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What I want to do in this video is explain what parallax, what parallax actually is and then then

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try to visualize what the parallax would be like in the context of observing relatively nearby stars, and then in the next video

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we're going to think about how we can use the parallax of nearby stars to figure out how far they actually

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are away from us. So parallax really is just the apparent change in the position of something based on

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a different line of sight. So when you see that and you just look at, so while you are looking at a car

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you are going to see that depending on how far different things are from you it looks like they're moving

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relative to each other. Right now I am looking at my computer monitor and if I move my head around

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or shake my head around it looks like the wall behind the computer monitor is moving relative to the

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computer monitor. We've all experienced this. Let's think about what parallax means when looking at stars.

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So let me draw, let me draw the sun here, and obviously none of this is drawn to scale. So let me draw

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the sun here and let me draw the earth at some point in its orbit around the sun, and we're going to

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pretend that we're looking from above the solar system. The earth will be rotating, the earth will be

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rotating in this direction right over here; and let's say that the star we care about, the start that

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we care about is right over here. The star that we care about is right over here. Obviously, clearly not

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drawn to scale. And what we're going to do is we're going to wait until the point in the year, so the

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point in our orbit around the Earth, so that right at dawn, so we're sitting right here on the surface

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of the earth and to simplify things we're on the equator and let's say that this is the stars roughly

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in the plane of our solar system. So we're sitting right here, we're sitting right here, on the equator, and

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then right at dawn, right when the first light of the sun, right when the first light of the sun begins

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to reach me; remember that right now the sun is lighting up this side of the earth. So right when the

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first light of the sun is reaching me, I'm looking, I'm looking straight up. So if I look straight up