What is Walt Whitman saying in his poem, When I Heard the Learn'd Astronomer? Is the learn'd astronomer supposed to be intelligent and brilliant?

Whitman seeks to expand the appreciation of both scientific phenomena and the natural world in this particular poem.  Representing a sense of American Romanticism, Whitman appreciates to a certain extent the astronomer's explanations (The title does not seem to be a sardonic reference of the astronomer's knowledge.)  Whitman does possess an appreciation for "the proofs" and "the figures," and does hold a certain respect for "the diagrams" and "the charts" along with the processes that account for them.  Where Whitman holds some level of divergence with this rationalist approach to the scientific phenomena is that Whitman feels there is a sense of wonderment and amazement that is not fully recognizable through the scientific method.  When Whitman describes his leaving the lecture hall as "riding" and "gliding off," it marks an active break with the established normative process of science and begins an embracing of the imaginative aspects of astronomy, and science in general. This is heightened with the use of the verb "wandering," indicating a certain heavenly and unexplained quality to the phenomena of stars and their alignment in the sky.  The "perfect silence" and image of the night sky lends an air of reverence which is not necessarily evident in the objective approach of the "learn'd astronomer"  and his applauding audience.  It seems that Whitman is embracing a form of negative capability in the picture he sees in the last line.  This idea of being comfortable with the unknown is something which is not amplified through the scientific approach, in its very nature seeking to quantify and explain.  Whitman is pointed in suggesting that while Science and rational thought does have a place in re-describing the natural world, there is a level of individual amazement and wonderment which will and should never be supplanted with rational thought.  This level or sphere which signifies the expansion of moral and individual imagination is intrinsic to the individual, the reason why he leaves the lecture hall when the group applauds the astronomer.