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Science & Technology
Light seconds, light years, light centuries: How to measure extreme distances
lesson duration 05:29
3,245,748 views
3,186,231 views
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3,065,698 views
3,042,928 views
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2,306,911 views
The oldest living things in the world
lesson duration 06:10
2,197,004 views
2,195,407 views
2,175,521 views