This is the "Apollo slaying Coronis" by Domenichino. Painted in the Italian north, it's a powerful depiction of the Greek sun god Apollo tumbling from the sky to shoot his unfaithful lover, Coronis. This painting was originally one of ten frescoes adorning the walls of a room in a garden pavilion at the Villa Aldobrandini near Rome.
It's based on a story from Ovid's Metamorphoses and is part of a larger iconographical scheme designed by Giovanni Battista Agucchi to glorify the Aldobrandini family and express their philosophical and religious ideas. Apollo, as the god of reason, is triumphant over the forces of chaos.
You can see that the composition has been revised and adapted for canvas, with Domenichino's original design influenced by illustrations in printed editions of Ovid's work. Unfortunately, much of the actual painting was left to assistants due to Domenichino's busy schedule at the time. Still, this piece is a remarkable example of his skill and artistry.
Apollo slaying Coronis hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.