What event marks the end of Luke's Gospel and the beginning of Acts?

Luke's Gospel and Acts of the Apostles were written by the same author, long assumed to be the apostle Luke. The Gospel was written first, with Acts apparently written after an interval, during which some of Luke's assumptions may have changed.

Luke's Gospel ends when the risen Jesus last spoke to the disciples and was then taken bodily up into heaven on the evening of the day of his resurrection.

Acts begins when the risen Jesus, who had remained on earth for forty days, seen by many, last spoke to the disciples and was then taken bodily up into heaven.