How to Estimate Distances (by Using Your Thumb and Eyes)

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Hikers, photographers, hunters, golfers, home astronomers, and nature lovers, if you have ever wondered how far away you are from a given object, estimating that distance may be easier than you realized. The length of your arm is roughly ten times the distance between your eyes. With this fact in mind, you can measure the approximate distance between yourself and almost any object.

Part 1
Part 1 of 2:

Aligning Your Body

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    To estimate distance, you need a clear line of sight. Try to stand in a high place, like atop a hill or a few floors up in a building. If this isn’t possible, try to find a spot where no other objects are in between you and the object you are focusing on.
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    Here are some standard lengths that may help you:
    • Most average-sized cars are between 12 and 15 feet long.
    • Mailboxes are usually around 1.5 feet long.
    • Mature tree trunks are typically between 1 and 2 feet wide.
    • The standard length of a trailer pulled by a semi-truck is 50 to 65 feet long.
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    Aim your arm toward the object, and try to keep it as straight as possible. Point your thumb up. [1]
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    Keep standing as still as possible.
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    Try to keep your head and arm perfectly still. [2]
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Part 2
Part 2 of 2:

Calculating the Distance

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    Keeping perfectly still, close your left eye and look through the right eye. Your thumb will appear to have “jumped” to the left. This “jumping” phenomenon is called “parallax.”
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    Did your thumb jump 3 times the length of the object? Half the length? Keep this number in mind. For example: [3]
    • If your thumb jumped 3 times the length of a building that you believe is 100-feet-long, then it jumped 300 feet.
    • If your thumb jumped half the length of a 14-foot-long car, then it jumped 7 feet.
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    This will give you the approximate distance you're looking for. For example: [4]
    • If your thumb jumped 3 times the length of a 100-foot building, or about 300 feet (91 m), then you would multiply 300 by 10 to conclude that the building is about 3,000 feet (914 m) away from you.
    • If your thumb moved half the length of a 14-foot-long car, or about 7 feet (2 m), then you would multiply 7 by 10 to conclude that the car is about 70 feet (21 m) away from you.
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    How might astronauts use parallax?
    Community Answer
    To find out how far away planets and stars are, or find the angle between two objects and find the distance between them.
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      References

      1. ↑ https://www.pbs.org/wgbh/nova/teachers/activities/pdf/2313_threemen_02.pdf
      2. ↑ https://www.pbs.org/wgbh/nova/teachers/activities/pdf/2313_threemen_02.pdf
      3. ↑ https://www.mathsisfun.com/measure/estimate-distance.html
      4. ↑ https://www.mathsisfun.com/measure/estimate-distance.html

      About This Article

      Article Summary X

      If you’ve ever wondered how far away you are from a given object, you can estimate the distance with your thumb and eyes. Start by holding your right arm out in front of you, pointing it toward the object you’re measuring to. Point your right thumb up and close your right eye. Keeping as still as possible, line up the left edge of your right thumb with the right edge of the object. Then, close your left eye and look through your right eye, which will make your thumb appear to have moved to the left. Estimate how far it looked like your thumb jumped. For example, if it looked like it jumped 3 times the length of a building that you think is 100-feet-long, then it moved 300 feet. Next, multiply the number from the jump by 10 to get the approximate distance you’re looking for. So, if your thumb jumped 300 feet, you can conclude that the building is about 3 thousand feet away from you. To learn how to calculate the length of basic objects, keep reading!

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