Mark 13:24 But in those days, after that tribulation, the sun shall be darkened, and the moon shall not give her light,
This sounds like smoke, such as was in Kuwait during the Gulf war. Burning oil wells darkened the sun and the moon. There will be much fire. What is this tribulation and it's source? It is the judgment of God on the earths evil people. Self destruction, nation against nation and also the wrath of God poured out on Christ rejecting people. Their sins had caused them to worship the evil one. God will but an end to this evil, a cleansing before the return of Jesus Christ, the eternal king, with his saints.
Mark 13:25 And the stars of heaven shall fall, and the powers that are in heaven shall be shaken.
This could be literal stars, comets, and their effect on the earth...groaning in travail.
1 Th 5:3 For when they shall say, Peace and safety; then sudden destruction cometh upon them, as travail upon a woman with child; and they shall not escape.
1 Th 5:4 But ye, brethren, are not in darkness, that that day should overtake you as a thief.
1 Th 5:5 Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness.
Rom 8:22 For we know that the whole creation groaneth and travaileth in pain together until now.
Rom 8:23 And not only they, but ourselves also, which have the firstfruits of the Spirit, even we ourselves groan within ourselves, waiting for the adoption, to wit, the redemption of our body.
The powers that are in heaven, the sky above, shall be shaken, or the stars that are angels: Fallen angels gathered up for hell.
Mark 13:26 And then shall they see the Son of man coming in the clouds with great power and glory.
They who are on earth shall see the Lord descending in the clouds.
Mat 24:30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory.
Two responses from two kinds of people. The unredeemed, those who took on the mark of the Beast, shall mourn, for they soon shall be cast into hell. The elect, the people of God will rejoice at the Lord's coming. For he will be returning as the word of God said he would.
Acts 1:8 But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.
Acts 1:9 And when he had spoken these things, while they beheld, he was taken up; and a cloud received him out of their sight.
Acts 1:10 And while they looked stedfastly toward heaven as he went up, behold, two men stood by them in white apparel;
Acts 1:11 Which also said, Ye men of Galilee, why stand ye gazing up into heaven? this same Jesus, which is taken up from you into heaven, shall so come in like manner as ye have seen him go into heaven.
Mark 13:27 And then shall he send his angels, and shall gather together his elect from the four winds, from the uttermost part of the earth to the uttermost part of heaven.
His angels shall gather the elect from the four winds, the four directions of the earth.
Rev 7:1 And after these things I saw four angels standing on the four corners of the earth, holding the four winds of the earth, that the wind should not blow on the earth, nor on the sea, nor on any tree.
From the uttermost part of heaven? Just a thought about this. Maybe men will be in the heavens? Already we have had men on the moon and on space stations. Wherever they may be, alive or dead in Christ, the angels shall gather them together unto Christ Jesus.
Another spiritual thought concerning Jesus returning in the clouds. Perhaps it refers to the cloud of witnesses, the saints in heaven who will return with him?
Heb 12:1 Wherefore seeing we also are compassed about with so great a cloud of witnesses, let us lay aside every weight, and the sin which doth so easily beset us, and let us run with patience the race that is set before us,
Heb 12:2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God.
There is also the cloud of glory, the presence of God in a cloud.
On the mount of transfiguration
Mat 17:5 While he yet spake, behold, a bright cloud overshadowed them: and behold a voice out of the cloud, which said, This is my beloved Son, in whom I am well pleased; hear ye him.
Before the judgment of the high priest
Mat 26:63 But Jesus held his peace. And the high priest answered and said unto him, I adjure thee by the living God, that thou tell us whether thou be the Christ, the Son of God.
Mat 26:64 Jesus saith unto him, Thou hast said: nevertheless I say unto you, Hereafter shall ye see the Son of man sitting on the right hand of power, and coming in the clouds of heaven.
The evidence is in. Without a doubt, Jesus is coming back in the clouds to be with his people. Some will miss out because of unbelief.
Mat 26:65 Then the high priest rent his clothes, saying, He hath spoken blasphemy; what further need have we of witnesses? behold, now ye have heard his blasphemy.
Mat 26:66 What think ye? They answered and said, He is guilty of death.
God is the final judge. It is down to one question: Who is Jesus to you? He is my Lord and my savior. I look forward to that day when we shall see him, as he returns in the cloud.