Focusing ethnographically on astronomers engaged in “look back studies” of cosmic evolution, this essay considers how they make telescopic observations at an optical observatory in the context of their epistemic work at other sites. Foucault’s notion of a heterotopia captures key aspects of how the observatory is set apart from astronomers’ work with digital data elsewhere. However, visual practices of interpreting telescopic exposures in the observatory’s control room do reach across this divide and inform later epistemic work, such as when scientists use these exposures retrospectively as windows into the functioning of telescopes and detectors. Visiting astronomers remark that witnessing the emergence of exposures in the control room asserts to them the reality of the cosmic objects they study. I interpret this as being grounded in their understanding of semiosis.