{"knowledge_schema": {"broad_category": "Astronomy \u2192 Cosmology \u2192 Redshift and Spectroscopy", "refinement": "This problem involves understanding the redshift phenomenon, particularly how it affects the detection of light from distant astronomical objects through absorption lines.", "specific_scope": "The focus is on estimating the minimum redshift at which neutral hydrogen clouds can absorb light from quasars at the Lyman alpha wavelength, making them detectable with optical telescopes.", "goal": "Determine the lower limit of redshift for neutral hydrogen clouds to be observable through their absorption of light from background quasars."}, "summary": "This problem pertains to the field of astronomy, specifically the study of redshift and its implications for observing distant objects in the universe. It requires estimating the minimum redshift at which large clouds of neutral hydrogen can absorb light from quasars at the Lyman alpha wavelength (1216 Angstrom), allowing for their detection with optical telescopes. The goal is to find the lowest redshift value that meets this criterion, with the answer being 1.9."}