In Acts 2 when Peter stood up and addressed the crowd he repeated what prophet Joel said concerning the last days and two of these scriptures were:
 
19 I will show wonders in the heavens above
and signs on the earth below,
blood and fire and billows of smoke.
20 The sun will be turned to darkness
and the moon to blood
before the coming of the great and glorious day of the Lord.
 
The timing for these events I see at the sixth seal in Revelations.
 
12 I watched as he opened the sixth seal. There was a great earthquake. The sun turned black like sackcloth made of goat hair, the whole moon turned blood red, 13 and the stars in the sky fell to earth, as figs drop from a fig tree when shaken by a strong wind. 14 The heavens receded like a scroll being rolled up, and every mountain and island was removed from its place.
 
Now it is quite curious Peter changed the understanding of the Day of the Lord to Great and Glorius instead of Great and Terrible/Dreadful Day of the Lord. In Old Testament nothing glorius is said about the Day of the Lord, always about judgement and destruction.  Peter was looking forward to the Day of the Lord.  And in 2 Thess 2 the Day of the Lord cannot come till the antichrist takes his seat in temple of God.
 
I would also like to note on this Pentecost approx. 3000 souls were saved.  Reminds me of when Israel lost approx. 3000 souls for making the idol when the Law was given on that first Pentecost. God is a great book keeper!