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Introduction to Middle school Earth and space science

In this course, you’ll explore the wonders of our planet and the universe beyond. From the water cycle to plate tectonics, learn about the different processes that shape our world. Created by Iman Howard.

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  • blobby green style avatar for user sarahtime030
    If scientists discovered for a fact that dark matter and energy is real would we have a hypothesis on how it would affect our universe? If so how would it?
    (8 votes)
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    • female robot amelia style avatar for user Johanna
      We actually have observed both dark matter and dark energy! We first discovered dark matter from its gravitational effects on galaxies. People calculated that galaxies were spinning so fast that the gravity from their visible matter wasn’t enough to keep them from flying apart. That means there must be some mass that isn’t just regular matter: dark matter.

      Since (as far as we can tell) dark matter only interacts with the rest of the universe via gravity, that’s what we have to use to study it. Another gravitational effect is gravitational lensing. This happens when light bends when it travels around massive objects. General relativity predicts gravitational lensing, and we first confirmed it by measuring where stars around the sun appeared during solar eclipses. Their light does appear to come from different directions when the sun is near them. For dark matter, we also observe that the light coming around it appears distorted as well.

      Dark energy makes the expansion of the universe speed up. We’ve observed the light from distant stars and discovered that the further a star is from us, the faster it appears to be moving away from us. This happens because space itself is expanding. We know the universe is expanding, but for a while we didn’t know if its expansion was getting slower or faster with time, or if it was just expanding at pretty much the same rate.

      Gravity makes things with mass pull together. Specifically, it makes massive things that are moving apart (like they are in our expanding universe) start to move apart more slowly and eventually start moving together. People thought, then, that gravity might be slowing its expansion down. So, they set out to observe more distant stars again to test this prediction.

      The universe’s expansion wasn’t slowing like they thought, though! It was speeding up. We call the thing that counteracts gravity (over very long distances) and makes the universe expand faster and faster dark energy.

      Does that answer your questions at all? There’s still a lot we don’t know about dark matter and energy, so people are studying them!
      (5 votes)
  • blobby green style avatar for user gabryelelise
    do you believe that there are other sources of life on different planets in our solar system
    (6 votes)
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    • aqualine ultimate style avatar for user Mark
      The only evidence that we have of potential life elsewhere in the solar system comes from Martian meteorite "Allan Hills 84001". It's a rock from Mars that appears to contain fossilized bacteria. Most scientists reject the hypothesis that the structures in the meteorite are fossils and instead believe that they were produced abiotically. But, it is still debated and at this point we don't know for sure.
      (2 votes)
  • duskpin seedling style avatar for user DestineeM
    What was the first other planet found other than Earth, it seems that there are so many out there and it's just crazy!
    (6 votes)
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    • aqualine ultimate style avatar for user Mark
      The first planets to be discovered were Mercury, Venus, Mars, Jupiter, and Saturn. They were discovered more or less at the same time because they all can be seen with the naked eye. Uranus and Neptune weren't discovered until after the invention of the telescope.
      (2 votes)
  • blobby green style avatar for user JaisonE
    why didn't the sun cool down
    (5 votes)
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  • starky tree style avatar for user ∞§§¶™
    Is Mars in livable conditions yet?
    (3 votes)
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  • male robot hal style avatar for user prehistoric-rishi
    What would happen if Jupiter hit the sun?
    (4 votes)
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  • duskpin sapling style avatar for user BlossomRose26
    Hi!
    I'm really excited about this (Earth and Space Science)
    I am especially curious on black holes and am wondering if there is anything called a white hole. I would love to learn more about space science (astronomy) and dark matter. And really, about that season thing? I'm really caught by that hook. 👌🏻👍🏻😊
    (2 votes)
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  • blobby green style avatar for user Milagro Silva
    How much years have earth been in the solar system
    (4 votes)
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    • blobby green style avatar for user Kenobi
      Scientists have analyzed Earth’s crust, its rocks, and those of the Moon, and several meteorites, and concluded that the Earth is around 4.54 billion years old, with a margin of error of about 1%. When it comes to the Moon, it is speculated to be 4.53 billion years old.
      (2 votes)
  • aqualine ultimate style avatar for user Ali R A.K.A CR7 BIGGEST FAN
    do u beileve that there is other alive things on other planets outside the solar system
    (2 votes)
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  • piceratops seedling style avatar for user lcordial01
    what if we are wrong, what if the space between the planets were moving?
    (1 vote)
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Video transcript

- Hi everyone. Sal Khan here and I'm with Iman Howard, who is our manager for all of our stem content on Khan Academy. And we wanted to welcome you to the Middle school Earth and Space Sciences course. Iman, why should folks be excited about this? - So Middle school Earth and Space Science is really exciting because it's one of those areas of science that answers what's happening in our universe. And then like when you dig in, you're like "What is happening in our universe? This is why we have seasons." And so we start like really big, we go all the way to outer space and we figure out sort of earth's position in our solar system and the relationship to gravity and our inner planets and our outer planets. And then we keep digging in and we finally figure out how Earth's position answers seasons. It's not because we get closer to the sun or how based on earth's position, we look up at the moon and you'll see a lunar eclipse or how you don't look up and look at a solar eclipse, like seriously don't look up because it'll hurt your corneas. And then we keep going and we talk about water and how the same water that you're drinking right now is the exact same water that dinosaurs drink. And then we get into the rock cycle and we figure out why mountains are here and how we're moving right now. Literally the plates below us are moving and how at one point we could walk across all the way from the US to Africa and how plate tectonics really changed that. And then finally, finally, we talk about us. We talk about us on this planet and how there's so many amazing resources here and how well how we use them really impacts the earth and how that could impact our climate. And really awesome things that you can do as a learner to change all that and make this earth really awesome. What are you excited about, Sal? - Well, I'll just double down everything you said and I like how you said we're gonna dig into it 'cause it's very appropriate pun for earth, earth and space. This starts to answer the questions of, the from the cosmos to earth. Over billions of years, as you mentioned, the earth is alive in certain ways with the plates are still moving it's active and we should say at least, and you know we are part of the earth. Your point, the, the water in our bodies the air that we breathe, it's the same water and earth that has been been here and the air for billions and billions of years. So to be able to actually understand that it, it actually gives me, gives me goosebumps. So I think folks will be very excited about this course. - Absolutely. (upbeat music)