Whitman frequently views man as being a part of nature in his writings, but not in "When I Heard the Learn'd Astronomer." The world of culture and knowledge – the ivory tower – stands apart from nature and even obscures it. With all of our equations and formulas, we think that we are learning about objects in nature when in fact we are just playing around in a closed and confined internal world. Knowledge of nature can only come from experience, he argues. It transmits itself to a willing soul as if by osmosis. Only the sensitive individual can integrate himself with his natural surroundings. If you like this philosophy, you might want to read Henry David Thoreau's classic book, Walden, written during the same period in American history.
The poem describes the modern condition of humanity: we cannot feel at home in the world because we have too much knowledge of it.