Immediately after the tribulation, etc. - Commentators generally understand this, and what follows, of the end of the world and Christ’s coming to judgment: but the word immediately shows that our Lord is not speaking of any distant event, but of something immediately consequent on calamities already predicted: and that must be the destruction of Jerusalem. “The Jewish heaven shall perish, and the sun and moon of its glory and happiness shall be darkened - brought to nothing. The sun is the religion of the Church; the moon is the government of the state; and the stars are the judges and doctors of both. Compare Isa 13:10; Eze 32:7, Eze 32:8, etc.” Lightfoot.
In the prophetic language, great commotions upon earth are often represented under the notion of commotions and changes in the heavens: -
The fall of Babylon is represented by the stars and constellations of heaven withdrawing their light, and the sun and moon being darkened. See Isa 13:9, Isa 13:10.
The destruction of Egypt, by the heaven being covered, the sun enveloped with a cloud, and the moon withholding her light. Eze 32:7, Eze 32:8.
The destruction of the Jews by Antiochus Epiphanes is represented by casting down some of the host of heaven, and the stars to the ground. See Dan 8:10.
And this very destruction of Jerusalem is represented by the Prophet Joel, Joe 2:30, Joe 2:31, by showing wonders in heaven and in earth - darkening the sun, and turning the moon into blood. This general mode of describing these judgments leaves no room to doubt the propriety of its application in the present case.
The falling of stars, i.e. those meteors which are called falling stars by the common people, was deemed an omen of evil times. The heathens have marked this: -
Saepe etiam stellas, vento impendente videbis
Praecipites coelo labi, noctisque per umbram
Flammarum longos a tergo albescere tractus
Virg. Geor. i. ver. 365
And oft before tempestuous winds arise
The seeming stars fall headlong from the skies,
And, shooting through the darkness, gild the night
With sweeping glories, and long trails of light
Dryden
Again the same poet thus sings: -
Sol tibi signa dabit: solem quis dicere falsum Audeat?