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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.
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Tyler Childers (Skylion)'s profile photoSebastian Fernandez Alberdi's profile photoOliver Isenrich's profile photoBobbie Knopick's profile photo
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+Alejandro Mery
Maybe they are correcting the mistakes in the animation? :)
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Now that we've discussed blood, we're beginning our look at how it gets around your body. Today Hank explains your blood vessels and their basic three-layer structure of your blood vessels. We're also going over how those structures differ slightly in different types of vessels. We will also follow the flow of blood from your heart to capillaries in your right thumb, and all the way back to your heart again.
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Mazzawak's profile photoAlexander K.'s profile photoBobbie Knopick's profile photoOliver Isenrich's profile photo
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And doesn't the Chepalic go to the deep dorsal veins?
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Today we're talking the heart and heart throbs -- both literal and those of the televised variety. Hank explains how your heart’s pacemaker cells use leaky membranes to generate their own action potentials, and how the resulting electricity travels through the cardiac conduction pathway from SA Node to Purkinje fibers, allowing your heart to contract. He's also going to make you better able to spot inaccuracies in medical dramas by explaining how defibrillators work to reset the rhythm of your heart.
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Sydd Linden's profile photoVidSheridan's profile photoMichael M's profile photoOliver Isenrich's profile photo
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As someone with a heart murmur I would also like to know more about them..
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Your heart gets a lot of attention from poets, songwriters, and storytellers, but today Hank's gonna tell you how it really works. The heart’s ventricles, atria, and valves create a pump that maintains both high and low pressure to circulate blood from the heart to the body through your arteries, and bring it back to the heart through your veins. You'll also learn what your blood pressure measurements mean when we talk about systolic and diastolic blood pressure.
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Dave Cole's profile photoBobbie Knopick's profile photoIrreverent Monk's profile photoDenise Rich's profile photo
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+CrashCourse The heart is best described in three dimensions, to see the hearth from all angles helps people grasp how it works.
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In the second half of our look at the endocrine system, Hank discusses chemical homeostasis and hormone cascades. Specifically, he looks at the hypothalamus-pituitary-thyroid axis, or HPT axis, and all the ways your body can suffer when that system, or your hormones in general, get out of whack.
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+CrashCourse Thank you, now I know that part of my fibromyalgic inability to regulate body temp is once again due to a miscreant hypothalamus.
"Damn you, Infundibular Nuclei, damn you all to hell!"
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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.
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+CrashCourse can I have that LEGO Millennium Falcon when you're done with it? (Lol, I'm a huge LEGO geek.) :3
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Have them in circles
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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.
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+Harm Aouke Haaijer Oops! Forgot to do that! Fixed :)


-Nicole
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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.
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+RMoribayashi of course, maybe it's around 45% to 50% but there is no aggrement. it's ±50% ( ≈50% )
± or = approximately equal to
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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.
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+Christopher Fernandez Like that comment to get it noticed!
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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.
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Lapsis Azurite's profile photoSebastian Fernandez Alberdi's profile photoBobbie Knopick's profile photoOliver Isenrich's profile photo
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+Billybob Nerd Time what's your problem bruhhh
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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.
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Sebastian Fernandez Alberdi's profile photoAsta Muratti's profile photoMark Monyhan's profile photoJ Wash's profile photo
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Digging a bit myself, I found two different ideas tying dipoles to gravity.

One is a concept in gravitational physics involving the distribution of mass in a given object. In this case the dipole isn't a force, but a characteristic of the mass. It's not an idea unique inside or outside the US and is pretty uncontroversial. Nor is it some new super secret approach to gravity US students are unaware of. It's taught in several US undergrad physics programs I was able to find quite quickly. They even have FAQ pages with references explaining it.

The other use of dipole in reference to gravity that I was able to find refers to the electric universe theory which has been disproven in its many forms quite a number of times and has been directly addressed by Phil Plait himself on his Bad Astronomy blog at least once. It was a theory initially proposed by a Nobel Prize winner, Hannes Alfven, that nevertheless ventured into an area of science he didn't have a background in. His knowledge WAS solid enough to produce a hypothesis that at least passed the sniff test, but in the end several experiments and a good deal of analysis showed his hypothesis to be fundamentally flawed. The EU theory proponents that followed generally veered even further from reasonable hypothesis to the degree that it barely resembles Alfven's ideas and certainly steers a good deal further from experimentally provable.
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Hank calls in a friend to do his push ups for him today to explain how skeletal muscles work together to create and reverse movements. Hank and Claire also demonstrate the role size plays in motor units, the three phase cycle of muscle twitches, and how the strength and frequency of an impulse affects the strength and duration of a contraction. This episode also explains twitch summation, tetanus, and isotonic vs. isometric movements.
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Tayla Viego's profile photoim mad @ yu toob's profile photoAsta Muratti's profile photoChristopher Kecun's profile photo
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+Tayla Viego When exerting yourself, your muscles produce a substance called lactic acid when they respire, a significant build up of this substance causes fatigue.
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Story
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Six awesome courses on one awesome channel.
Introduction
John and Hank Green teach you U.S. History and Chemistry, Literature and Ecology, World History and Biology

A new episode of CrashCourse: Chemistry is posted every Monday and a new episode of CrashCourse: U.S. History is posted every Thursday.

CrashCourse has over 590,000 subscribers and 30 million video views.