Brain Snacks: Tasty Tidbits of Knowledge
Starting in the 1860s, some of Whitman's most enthusiastic readers began to regard him as a kind of religious prophet – a "mystical" personality. (Source)
In the year in which this poem was written, Whitman was fired from his job as a clerk in the Indian Bureau of the Department of the Interior, because the Secretary of the Interior had heard that Whitman's writings were "obscene." (Source)
One of the major scientific advances in astronomy in the 19th century was a process called "spectroscopy." It allowed astronomers to measure the light and radiation emitted from stars, planets, and other celestial bodies. Maybe some of the "learn'd astronomers" charts had to do with spectroscopy! (Source)