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Course: Middle school Earth and space science > Unit 1
Lesson 1: Earth's place in the universeEarth's place in the universe
Humans have used models to understand Earth's place in the universe. The geocentric model, placing Earth at the center, was replaced by the heliocentric model, with the sun at the center. This change better explains the movement of celestial bodies and shows that Earth's rotation causes the sun's apparent motion. Created by Khan Academy.
Want to join the conversation?
- why does the sunrise in the east and set in the west?(18 votes)
- This is a fantastic question! The Earth spins (or rotates) on its axis toward the east. Since it spins towards the east, the Sun appears to rise in the east and set in the west.
Fun fact: This is also why it looks like the moon, planets, stars, and other visible parts of the solar system rise in the east and set in the west!
Fun fact 2: Venus rotates backwards (which is also known as retrograde motion), so if you stood on Venus, the sun would actually rise in the west and set in the east.(65 votes)
- What happens if the Earths coarse trajectory changed and it went out of place, impacting on the circle around the sun. Will it change the position of the solar system.(16 votes)
- i mean it might attract other planets a tiny bit because of gravity but not enough to do any big changes(1 vote)
- I saw the solar eclipse at 95%!,☀️(7 votes)
- what comes after the universe I mean like it can't be that there is literally nothing after the universe and if there is no end then how big is the universe(4 votes)
- multiverse? Just a theoretical answer. Has not been proven right yet(4 votes)
- how thin is the earths crust(3 votes)
- The Earth's crust is over 43 miles thick. That is 3.89E^6 (3,892,107.169) oreo cookies thick. That's a lot of cookies.(6 votes)
- What impact does the black hole in the middle of our galaxy have on our earth, and other planets around it?(2 votes)
- The whole solar system actually orbits that black hole (Sagittarius A*)! It’s so far away from us that it has very little gravitational effect on our solar system besides that, though.
Does that help?(6 votes)
- what was the point of humans have a models made to see how the earth workes or how it lookes in the space.(4 votes)
- What is the NEARST star from earth and would it take your whole life to get there(1 vote)
- The nearest star from Earth is Proxima Centari, which is 402 light years away. If we were to travel 17.3km/s, it would take us 73,000 years to arrive. Considering a 25 year generation, that would mean it would take 2,920 generations to arrive.
So,no, it would not take your entire life to get there, it would thousands of lifetimes.(6 votes)
- Ok deep question here. Isn't it a little conceited to think that the big bang occured in our area of space? For instance space is ever expanding with no apparent end in signt and we ask ourselves what happened before the big bang? Why not look to the other galaxies that may be older than us to answer that question? I have never heard about any evidence stating that the big bang was only for us or at least what started everything only that it created our sun and solar system but what if it was a reaction to other planets and galaxies already existing? I need to learn more about this subject. Upload more cosmology videos please...(3 votes)
- The big bang wasn't just an explosion. it was a chain of events happening all over the universe.(1 vote)
- Question... How far is the nearest black hole to earth?(3 votes)
- Gaia BH1 is 1560 light years away from earth, and was discovered by the European space agency.(1 vote)
Video transcript
- [Narrator] Hello, everyone. Today, we are going to be talking about Earth's place in space. So for as long as there have been humans, we've been looking up at the stars, and wondering about our
place in the universe. Our understanding about
this has improved over time, and we have developed models that can help us understand
something as vast as space. Now, models are just a way of
representing a system of ideas that help us identify and
understand patterns that we see. Models are a tool that can explain, and predict what we see in
the world and space around us. And as we gain new information,
we can update our models. So what kind of model might we construct about how Earth interacts with
other bodies in the universe? To begin with, every day, we can see the sun rise in
the east, and set in the west, and other objects in the sky
follow a similar pattern. It was logical then for early models to consider the Earth
as a stationary object, around which all of the universe revolves. This is called a geocentric model, geo for Earth, and centric for center. And this geocentric model was quite good at explaining a lot of the
things that we see in the sky, like the apparent motion
of the sun and the stars. But there were issues with
this geocentric model. For example, the motions of
other planets in the sky. A planet like Jupiter might
sometimes move backwards in the opposite direction, which isn't really very well explained by this geocentric model. Now, when a model doesn't match
our observations like this, we can add new pieces
to improve the model. So astronomers working
with the geocentric model did this by adding smaller cycles within the planets'
orbits around the Earth. Adding these cycles did help
match the geocentric model to the observations, but there were many of
these cycles required, and there wasn't a good explanation for why these cycles existed. And there wasn't very
much reasoning for them, and they made the model very complicated, and not particularly useful. Let's pause and talk a
little bit about motion, specifically apparent versus actual. Imagine you're sitting in a car, and driving through a forest. To your perspective, as
you look out the window, the trees seem to be whizzing by, but trees, of course,
are rooted to the ground. It's actually you that are moving relative to the surface of the Earth. This is the difference between
apparent and actual motion. So back to our geocentric model. Another way to explain some of the issues with a model like the geocentric model, besides adding evermore
complicated features to it, is to in fact, just come
up with a new model. And this is what astronomers did. The new model that was proposed to replace the geocentric model
was the heliocentric model. In this model, the Earth
and all the other planets actually revolve around the sun. Helio means sun. This heliocentric model
didn't need complicated and unexplained cycles to explain the way the other
planets moved across the sky. It was an expected outcome
of the planets' orbits. Now you may be wondering, in this model, the sun is stationary. So why does it seem to be moving across the Earth's sky each day? This is actually also easily explained, because the motion of the sun in the sky is not actual motion,
it is apparent motion. Not only is the Earth
revolving around the sun, revolving means orbiting, but the Earth is also
spinning on its own axis. And so as the surface of the Earth moves with its spinning motion, it makes it appear as if the
sun is moving across the sky. The spinning of the Earth actually explains why celestial objects appear to rise and set
over the course of a day, while the revolution, or orbit, around the sun explains
the motion of those objects over the course of a year. It's important to remember that
while the heliocentric model does a better job of explaining and predicting our solar system, which is what we want models
to do, it is still a model, and not a perfect recreation of reality. For example, while the heliocentric model considers the sun as stationary, we know now that the sun
is actually just one star of many billions orbiting
the center of our own galaxy. And so the sun, along with
the rest of the solar system, is in fact, moving. To summarize, in this video, we talked about how we can use models to help us understand
what we see in the sky, and Earth's place in space. As we learn more, we improve our models, and we can develop new
ones that do a better job of explaining our observations, and predicting the world around us, such as the change from a geocentric model to a heliocentric model. The Earth then is a planet
that orbits the sun, like the other planets
of the solar system. And the sun appears to
move across the sky, because the Earth spins on its axis. Thanks for watching, and I hope you learned a
little bit of something.