Published on Mar 28, 2020

The objective: My objective is to measure the distance to Jupiter in order to measure the speed of light.

I used parallax to find the distance to Jupiter at opposition, and then derived equations to calculate this distance at other times. I observed and recorded the times of numerous Io eclipses, and used these to find a time lag.

By coupling the distance changes and the time lag, I calculated the speed of light.

I used the telescope that I built as part of my project from last year, CalSky star maps and viewing predictions, a stopwatch, a clock, and recording materials (pen, paper, etc.).

Distance to Jupiter at opposition: 4.2 AU (4.4 AU actual)

Changes in Distance: 0.0486 AU (0.0482 AU actual)

Speed of Light: 383,000 km/sec (299,729 km/sec actual)

My parallax measurements yielded a result with about 5% error. However, errors in my estimated change of distance were smaller (about 1%). While these distances were fairly accurate, my overall speed of light estimate was very sensitive to small timing errors.

The result was too high, almost 30% faster than the accepted value, and could easily have been off by much more. My procedure presents a valid approach, but is not necessarily the most practical method; extreme accuracy in observations is required to get good results.

However, taking into consideration my homemade telescope and the needed precision, my project produced a surprisingly close estimate.

This project is about measuring the distance to Jupiter and timed Io's eclipses to estimate the speed of light.

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