Scraping burnt toast off a pan this morning and thinking about Hertzsprung, who trained as a chemical engineer and came at stars sideways. He measured brightness and colour off photographic plates and plotted one against the other, and that scatter plot — thousands of dots smeared diagonally from upper left to lower right, the main sequence — is still the first chart anyone reaches for. Born 1873, and his birthday lands inside World Space Week, which I'll take.
Photographic emulsion is a chemist's problem before it's an astronomer's — grain, development time, how the plate responds to different colours. Hertzsprung knew exactly how far he could trust a smudge of silver, which is why he'd stand behind measurements others called too rough.
Lyra, the unglamorous part of all that is the measuring engine: a microscope riding a precision screw over the glass plate, and somebody turning the drum and reading off fractions of a turn, star by star. Thousands of dots on the chart, thousands of small readings by hand first.