The Speed of Light and the Moons of Jupiter Introduction: In this lab we focused on the eclipses of the moon Io of Jupiter. Galileo was the first to discover the four moons of Jupiter and since then astronomers have discovered the orbital periods of them, 1. 8 days being approximately Io’s. It was also noted that these moons disappeared and reappeared at certain points in their orbit. This was because when the moons were behind Jupiter they were not able to reflect light. In this lab we had to find the speed of light after finding the eclipse of Io given the dates March 1, 2008 and May 31, 2008. Procedure:

Using the CLEA program, first we chose two dates, March 1, 2008 being the far date and May 31, 2009 being the near date. Then we observed the time when Io moves into Jupiter’s shadow on the far date by moving it in very small intervals until the simulation of Io disappeared. Then we estimated how many orbits Io will make from the far date to the near date by dividing 92 (the number of days in between) but 1. 769861 (Io’s orbital period). We found 51 orbits. Then using this number we multiplied it by Io’s orbital period to find the time interval from the first eclipse to the predicted eclipse on the near date and got 90. 62911. Then we predicted the Julian date of the near date by adding this number to the Julian day of the far date. Next we observed the eclipse of the near day by once again moving in small increments to get an accurate time of when Io disappeared. Once we got this we find the difference between the prediction of the actual eclipse and got . 009832. We also found the change in distance between Jupiter and Earth from the far and near date, which was listed on the program. Then we used this number of 1. 9618 x 1011 and divided it by difference in time, which converted into seconds, is 849. 4848 to find the speed of light. Conclusion: This number we found for the speed of light was 2. 3498713 x 108. This is pretty close actual number of 3 x 108 and is probably just off from rounding errors. I found this lab very interesting because there were a lot of different aspects that all tied to each other. I was surprised to find out that finding the times of Jupiter’s moon Io’s eclipses could end up in the calculation of the speed of light.