What specific analytical method, applied in the 19th century, provided concrete evidence that starlight's chemical signature resembled sunlight?

Answer

Spectroscopy

Angelo Secchi used spectroscopy in the 19th century to analyze starlight, finding its chemical signature to be strikingly similar to that of sunlight, thus confirming their shared nature.

What specific analytical method, applied in the 19th century, provided concrete evidence that starlight's chemical signature resembled sunlight?
sunastronomystarcelestial body