Mike Stone's poem pictures the sun sliding down a mountainside as if it were something heavy and alive, a ball or a wave rolling downhill. The image is strange but easy to see: light spreading across a slope at the end of the day, or perhaps at its start. What stands out is that the trees don't change. They stay "where they stood," untouched by something so large passing by.
The speaker seems quietly puzzled by this. The line "as though light did not matter" sounds like a half-formed thought, a way of making sense of the stillness. Then the last line, "and yet it was true," turns it around. The speaker isn't sure what exactly is true, and the poem leaves that open. Maybe light does matter, or maybe the trees really are indifferent. The mood is calm but a little uneasy, like watching something enormous happen with no one reacting. The title, "Solar Storm," adds a hint of violence that the gentle scene never delivers.