There is one crucial detail Hillary Clinton hasn’t divulged to the American people, and it’s driving Michael O’Reilly bonkers.

Mr. O’Reilly of Bend, Ore., is an astrologer. He knows Donald Trump was born at 10:54 a.m. in Jamaica Hospital in Queens on June 14, 1946. From that, it’s possible to divine that the GOP candidate “has a very strong Mars vibe going on,” he says.

The red planet’s position in Mr. Trump’s natal chart—the precise layout of the heavens at the moment of birth—resonates with Americans fed up with Washington, says Mr. O’Reilly. Mars exudes the Roman war god’s temperament, and Mr. Trump is “basically channeling that energy.”

Mrs. Clinton was born Oct. 26, 1947, at Edgewater Hospital in Chicago, Ill., according to the Cook County Clerk. After that, astrologers must play gumshoe to get any closer. There’s decent historical evidence for two times at either end of the day. The Clinton campaign declined to answer questions, ensuring the mystery will continue.

“The craft of forecasting is really impossible unless we have a birth time,” says Mr. O’Reilly. “But the public demands it.”