Estimating the Diameter of the Moon Using a Pencil - Simple Physics Problem

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SUMMARY

The discussion focuses on estimating the diameter of the Moon using a pencil as a simple physics problem. The method involves holding a pencil at a distance of approximately 15 cm from the eye to block the Moon, which is 3.8 x 10^5 km away. By measuring the pencil's diameter at 1.5 cm (or 1.5 x 10^-5 km), participants suggest applying similar triangle theory to derive the Moon's diameter. This approach effectively utilizes basic geometric principles to solve the problem.

PREREQUISITES
  • Understanding of similar triangles in geometry
  • Basic knowledge of measurements in both centimeters and kilometers
  • Familiarity with the concept of angular size
  • Ability to perform unit conversions
NEXT STEPS
  • Research the application of similar triangles in real-world scenarios
  • Learn about angular diameter and how it relates to distance
  • Explore basic physics principles related to light and vision
  • Investigate methods for measuring astronomical distances
USEFUL FOR

This discussion is beneficial for students new to physics, educators teaching basic geometry, and anyone interested in practical applications of measurement and estimation in astronomy.

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im new to the physics world and know this is probably an easy problem but i don't know where to start

Hold a pencil in front of your eye at a position where its end just blocks out the moon. Make approprite measurements to estimate the diameter of the moon, given that the earth-moon distance is 3.8x10^5km.

i figured that you prob had to measure the end of a pencil which i measured about 1.5 cm which is 1.5x10^-5km but i don't really know what to do from there.
 
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k_yup said:
im new to the physics world and know this is probably an easy problem but i don't know where to start

Hold a pencil in front of your eye at a position where its end just blocks out the moon. Make approprite measurements to estimate the diameter of the moon, given that the earth-moon distance is 3.8x10^5km.

i figured that you prob had to measure the end of a pencil which i measured about 1.5 cm which is 1.5x10^-5km but i don't really know what to do from there.

How far away was the pencil from your eye?
 
about 15cm
 
so use simular triangle theory?
 
k_yup said:
so use simular triangle theory?

Yes, that would do it nicely.

Sorry for late reply I guess I missed it last night when I scanned the board.

Good luck.
 

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