Engineering Expert Witness Blog

      Astronomers tell us that the sun is approximately 93,000,000 miles from Earth.   Since no direct method of measuring this distance exists, how did scientists determine this?   They had to resort to indirect methods.

      In the early 18^th Century, British astronomer, mathematician and physicist Edmund Halley, of Halley’s Comet fame, devised a method to measure the distance between Earth and its sun with reasonable accuracy.   His method was based in part on an optical effect known as the principle of parallax, which had been discovered more than 2000 years ago by Greek astronomer Hipparchus when he also employed it to try and determine that same distance.

      Halley also employed the ideas of 17^th Century German mathematician, astronomer, and astrologist Johannes Kepler.   Kepler’s work on planetary motion, in particular the geometry of planetary orbits in our solar system, were vital to Halley’s distance measuring method.

      Next time we’ll see how Kepler’s Third Law of Planetary Motion brought Halley one step closer to methodology that would determine the distance of our home planet to its sun.

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