There are two seemingly contradictory aspects to Christ's prophecy that we need to harmonize. On the one hand, Jesus spoke of cataclysmic events immediately following the tribulation, when the heavenly luminaries go into eclipse; and on the other hand he spoke of the tribulation being cut short for the sake of the chosen ones. The question is how do we harmonize these? For example, what did Jesus mean when he said that the great tribulation will be cut short? Would it be cut short because Armageddon would intervene? That is not reasonable.  In order to shed light upon Jesus' enigmatic prophecy, it is necessary to examine other related prophecies.

You cited Joel 2:10-11, so that is a good place to start. Those two verses read: "Into the city they rush. On the wall they run. On the houses they go up. Through the windows they go in like the thief. Before it the land has become agitated, the heavens have rocked. Sun and moon themselves have become dark, and the very stars have withdrawn their brightness. And Jehovah himself will certainly give forth his voice before his military force, for his camp is very numerous. For he who is carrying out his word is mighty; for the day of Jehovah is great and very fear-inspiring, and who can hold up under it?"

As noted, Joel uses the same apocalyptic language as Christ did when discussing the events immediately after the tribulation. But is Joel 2:10-11 describing Armageddon? No. The great and fear-inspiring day of Jehovah in that prophecy, during which time the heavens rock and the symbolic sun, moon, and stars go on the wane, is connected to an onrushing locust-like army of invaders. Jehovah's "military force," as it is called, is not the standing army of heavenly angels, such as will be deployed during the actual war of Armageddon. No, Jehovah's great and fear-inspiring military force is the earthly agency that God uses to execute his judgments upon his people and the world.

The 13th chapter of Isaiah is a parallel prophecy to Joel. In Isaiah, Jehovah refers to the army of his executionary forces as "my sanctified ones."  "I myself have issued the command to my sanctified ones. I have also called my mighty ones for expressing my anger, my eminently exultant ones. Listen! A crowd in the mountains, something like a numerous people! Listen! The uproar of kingdoms, of nations gathered together! Jehovah of armies is mustering the army of war. They are coming from the land far away, from the extremity of the heavens, Jehovah and the weapons of his denunciation, to wreck all the earth."

What does it mean that Jehovah's army is going "to wreck all the earth"? It means that the established order of things is going to be violently overturned. It means that long-standing, stable institutions are suddenly overthrown and shattered. Isaiah goes on, saying: "Howl, you people, for the day of Jehovah is near! As a despoiling from the Almighty it will come. That is why all hands themselves will drop down, and the whole heart itself of mortal man will melt. And people have become disturbed. Convulsions and birth pains themselves grab hold; like a woman that is giving birth they have labor pains. They look at each other in amazement. Their faces are inflamed faces. Look! The day of Jehovah itself is coming, cruel both with fury and with burning anger, in order to make the land an object of astonishment, and that it may annihilate the land's sinners out of it. For the very stars of the heavens and their constellations of Kesil will not flash forth their light; the sun will actually grow dark at its going forth, and the moon itself will not cause its light to shine."

As in Joel, please take note of the fact that the day of Jehovah's onrushing military force also results in the heavenly luminaries being snuffed out.

Consider another related prophecy: Ezekiel chapters 29-32 foretell the downfall of the ancient Egyptian empire. However, the prophecy aptly foreshadows the United States of America. (See Doom of the Anglo-American Dyad.)  "And when you get extinguished I will cover the heavens and darken their stars. As for the sun, with clouds I shall cover it, and the moon itself will not let its light shine. All the luminaries of light in the heavens—I shall darken them on your account, and I will put darkness upon your land,' is the utterance of the Sovereign Lord Jehovah. And I will offend the heart of many peoples when I bring the captives from you among the nations to lands that you have not known. And at you I shall certainly cause many peoples to be awestruck, and their kings themselves will shudder in horror at you when I brandish my sword in their faces, and they will have to tremble every moment, each one for his own soul, on the day of your downfall."

Interestingly, Ezekiel 30:3 says that Jehovah's Day of Judgment upon Egypt is "a day of clouds, an appointed time of nations it will prove to be." Whereas Joel and Isaiah describe Jehovah's military force crushing the world, in this particular prophecy in Ezekiel Jehovah pinpoints the downfall of a specific kingdom, namely the anti-typical Egyptian power, as initiating a time of world-wide terror upon all of earth's kingdoms.

So, the commonality of the three prophecies that we have briefly considered is that Jehovah's Day of Judgment commences with the overthrow of established kingdoms; which ushers in a dark age of doom and foreboding—represented universally in the Scriptures by symbolism denoting the heavenly luminaries becoming darkened. Obviously, these prophecies parallel what Jesus foretold concerning men becoming faint out of fear due to the powers of the heavens being shaken. Also, the fall of Egypt into the hands of a tyrant undoubtedly compliments the 13th chapter of Revelation concerning the beast that received the deadly sword-stroke to one of its seven heads.

Finally, consider more closely what exactly does and does not occur with the opening of the 6th seal. After describing the sun becoming black as sackcloth and the moon turning blood-red; and the stars of heaven falling from the sky, Revelation 6:15-17 says: "And the kings of the earth and the top-ranking ones and the military commanders and the rich and the strong ones and every slave and every free person hid themselves in the caves and in the rock-masses of the mountains. And they keep saying to the mountains and to the rock-masses: "Fall over us and hide us from the face of the One seated on the throne and from the wrath of the Lamb, because the great day of their wrath has come, and who is able to stand?"

It is evident that the opening of the 6th seal does not immediately result in Armageddon. How do we know that? Because the cataclysmic collapse of the system is not the end of the world. The fact that men seek refuge in the "caves" and "rock masses" is indicative that there is an interim period, a cutting short of the tribulation if you will, when men seek to perpetuate the system that has come under the heat of God's anger; by looking to alternative institutions for protection and salvation. That is, in fact, what Judgment Day is all about. It is a period of extreme distress when all of mankind is forced to decide whom they will look to for salvation. The two choices being: The kingdom of Christ or the revived beast in the form of the 8th king.  That is when men become permanently tattooed with the symbolic 666 mark of the beast if they do not give their full allegiance to Christ's kingdom. So, it stands to reason that there would have to be an interval after the system crashes, after the tribulation, when Satan puts forward his counterfeit savior, until Jehovah finally annihilates the beast altogether.

Something else to keep in mind is that the main feature of the great tribulation is that the political disgusting thing desolates God's holy place. If the disgusting thing represents the 8th king after his revival from his near-death experience, then that means that the 7th king will have already given way to the 8th king before that phase of the tribulation is reached. So, as we have seen by a comparison of several Hebrew prophecies, the symbolic heavenly luminaries must come down before the great tribulation reaches its climax.

Ultimately, though, Jehovah's judgments will not become entirely clear until we actually enter into the conclusion of the system.