Luke 21:11
And great earthquakes will happen, and at various places there will be famines and disease epidemics. And there will be fearful events and great [supernatural] signs from heaven.
Matthew 24:29-30
"But immediately after the terrible trouble of those days, [i.e., the next major event on God's calendar], the sun will become dark, and [therefore] the moon will not [be able to] shed its [reflected] light. The stars will fall from the sky and the forces of the heavens will be shaken [Note: From the description of these same events in Luke 21:25-26, it is possible that this is figurative language for great calamities happening on the earth].
Luke 21:25-27
"Then [Note: This event answers to the "immediately" of Matt. 24:29, and suggests the next major event on God's calendar] there will be [supernatural] signs [evident] in the sun and moon and stars. And on earth [there will be] distress among nations; they will be perplexed by the roaring of the ocean's churning waves. [Note: Probably this is figurative language for highly agitated conditions on earth].