Glow On: Crash Course Kids #20.2 - By Crash Course Kids
Transcript
| 00:09 | Let's continue our chat from last time about stars that | |
| 00:12 | are not you ? I mean the stars in our | |
| 00:15 | universe . We've already talked about what a star is | |
| 00:17 | a huge ball of hot gas that makes heat and | |
| 00:20 | light , basically they glow . But how do they | |
| 00:22 | glow ? And why do some stars seem to glow | |
| 00:25 | brighter than others ? Let's tackle question numero Uno first | |
| 00:33 | . How do they glow ? All stars create energy | |
| 00:36 | in their core through a process called nuclear fusion . | |
| 00:39 | Sounds super cool , right ? It is well , | |
| 00:41 | superhot actually , but you get the idea , it's | |
| 00:43 | needs . It's also way too complicated to explain in | |
| 00:46 | one video . So I'll just give you a really | |
| 00:48 | , really basic overview the temperatures and pressures inside a | |
| 00:51 | star . So great that nuclear fusion the same thing | |
| 00:54 | that powers hydrogen bombs is almost constantly happening at the | |
| 00:57 | center of a star . Most stars are made up | |
| 00:59 | of mostly two kinds of gases , hydrogen and helium | |
| 01:02 | . During nuclear fusion , hydrogen molecules , really tiny | |
| 01:06 | units of hydrogen smash into each other or fused together | |
| 01:09 | to create helium . The enormous amount of energy that's | |
| 01:12 | created as a result of this fusion then travels out | |
| 01:15 | towards the surface of the star as heat and light | |
| 01:17 | and gives the star it's glow . All stars go | |
| 01:20 | through this process to get their glow , but they | |
| 01:22 | don't all shine equally , leading us to our second | |
| 01:25 | question , Why do some stars glow brighter than others | |
| 01:29 | stars have different brightness ? Is there are two major | |
| 01:31 | things that astronomers look at when determining how bright a | |
| 01:33 | star is . It's true brightness and it's apparent brightness | |
| 01:37 | . Astronomers sometimes referred to a star's true brightness as | |
| 01:40 | its luminosity , luminosity is a measure of how much | |
| 01:43 | energy or light a star shines from its surface . | |
| 01:46 | Think of stars like light bulbs , light bulbs with | |
| 01:49 | higher wattage is , or more power glow brighter . | |
| 01:51 | Right . Same thing with stars , the more luminous | |
| 01:54 | or powerful a star is , the brighter it glows | |
| 01:57 | when measuring luminosity , astronomers are considering how bright the | |
| 02:00 | star is as if they were in space standing or | |
| 02:03 | I guess hovering right in front of it . That's | |
| 02:06 | why they call it true brightness . It's how bright | |
| 02:08 | the star really is , not just how bright it | |
| 02:10 | might look , depending on where you are . So | |
| 02:12 | how does the stars size factor in ? Some stars | |
| 02:15 | are really , really big and some are really , | |
| 02:18 | really well , not small but small Earth . So | |
| 02:21 | if it's bigger , it must glow brighter . Right | |
| 02:24 | ? Not necessarily smaller stars sometimes have more power than | |
| 02:27 | bigger stars . Just like smaller light bulbs can have | |
| 02:29 | more wattage than bigger . Light bulb size also isn't | |
| 02:32 | necessarily important when measuring the second thing that astronomers look | |
| 02:35 | at when determining a star's brightness , its apparent brightness | |
| 02:39 | . When we talk about apparent brightness , distance is | |
| 02:42 | a bigger factor than size , since astronomers can't really | |
| 02:45 | go into space to see those stars up close because | |
| 02:48 | , you know , they burn up and it would | |
| 02:49 | take too long to actually get to another star . | |
| 02:51 | They also measure how bright a star appears to us | |
| 02:54 | from a distance . This measure is called it's apparent | |
| 02:57 | brightness . So regardless of its size or its power | |
| 03:00 | , how near or far a star is to Earth | |
| 03:03 | plays a big part in how bright it appears to | |
| 03:05 | us . Not convinced . Let's take a look at | |
| 03:07 | two stars to see if the more luminous one also | |
| 03:09 | appears brighter to us . Earthlings . Well , mm | |
| 03:14 | hmm . First meet Beetlejuice . Beetlejuice is a star | |
| 03:19 | , one of the brightest stars in the night sky | |
| 03:21 | . In fact , Beetlejuice shines with around 100,000 times | |
| 03:24 | more luminosity or power than the sun . So you'll | |
| 03:27 | need some serious shades to look at this guy up | |
| 03:29 | close . But how does that compare to the sun | |
| 03:32 | ? The sun is a star we've all spotted from | |
| 03:33 | earth way more times than we've seen Beetlejuice . Since | |
| 03:36 | we have no problem locating it , it must be | |
| 03:38 | bigger than Beetlejuice , right , nope . I mean | |
| 03:41 | , don't get me wrong , the sun is huge | |
| 03:43 | . More than a million earths could fit inside it | |
| 03:46 | , but it's not so big when you compare it | |
| 03:47 | to Beetlejuice because Beetlejuice is gigantic , about 400 times | |
| 03:53 | bigger than the sun . But because Beetlejuice is located | |
| 03:56 | much farther away from us than the sun is , | |
| 03:58 | it appears less bright to us . If the sun | |
| 04:01 | was located that far away , you need a telescope | |
| 04:03 | to see it at all . Since it doesn't have | |
| 04:05 | as much power as Beetlejuice . So it's not the | |
| 04:07 | sun's size or power that makes it seem so big | |
| 04:09 | and bright to us on earth . It's because it's | |
| 04:11 | so close to us just 150 million kilometers away . | |
| 04:15 | So Beetlejuice is bigger and more luminous or has a | |
| 04:18 | higher true brightness than the sun . And you'd be | |
| 04:21 | able to tell that if you could look at them | |
| 04:22 | side by side , but the sun has a higher | |
| 04:24 | apparent brightness to us on Earth because it's so much | |
| 04:27 | closer . So let's call this brightness battle a tie | |
| 04:34 | to recap . Stars glow as a result of the | |
| 04:36 | energy created in their core by nuclear fusion . That | |
| 04:39 | energy travels outward to the surface of the star where | |
| 04:42 | it's seen and felt as light and heat . All | |
| 04:44 | stars glow because of nuclear fusion , but they don't | |
| 04:47 | glow equally . The amount of power A star has | |
| 04:49 | and its distance from us both influence its brightness . | |
| 04:52 | On that note , I think it's time for me | |
| 04:54 | to do some stargazing of my own astronomer Sabrina's out |
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Glow On: Crash Course Kids #20.2 is a free educational video by Crash Course Kids.
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