Answer:
There could be several reasons but having seen the poem would provide a clearer answer.
Explanation:
They could use this phrase as an attempt of creating a concise understanding that the astronomer was qualified or learn'd from. It could be a use of imager or even personification. If the poem was posted, I would be able to answer it better.
In the short story "The Lottery," the lottery is drawn from a black box.
They used many boxes prior to the lottery in the story, but they were shabby and got destroyed, so they got a new box which was black of color.
