Grant Mathews, professor of theoretical astrophysics and cosmology in the University of Notre Dame’s College of Science, believes the event that led the Magi — Zoroastrian priests of ancient Babylon and Mesopotamia — was a rare planetary alignment occurring in 6 BC. The Journey of the Three Kings by Leopold Kupelwieser, 1825. “Astronomers, historians and theologians have pondered the question of the ‘Christmas Star’ for many years,”...