That day
points to the eschatological future of the day of the Lord, previously pictured as a day of darkness and not light (Amos 5:18, Amos 5:20). This day is the great day of judgment when all people will stand before God, but it is also seen in smaller days of the Lord
when God intervenes in history to bring about judgment (e.g. the invasion of Assyria). In terms of darkness, two eclipses are calculated to have occurred in Amos’s lifetime, one in 784 BC and the other in 763 BC.1
9 “And on that day,” declares the Lord GOD, “I will make the sun go down at noon and darken the earth in broad daylight.