When William Henry Harrison, the governor of Indiana Territory, heard of the Delaware witch purge of 1806 he sent the tribe a letter demanding that they denounce the Shawnee prophet as an "imposter." He did so with poetic language:
If he really is a prophet, ask of him to cause the sun to stand still - the moon to alter its course - the rivers to cease to flow - or the dead to arise from their graves. if he does these things, you may then believe he has been sent from God.The prophet, still known as Lalawethika at that time, claimed to receive revelations from the "Master of Life," his term for the Great Spirit. He answered Governor Harrison's challenge by predicting that the Master of Life would turn the sun black on June 16, 1806.
Incredibly, a solar eclipse really did occur that day. And, as one might imagine, it did something for the prophet's reputation. The Native confederacy that nowadays is usually identified with the prophet's brother, Tecumseh, owed a lot to Lalawethika/Tenskwatawa.
By predicting the eclipse did the Shawnee prophet prove that he was not an "imposter"?
Not necessarily. There were scientists around Lake Erie in 1806 positioning themselves for a good view of the eclipse. Some of them may have talked to the prophet or his followers. There were also white farmers in the area that kept almanacs with information about eclipses and other astronomical events. The prophet's brother,Tecumseh, could read English and may have come across an almanac.
Sources:
A speech of Governor Harrison to the Delawares "Early in 1806" as printed in Esarey, Logan (Editor) Messages and Letters of William Henry Harrison (vol.1, pages 182-184). New York: Arno Press, 1975. See this book on the Internet Archive.
Eclipse Chasers website: Tecumseh and the Eclipse of 1806
Cave, Alfred (2006) Prophets of the Great Spirit pages 87-88