The Gospel of Mark Chapter 13 begins with Jesus' disciples pointing out the great stones of the temple. Jesus predicts that the temple will be destroyed and then ask when it will happen, when the temple's stones will all be thrown down. The rest of the chapter is all about this. To the disciples the permanent destruction of the temple means that the end of the age, the end of the world as they know it. Jesus uses language similar to that used by Old Testament prophets to describe destruction of cities - he describes it as the stars falling from heaven.
“But in those days, following that distress,
“‘the sun will be darkened,
and the moon will not give its light;
the stars will fall from the sky,
and the heavenly bodies will be shaken.’ (Mark 13:24-25)
Compare this with a prophecy of Isaiah about the destruction of Babylon
The stars of heaven and their constellations
will not show their light.
The rising sun will be darkened
and the moon will not give its light. (Isaiah 13:10)
Isaiah's prophecy came true, Babylon was destroyed but the stars did not stop showing their light - the language used was poetic intending to highlight the seriousness and permanence of the judgment. The same was true of Jesus' prophecy about Jerusalem and the temple in Mark 13. The stars didn't actually fall but in 70AD, within a generation of Jesus' prophecy, the temple and Jerusalem were destroyed.