Two short images sit side by side here, and the poem leaves us to work out how they connect. The first is an owl hunting in daylight, which is unusual, since we expect owls at night. The second is "an apple sun for a horse," a picture of the sun as something round, bright, and edible, like a treat held out to an animal.
The title, "Sunstruck," ties them together. Both creatures seem caught off guard by the light, or perhaps transformed by it. The owl is out of its usual hours, while the horse is offered the sun as if the whole sky were a piece of fruit. The speaker doesn't tell us how they feel outright, but the tone suggests quiet wonder and a touch of playfulness. They seem to be watching closely and delighting in the odd, fresh way the world can look.
The mood is calm, bright, and a little surprising, like a moment you notice and then just want to stay inside.