“Then will appear the sign of the Son of Man in heaven. And then all the peoples of the earth will mourn when they see the Son of Man coming on the clouds of heaven, with power and great glory"
(Matthew 24:30)
"in heaven" == in outer space.
The apparition of the "sign of the Son of Man" (==celestial cross) was historicized by the Passion Story. So what remains on the mouth of Jesus is the rest of the prophecy:
... the Son of Man coming on the clouds of heaven, with power and great glory