Distance

  

One of the greatest topics to understand the science of where we live is distance.  Your first step is here.

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 Astronomical units are a useful measure for distances in our solar system, while light years are more practical for distances to the stars. The nearest star system, Alpha Centauri, is seen from Saturn in this image from NASA’s Cassini spacecraft. Credit: NASA/JPL/Space Science Institute

Cosmic Distances

1. By Preston Dyches  Feature Magazine| May 18, 2020
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3. The space beyond Earth is so incredibly vast that units of measure which are convenient for us in our everyday lives can become GIGANTIC. Distances between the planets, and especially between the stars, can become so big when expressed in miles and kilometers that they're not understood. So for universe distances, we switch to whole other types of units: astronomical units, light years and parsecs.
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5. Astronomical units, abbreviated AU, are a useful unit of measure within our solar system. One AU is the distance from the Sun to Earth's orbit, which is about 93 million miles (150 million kilometers). When measured in astronomical units, the 886,000,000-mile (1,400,000,000-kilometer) distance from the Sun to Saturn's orbit, is a much more manageable 9.5 AU. So astronomical units are a great way to compress truly astronomical numbers to a more manageable size. 
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7. Astronomical units also make it easy to think about distances between solar system objects. They make it easy to see that Jupiter orbits five times farther from the Sun than Earth, and that Saturn is twice as far from the Sun as Jupiter. (This is because, technically, you're expressing every distance as a ratio of the distance from Earth to the Sun. Convenient!)
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9. The animated video illustrates how far a light second, minute and year are. Stop the video to make notes.

10. For much greater distances — interstellar distances — astronomers use light years. A light year is the distance a photon of light travels in one year, which is about 6 trillion miles (9 trillion kilometers, or 63,000 AU). Put another way, a light year is how far you'd travel in a year if you could travel at the speed of light, which is 186,000 miles (300,000 kilometers) per second. 
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12. (By the way, you can't travel at the speed of light [[[more elsewhere]]]as far as we know, but that's a whole other story...) 
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14. Like AU, light years make astronomical distances more manageable. For example, the nearest star system to ours is the triple star system of Alpha Centauri, at about 4.3 light years away. [[more more]] 
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That's a more manageable number than 25 trillion miles, 40 trillion kilometers or 272,000 AU.

1. source      pagetop      Distance continued here

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