The painting divides neatly down the middle. On the left side we have books and globes, then considered key repositories of knowledge. And on the right is the world of thought and reflection represented by the sitter, who adopts the classic thinker's pose: hand on chin, eyes apparently unfocused, looking slightly upwards into the middle distance.
The original title of the painting isn't recorded, but it is known as An Astronomer because the nearer of the two globes shows a celestial map of the stars and their constellations. Some art historians have suggested that it may be a self portrait, but the sitter does not resemble other images believed to be of Bol. More likely, it is an idealised depiction of an astronomer as a scientist and thinker - there are plenty of other examples in Dutch art around this time.
Credit: Presented by Miss E.A. Bennett, 1862