I will stick with what Peter said, since he was inspired by the Holy Spirit. The prophecy that he was quoting was from Joel 2, and it was being fulfilled at that time.
Did this happen at Pentecost?
==> Act 2:19 And I will shew wonders in heaven above, and signs in the earth beneath; BLOOD, and FIRE, and vapour of smoke:
==> Act 2:20 The SUN shall be turned into DARKENESS, and the MOON into BLOOD, before that GREAT and notable day of the Lord come:
Joel 2:28 And it shall come to pass afterward, [that] I will pour out my spirit upon all flesh; and your sons and your daughters shall prophesy, your old men shall dream dreams, your young men shall see visions:
Joe 2:29 And also upon the servants and upon the handmaids in those days will I pour out my spirit.
Joe 2:30 And I will shew wonders in the heavens and in the earth, blood, and fire, and pillars of smoke.
Joe 2:31 The sun shall be turned into darkness, and the moon into blood, before the great and the terrible day of the LORD come.
Joe 2:32 And it shall come to pass, [that] whosoever shall call on the name of the LORD shall be delivered: for in mount Zion and in Jerusalem shall be deliverance, as the LORD hath said, and in the remnant whom the LORD shall call.
Joel - Chapter 3
Joe 3:1 For, behold, in those days, and in that time, when I shall bring again the captivity of Judah and Jerusalem,
Joe 3:2 I will also gather all nations, and will bring them down into the valley of Jehoshaphat, and will plead with them there for my people and [for] my heritage Israel, whom they have scattered among the nations, and parted my land.
Joe 3:3 And they have cast lots for my people; and have given a boy for an harlot, and sold a girl for wine, that they might drink.
Joe 3:4 Yea, and what have ye to do with me, O Tyre, and Zidon, and all the coasts of Palestine? will ye render me a recompence? and if ye recompense me, swiftly [and] speedily will I return your recompence upon your own head;
Joe 3:5 Because ye have taken my silver and my gold, and have carried into your temples my goodly pleasant things:
Joe 3:9 Proclaim ye this among the Gentiles; Prepare war, wake up the mighty men, let all the men of war draw near; let them come up:
Joe 3:10 Beat your plowshares into swords, and your pruninghooks into spears: let the weak say, I [am] strong.
Joe 3:11 Assemble yourselves, and come, all ye heathen, and gather yourselves together round about: thither cause thy mighty ones to come down, O LORD.
Joe 3:12 Let the heathen be wakened, and come up to the valley of Jehoshaphat: for there will I sit to judge all the heathen round about.
Joe 3:13 Put ye in the sickle, for the harvest is ripe: come, get you down; for the press is full, the fats overflow; for their wickedness [is] great.
Joe 3:14 Multitudes, multitudes in the valley of decision: for the day of the LORD [is] near in the valley of decision.
Joe 3:15 The sun and the moon shall be darkened, and the stars shall withdraw their shining.
Joe 3:16 The LORD also shall roar out of Zion, and utter his voice from Jerusalem; and the heavens and the earth shall shake: but the LORD [will be] the hope of his people, and the strength of the children of Israel.
Joe 3:17 So shall ye know that I [am] the LORD your God dwelling in Zion, my holy mountain: then shall Jerusalem be holy, and there shall no strangers pass through her any more.
Joe 3:18 And it shall come to pass in that day, [that] the mountains shall drop down new wine, and the hills shall flow with milk, and all the rivers of Judah shall flow with waters, and a fountain shall come forth of the house of the LORD, and shall water the valley of Shittim.
Joe 3:19 Egypt shall be a desolation, and Edom shall be a desolate wilderness, for the violence [against] the children of Judah, because they have shed innocent blood in their land.
Joe 3:20 But Judah shall dwell for ever, and Jerusalem from generation to generation.
Joe 3:21 For I will cleanse their blood [that] I have not cleansed: for the LORD dwelleth in Zion.