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  • [ ♪ Intro ]

  • People have been awed by the sky ever since there were people,

  • and today's astronomers are heirs to that millennia-long tradition.

  • But what's surprising is that the way modern researchers study the sky

  • hasn't really changed in the last few centuries.

  • Sure, our methods have gotten better, and there's the odd cosmic ray to keep things interesting.

  • But for the most part, astronomers still study things by analyzing their light,

  • in other words, by looking at them.

  • They look at stars.

  • They look at galaxies.

  • They look at empty space.

  • They even look at dark matter, and you can't see dark matter!

  • Still, in the end, light is all astronomers need to consistently blow everyone's minds,

  • and there are three main ways they use it.

  • The most obvious way is just taking pictures of things,

  • whether in visible light or another wavelength like infrared.

  • Essentially, light comes into a camera, and the camera spits out some kind of picture.

  • This technique is a major way we study things like Saturn,

  • Pluto's famous heart, and even distant planets.

  • But it's not just about collecting pretty pictures.

  • Results from direct imaging build off each other just like any other scientific method.

  • For example, besides helping us understand Pluto's heart,

  • this method is also a big reason why we don't call Pluto a planet anymore.

  • That argument hinged on what else we directly saw in its orbit.

  • There is a lot you can't see just by looking straight at something, though,

  • so astronomers have also had to develop other techniques.

  • Their second trick is investigating polarization, or how light waves wiggle, or oscillate,

  • as they travel through space.

  • Generally, light from stars and most other sources starts out randomly polarized,

  • oscillating in all different directions.

  • But a few things can change that, like if a star is spinning really quickly,

  • if light goes through certain kinds of gas clouds, or if a star has a magnetic field.

  • These are all things that would be hard or impossible to pick out through more direct imaging,

  • so by measuring light's polarization, scientists can research things that would otherwise be invisible.

  • They study polarization by stretching long, thin strips of molecules across something like a lens,

  • making a filter that lets through some polarizations and not others.

  • Between these effects, astronomers have measured the magnetic fields of planets, the Sun, nebulas,

  • interstellar dust, pulsars, galaxies, the list goes on and on.

  • And these numbers aren't just for funsies.

  • Since magnetic fields come from moving charged particles,

  • those measurements tell us how matter and the charges in it are distributed throughout the universe.

  • Polarization measurements can also produce some of the most beautiful images in all of science,

  • like this stunning visual of the Milky Way's magnetic field,

  • where the colors tell you about its strength and the lines tell you about the polarization direction.

  • Most astronomical journals aren't dominated by direct observations or polarization measurements, though.

  • They're all about colors.

  • Lots and lots of colors.

  • There are a few types of astronomy like this, and they're all fundamentally based on studying

  • the colors that enter a telescope instead of the full picture.

  • One method comes from black-body radiation.

  • The hotter something is, the more randomly its atoms move, and the more light they give off

  • especially at higher energies.

  • Measurements of something's black-body radiation spectrum, then, tell us about how hot it is.

  • Stars' light usually peaks somewhere in visible light,

  • whether that's red for the coolest stars or blue for the hottest.

  • But things like the accretion disks around black holes, where gas is falling in, are hotter than the hottest stars,

  • and we know that because they emit lots of x-rays.

  • Empty space, on the other hand, is much colder.

  • And, again, we know because of its black-body spectrum, called the Cosmic Microwave Background.

  • So just using light, we're able to get a pretty good idea of the temperature of things,

  • no thermometer required.

  • A second way astronomers use color is through spectroscopy.

  • Every atom and molecule absorbs and emits light from some colors much better than others.

  • And after years of study, scientists have figured out how many of those particles behave.

  • They can even graph their light patterns on a chart, kind of like a fingerprint.

  • So when they get new data from stars or interstellar dust or extrasolar planets,

  • they can figure out what the objects are made of just by matching up sets of lines.

  • Well, almost.

  • Often, when we're studying really distant objects, their spectral lines aren't the right colors.

  • They're usually redder than we'd guess or sometimes they're bluer.

  • And that's because of Doppler shifts, another one of the most fundamental tools in observational astronomy.

  • Light gets stretched or compressed by movement, and the amount it's distorted

  • tells you how fast it's moving toward or away from you.

  • Doppler shifts were used by Edwin Hubble to discover the universe is expanding,

  • they've been used in all sorts of ways to infer the existence of dark matter,

  • they've revealed hundreds of exoplanets, and they've been used for everything in between.

  • The fact that we've been able to do so much with light is pretty mind-blowing.

  • And it also helps explain why, as astronomers discover different ways of exploring the universe,

  • like gravitational waves and neutrinos, they've been so excited.

  • We've been using nothing but light for hundreds and hundreds of years.

  • Imagine what we're going to be able to do learn with something new.

  • If you want to learn even more about those gravitational waves

  • and what new things we might be able to learn from them,

  • you can watch our episode about it.

  • And as always, thanks for watching this episode of SciShow Space!

  • [ ♪ Outro ]

[ ♪ Intro ]

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為什麼天文學自20世紀以來沒有真正的改變? (Why Astronomy Hasn't Really Changed Since the 1900s)

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    林宜悉 發佈於 2021 年 01 月 14 日
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