Does anyone know this story?

This has been driving me crazy. Ten or twelve years ago, I posted to rec.art.sf.written asking about this story and someone identified it. I can’t for the life of me remember the name or author, now that a decade has passed. I think it might have been a Poul Anderson story. I looked back through my email from 10 years ago and no trace can be found. Essentially the story can be best summarized as this:

The main character of the story is fascinated by a painting by someone (Da Vinci, I think). There’s something about the quality of light in the painting that stirs some memory within him. It turns out that the man had been on the moon before and realizes that the quality of light in the Da Vinci painting is exactly that quality of light that appears only on the moon–implying that Da Vinci had been on the moon somehow.

Does anyone know the title and author of this story? It would be a great relief to finally know. Thanks in advance.