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Video: How do we measure distance in the universe? 

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Video: How do we measure distance in the universe? 

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Light seconds, light years, light centuries: How to measure extreme distances - Yuan-Sen Ting

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VIDEO: Making Models: A Solar System Pocket Model 

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VIDEO: Making Models: A Solar System Pocket Model 

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Video for instructions

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Exploring the Solar System: Pocket Solar System | NISE Network

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End of the Unit Project

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Top 3 Space Agencies You've Never Heard Of

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Rocket Science: How Rockets Work - A Short and Basic Explanation

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What is a light year?
Read the article and answer the following questions:
1. What is a light year?
2. What is the nearest large galaxy to us and how far is it?
3. What does a light year measure?
4. What is the speed of light and what does it mean?
5. What does the following sentence mean: "We always see the Sun as it was about 8.3 minutes ago". Explain.
6. In 2016, NASA's Hubble Space Telescope looked at the farthest galaxy ever seen, called GN-z11. It is 13.4 billion light-years away, so today we can see it as it was 13.4 billion years ago. Why is this important to humanity? Explain.

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For most space objects, we use light-years to describe their distance. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km). That is a 6 with 12 zeros behind it!

Looking Back in Time

When we use powerful telescopes to look at distant objects in space, we are actually looking back in time. How can this be?

Light travels at a speed of 186,000 miles (or 300,000 km) per second. This seems really fast, but objects in space are so far away that it takes a lot of time for their light to reach us. The farther an object is, the farther in the past we see it.

Our Sun is the closest star to us. It is about 93 million miles away. So, the Sun's light takes about 8.3 minutes to reach us. This means that we always see the Sun as it was about 8.3 minutes ago.

The next closest star to us is about 4.3 light-years away. So, when we see this star today, we're actually seeing it as it was 4.3 years ago. All of the other stars we can see with our eyes are farther, some even thousands of light-years away.

Stars are found in large groups called galaxies. A galaxy can have millions or billions of stars. The nearest large galaxy to us, Andromeda, is 2.5 million light-years away. So, we see Andromeda as it was 2.5 million years in the past. The universe is filled with billions of galaxies, all farther away than this. Some of these galaxies are much farther away.

In 2016, NASA's Hubble Space Telescope looked at the farthest galaxy ever seen, called GN-z11. It is 13.4 billion light-years away, so today we can see it as it was 13.4 billion years ago. That is only 400 million years after the big bang. It is one of the first galaxies ever formed in the universe.

Learning about the very first galaxies that formed after the big bang, like this one, helps us understand what the early universe was like.

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A light-year is the distance light travels in one Earth year. Learn about how we use light-years to measure the distance of objects in space.

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Are We Made of StarDust? (Animated Story)