How Did Roemer Measure the Speed of Light Using Jupiter's Moons?

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SUMMARY

Roemer measured the speed of light by observing the delays in the eclipses of Io, one of Jupiter's moons, which were delayed by 22 minutes over a six-month period due to Earth's orbital position. By calculating the additional distance light must travel when Earth is at its farthest point from Jupiter, using the average radius of Earth's orbit (1.50 x 108 km), one can derive the speed of light. This method established a foundational understanding of light's finite speed based on astronomical observations.

PREREQUISITES
  • Basic understanding of orbital mechanics
  • Familiarity with astronomical units and distances
  • Knowledge of light speed calculations
  • Understanding of time dilation and its effects in astronomy
NEXT STEPS
  • Calculate the speed of light using Roemer's method with provided data
  • Explore the implications of light speed on astronomical observations
  • Study the historical context of Roemer's findings in the development of physics
  • Investigate modern methods of measuring light speed, such as laser interferometry
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Astronomers, physics students, educators, and anyone interested in the historical methods of measuring astronomical phenomena.

dekoi
As a result of his observations, Roemer concluded that eclipses of Io by Jupiter were delayed by 22 min during a 6 month period as the Earth moved from the point in its orbit where it is closest to Jupiter to the diametrically opposite point where is is farthest from Jupiter. Using 1.50 x 10^8 as the average radius of the Earth's orbit around the Sun, calculate the speed of light from these data.
I have absolutely no idea how to start this. Please give me some suggestions.
Thank you.
 
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First ask yourself how much further the light has to travel when the Earth is furthest away from Jupiter compared to when it was closest to Jupiter. (Note that your value for the average radius of the Earth's orbit around the sun is given in kilometres)
 

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