Light: Crash Course Astronomy #24

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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Chapters:
Introduction 00:00
Light is a Wave 0:31
Electromagnetic Spectrum 1:32
How is Light Made? 3:19
Atomic Structure 4:47
Spectroscopy 7:14
Redshift vs Blueshift 8:26
Review 9:50

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PHOTOS/VIDEOS

[Schurfable]

I feel more enlightened after watching this. It really shed some light on this topic. Perhaps I am slightly brighter today than I was yesterday. It kinda turns me on

[ArakkoaChronicles]

That must have been the best explanation of electron shells I heard so far.

[InfraRaven]

I love this show. Thanks to everyone who keep this going.

[jgmeng]

This just became my most favorite episode of all crash course series. Analogies are perfect. So simple to understand.

[simonh]

You just did an entire video on light without mentioning photons. I'm impressed.

[leukosanthemon]

Been watching CrashCourse since highschool and now that I'm a teacher, I still love coming back to these videos :)

[TheAnnihilator]

MOAR.
Just binge watched all episodes(up till light, which is the last episode as of now), took notes, googled stuff I didn't understand, fast forwarded stuff which I knew well and re-played stuff that was awesome.
WANT MOAR!

Awesome job :D

[rvymvn]

This episode was so awesome.
Well.... They're all awesome...







But this episode was awesome

[Xenro]

Omg I want that periodic table at 5:22 as a poster on my wall... Make it happen plesh!!!!
P.S: You explain how light is emitted faster than my physics teacher did... OVER ONE YEAR .__.

[AdvosArt]

You just said everything I was thought in a month

[rexhex]

Man science is so much more fun when you aren't forced to do it for school.

[camavita]

This ten-minute video made me understand atomic structure where two semesters of chemistry failed. Thank you, Crash Course! Love what you do!

[TheHelghast]

This was the hardest to grasp episode yet, but a fantastic and critical one. Also the Green brothers on the moped was awesome.

[nurjakhon]

One of the best educational videos I've ever seen. Love you, CrashCourse team!

[moiquiregardevideo]

What is (visible) light? It is a wave, period. At last, somebody who can explain this clearly. Inspired by the video from Phil Plait, I would highlight the following:

Photon:
Each photon is an oscillating wave which push and pull the electric field as it propagate in free space - creating local increase and decrease of electric field pressure - the same way as sound wave propagating by pushing and pulling on air molecules.

Fourrier Series for light
Our eye perceive exactly one octave, the red being equivalent to bass and blue equivalent to higher pitch instrument. According to Fourrier series, any wave that is not sinusoidal (produced by an object circulating around a sphere) can be simulated by adding a few sinusoidal wave which have integer multiple of the fundamental. For example, a square wave at 60 Hz can be simulated as follow:
a*60 Hz + b*180 Hz + c*180 Hz
where a, b and c is the intensity (how loud the volume is set) for each of these frequency. Changing these coefficients (and adding also the even numbered) would produce saw tooth or any other waveform. Brief, when a wave is not a pure sinusoidal shape, then it contains harmonics, which is small amount of wave with frequency exactly double, triple, etc.
The color detectors in our eye may react when a wave of exactly double or half the frequency hit them. That may explain why light going up after blue appear as purple ; the red detector become activated.

What are electrons
Atoms are not like as small solar system with proton/neutron in the center and electron rotating around like the planets around the sun. The electrons are "something" which wiggle randomly "around" very fast, like a bouncing rubber ball inside a metal or glass sphere .

Humming bird vision
The uncertainty principle is related to our incapacity to figure out how much faster this "thing" called electron oscillate compared to our measurement devices. Predicting where is an electron with the present technology is like asking to a human to predict the location of the wing of a hummingbird. We just see a blurry cloud. But a hummingbird eye and brain is about 10 time faster than our visual system, so they see the beating of their wing when looking at them self in a mirror.

Dangerous cliff
Our distant ancestors, the Jellyfish, wisely selected the visible light to get the 4K clear vision that we enjoy today. Like all engineering decision, this choice represent a compromise between conflicting factors. Using a lower frequency, like the infrared, give more blurry picture, as any desert snake can tell you. Using higher frequency gives more clear picture, but can be used only on clear day time. Furthermore, the ultraviolet light (and X ray and gamma ray) is ionizing. It's energy is so high that electrons are kicked off atom and long molecules chain break apart. With UV light, the DNA data bank receive kicks in the teeth and cells forget how to behave politely in pluri-cellular society, which is perceived on the macroscopic scale as cancer.

[matthewhaley]

I'm excited about the next episode! Distance throughout the universe has always fascinated me. Thats for your expertise, Phil!

[lythalmind]

my mind is always blown when I learn how it is we know things about our universe. Science is awesome

[anisilva]

I have been using Crash Course videos in my daughter's history, science and A&P classes for the last two years. This teacher is the best. He explains the information about light with just the right balance of energy and calm (he is very easy to follow, others tend to go too fast for even me to understand 🤯). Well done.

[Halpok]

It's insane thinking about how we are just extreme luck and that if a certain chemicals never existed we may never of existed. Keep up the good work Crash Course :3

[zavier]

Best episode of the whole series! I was totally blown away!