a mass that places them between giant planets and small stars. They were only recently discovered in the 1990’s, but thousands are now known. More massive ones can fuse deuterium, and even lithium, but not hydrogen, distinguishing them from “normal” stars. Sort of. Air Date : 13th-Aug-2015  Read More

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 (and also some oxygen and neon). When this happens they expand, get brighter, and cool off, becoming red giants. They lose most of their mass, exposing their cores, and then cool off over many billions of years. Air Date : 20th-Aug-2015  Read More

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. They only last a few millennia. The Sun probably won’t form one, but higher mass stars do. Air Date : 27th-Aug-2015  Read More

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 shock wave, together with a huge swarm of neutrinos, blast through the star’s outer layers, causing it to explode. The resulting supernova creates even more heavy elements, scattering them through space. Also, happily, we’re in no danger from a nearby supernova. Air Date : 10th-Sep-2015  Read More