Revelation 6:12-17 NKJV

12 I looked when He opened the sixth seal, and [g]behold, there was a great earthquake; and the sun became black as sackcloth of hair, and the [h]moon became like blood. 13 And the stars of heaven fell to the earth, as a fig tree drops its late figs when it is shaken by a mighty wind. 14 Then the sky [i]receded as a scroll when it is rolled up, and every mountain and island was moved out of its place. 15 And the kings of the earth, the great men, [j]the rich men, the commanders, the mighty men, every slave and every free man, hid themselves in the caves and in the rocks of the mountains, 16 and said to the mountains and rocks, “Fall on us and hide us from the face of Him who sits on the throne and from the wrath of the Lamb! 17 For the great day of His wrath has come, and who is able to stand?”

Notice that the cosmic signs described in verses 12–14 occur when the sixth seal is opened. Then, after witnessing these events, the inhabitants of the earth cry out, "For the great day of His wrath has come" (v.17). Their own testimony identifies this moment as the beginning of the Day of the Lord. Has this day happened yet? As of this writing, no, but we know from scripture when this day will happen. No, we don’t have a specific date, but we have clues that occur just before this day that we as believers need to watch and pray about.

Here are scriptures that tells us the signs we will see when this day takes place.

Joel 2:30-31 NKJV

30 “And I will show wonders in the heavens and in the earth: Blood and fire and pillars of smoke. 31 The sun shall be turned into darkness, And the moon into blood, Before the coming of the great and awesome day of the Lord.

Joel describes the same heavenly signs that John records in Revelation—the sun darkened and the moon turned to blood. Joel adds an important detail: these signs occur before the coming of the Day of the Lord. When these same signs appear in Revelation 6, the inhabitants of the earth immediately recognize that God's day of wrath has arrived. Scripture is confirming Scripture.

Matthew 24:29-31 NKJV

29 “Immediately after the tribulation of those days the sun will be darkened, and the moon will not give its light; the stars will fall from heaven, and the powers of the heavens will be shaken. 30 Then the sign of the Son of Man will appear in heaven, and then all the tribes of the earth will mourn, and they will see the Son of Man coming on the clouds of heaven with power and great glory. 31 And He will send His angels with a great sound of a trumpet, and they will gather together His [d]elect from the four winds, from one end of heaven to the other.

Jesus describes the same sequence of heavenly signs—the sun darkened, the moon affected, the stars falling, and the heavens shaken. These parallels strongly connect His teaching with the events surrounding the sixth seal. Later, in Revelation 7, John records the sealing of the 144,000 followed by the appearance of a great multitude in heaven before God's throne. Taken together, these passages present a consistent prophetic picture. He’s telling everyone (this is the audience He’s speaking to: Israel, The Church, and the unbelievers), look at these signs. Scripture confirming scripture.

Isaiah 13:6-10 NKJV

6 Wail, for the day of the Lord is at hand! It will come as destruction from the Almighty. 7 Therefore all hands will be limp, Every man’s heart will melt, 8 And they will be afraid. Pangs[d] and sorrows will take hold of them; They will be in pain as a woman in childbirth; They will be amazed at one another; Their faces will be like flames. 9 Behold, the day of the Lord comes, Cruel, with both wrath and fierce anger, To lay the land desolate; And He will destroy its sinners from it. 10 For the stars of heaven and their constellations Will not give their light; The sun will be darkened in its going forth, And the moon will not cause its light to shine.

Isaiah adds another witness by connecting the Day of the Lord with God's wrath, the darkening of the sun, and the dimming of the moon. Once again, the prophets describe the same heavenly signs surrounding that day.

Isaiah 2:17-22 NKJV

17 The [d]loftiness of man shall be bowed down, And the haughtiness of men shall be brought low; The Lord alone will be exalted in that day, 18 But the idols [e]He shall utterly abolish. 19 They shall go into the holes of the rocks, And into the caves of the [f]earth, From the terror of the Lord And the glory of His majesty, When He arises to shake the earth mightily. 20 In that day a man will cast away his idols of silver And his idols of gold, Which they made, each for himself to worship, To the moles and bats, 21 To go into the clefts of the rocks, And into the crags of the rugged rocks, From the terror of the Lord And the glory of His majesty, When He arises to shake the earth mightily. 22 Sever[g] yourselves from such a man, Whose breath is in his nostrils; For [h]of what account is he?

Isaiah even records mankind fleeing into the caves and rocks because of the terror of the Lord when He shakes the earth. John's description in Revelation 6 is remarkably similar, suggesting that both prophets are describing the same event from different points in history.

1 Thessalonians 5:2-4 NKJV

2 For you yourselves know perfectly that the day of the Lord so comes as a thief in the night. 3 For when they say, “Peace and safety!” then sudden destruction comes upon them, as labor pains upon a pregnant woman. And they shall not escape. 4 But you, brethren, are not in darkness, so that this Day should overtake you as a thief.

2 Peter 3:10 NKJV

10 But the day of the Lord will come as a thief in the night, in which the heavens will pass away with a great noise, and the elements will melt with fervent heat; both the earth and the works that are in it will be [d]burned up.

Peter and Paul (through 1 Thessalonians) reminds believers that although the Day of the Lord will come unexpectedly upon the unbelieving world, it should not surprise those who are watching the signs God has already revealed through the prophets.

Summary of When the Day of the Lord takes place?
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The prophets consistently teach that immediately before the Day of the Lord the sun is darkened, the moon appears as blood, the heavens are shaken, and mankind witnesses extraordinary signs in heaven and on earth. Revelation records these same signs when the sixth seal is opened. It is at that moment that the inhabitants of the earth declare, 'For the great day of His wrath has come' (Revelation 6:17). By comparing Scripture with Scripture, the sixth seal consistently aligns as the biblical point at which the Day of the Lord begins.