A long-standing astronomical mystery is “What type of star system will explode as a supernova?” It turns out that this question can be resolved by looking at century-old photographs. On studying archival data back to 1890, the result is that recurrent novae are the precursors to supernovae. With this knowledge, astronomical theorists can now perform the calculations to make subtle corrections that allow for the promise of precision-cosmology by upcoming programs involving supernovae. The lesson here is that old astronomical archives are valuable resources that can be used to produce unique and front-line science, in ways that no combination of modern telescopes can provide. [More]