What is one thing that the poet challenges in the poem, Witness?

This poem challenges the notion that science and art are mutually exclusive. The close observation of the night sky, the study of astronomy, can be transformed into poetry. A comet can be understood in terms of a metaphor. The physics involved in understanding how a comet orbits the Sun can morph into images of “the foothills of a green century.” The concept of time provides the poet with an idea of how “terrestrial hands” (literal and metaphoric) allow one to read “the heaven clock.” Humans tell time by the location of stars; geologists estimate the Earth’s age by the location of tectonic plates, by theorizing about the movement of continents. All of this science is material for a poet to use in shaping a poem.