On these plates, I would think stars effectively are point light sources (https://en.wikipedia.org/wiki/Point_source#Visible_electromagnetic_radiation_(light) h

On these plates, I would think stars effectively are point light sources (https://en.wikipedia.org/wiki/Point_source#Visible_electromagnetic_radiation_(light) https://en.wikipedia.org/wiki/Point_source#Visible_electroma...) If so, there’s not much more to see on these plates than position and brightness (I assume these were black and white plates, as color photography still was fairly experimental in 1870) Also they didn’t make the map to look at individual stars (they wouldn’t use “pictures of an enormous 3x2 degrees of the sky” for that), but to answer questions such as whether the distribution of stars is uniform or whether stars move relatively to each other in the sky. For both, you need positions.