Many Americans will be treated to a rare total solar eclipse on August 21, when the shadow of the moon crosses in front of the sun in a path from Oregon to South Carolina. The eclipse, which will occur in the late morning on the West Coast, is expected to produce a 70-mile-wide band of darkness that will be seen by tens of millions of people. The same event happened back in 1878, and it was an important occurrence for three scientists who wanted to learn more. Journalist David Baron chronicles that story in his book, American Eclipse: A Nation’s Epic Race to Catch the Shadow of the Moon and Win the Glory of the World . Baron visited the Knowledge at Wharton show on  SiriusXM channel 111 to shed some light on those notable scientists. An edited transcript of the conversation follows. Knowledge at Wharton: You profiled Thomas Edison, James Craig Watson, who was a planet hunter, and astronomer Maria Mitchell. Why these three?…