One of the most distinguishing phrases commonly used in “day of the Lord” imagery makes use of what we call “cosmic decreation” language. Cosmic decreation or deconstruction is exactly what it sounds like; the universe itself is unraveling—or at least, your little slice of it. Per Joel 2:31: “The sun shall be turned to darkness, and the moon to blood, before the great and awesome day of the Lord comes.” In Joel 3:15: “The sun and the moon are darkened, and the stars withdraw their shining.”
But there are many examples of “day of the Lord” language in the Old Testament.
Full transcript and small group discussion questions can be found at https://prophecycourse.org/session/more/day-of-the-lord/