A mini monolith to the idea that the only thing that deserves worship is the sun. Although this may have been the seed for many religions, over time, the Christian ‘story’ became the default position for western European societies and beyond. (eg. What year is it?)
So, much like Athelstan (in the Amazon series Vikings, who worships his god in secret, out of sight of the dominant religion at large) this modest, behind closed doors, sundial-like object represents atheism, but appropriates a romanticised ritual gesture of religion to do so.