These two sections need to be read together, and—just as clearly—what we have in the closing sentences of Luke 24 is a summary of the information provided (with more detail) in Acts 1.
Interestingly, nowhere else in the NT do we find such an explicit description of the ascension/exaltation scene from the Easter tradition. The idea that Jesus was raised to glory with God, including variants that simply describe Jesus as being with the Father, is widely-attested in the NT. But no other NT writer attempts to describe the moment of glorification/exaltation.
Turning a metaphor into a physical reality is a classic Lukan characteristic, but the desire to provide a witness statement attesting to the ascension (and deification) of Jesus may reflect Luke's context in second century Roman society. Such statements were an essential part of the process for the Senate's confirmation of the apotheosis of a recently-deceased emperor.
See further discussion at Ascension