A.T. Robertson Commentary Mark 13:25

"and the stars shall be falling from heaven, and the powers that are in the heavens shall be shaken." — Mark 13:25 (ASV)

The stars shall be falling (ο αστερες εσοντα πιπτοντες). Periphrastic future indicative, εσοντα, future middle indicative and πιπτοντες, present active participle.