. On this day in 1920 – April 26th – the Shapley-Curtis debate took place on the nature and distance of "spiral nebulae".
Even in 1920, we didn't know what the "spiral nebulae" were. Were they objects in our Milky Way galaxy and therefore comparatively close? Or were they "island universes", i.e., other galaxies, and therefore at a great distance?
We take forum safety very seriously here at BellaOnline. Please be sure to read through our Forum Guidelines. Let us know if you have any questions or comments!