In Orthodox Christianity, The Feast of the Ascension of our Lord God and Savior Jesus Christ is celebrated each year on the fortieth day after The Great and Holy Feast of Pascha (Easter). Since the date of Pascha changes each year, the date of the Feast of the Ascension changes. The Feast is always celebrated on a Thursday. This year, today, May the 28th is said Thursday.
The Feast itself commemorates when, on the fortieth day after His Resurrection, Jesus led His disciples to the Mount of Olives, and after blessing them and asking them to wait for the fulfillment of the promise of the Holy Spirit, He ascended into heaven.
The Lord Jesus passed forty days on earth after His Resurrection from the dead, appearing continually in various places to His disciples, with whom He also spoke, ate, and drank, thereby further demonstrating His Resurrection. On this Thursday, the fortieth day after Pascha, He appeared again in Jerusalem. After He had first spoken to the disciples about many things, He gave them His last commandment, that is, that they go forth and proclaim His Name to all nations, beginning from Jerusalem. But He also commanded them that for the present, they were not to depart from Jerusalem, but to wait there together until they receive power from on high, when the Holy Spirit would come upon them.
https://www.goarch.org/chapel/saints?contentid=943&PCode=6PTh&D=T&date=05/28/2020
Saying these things, He led them to the Mount of Olives, and raising His hands, He blessed them; and saying again the words of the Father’s blessing, He was parted from them and taken up. Immediately a cloud of light, a proof of His majesty, received Him. Sitting thereon as though on a royal chariot, He was taken up into Heaven, and after a short time was concealed from the sight of the disciples, who remained where they were with their eyes fixed on Him. At this point, two Angels in the form of men in white raiment appeared to them and said, “Ye men of Galilee, why stand ye gazing up into Heaven? This same Jesus, Who is taken up from you into Heaven, shall so come in like manner as ye have seen Him go into Heaven” (Acts 1:11). These words, in a complete and concise manner, declare what is taught in the Symbol of Faith concerning the Son and Word of God. Therefore, having so fulfilled all His dispensation for us, our Lord Jesus Christ ascended in glory into Heaven, and sat at the right hand of God the Father. As for His sacred disciples, they returned from the Mount of Olives to Jerusalem, rejoicing because Christ had promised to send them the Holy Spirit.
Christ has ascended! Truly He has ascended!
http://www.pravmir.com/the-ascension-a-beginning-not-an-ending/