It was this photograph’s anniversary today, or so said Robert McNees, posting on Bluesky’s science-communication feed.
On the 29th of December, 1888, a Welsh businessman, engineer, and keen amateur astronomer named Isaac Roberts snapped this photograph of what he called “the Great Nebula of Andromeda.” In 1888, nobody knew what a “galaxy” was yet. It was some sort of spiral formation of gas and dust, right? That couldn’t be a spinning collection of stars an unfathomable distance away … could it?
By comparison, if it helps to enter the headspace of the man who took this photograph, in 1888, the countries of Italy and Germany were both less than 20 years old, and the first automobile (the Benz Patent-Motorwagen) had only been for sale for two years. American women would not be able to vote for another 21 years.
Roberts mounted his large camera on the side of a larger “guide telescope” that was rigged in such a way that it would follow the rotation of the Earth, which was necessary for the extremely long exposure time needed to photograph something so far away, so dim, so small in the sky.
I say Roberts mounted a large camera — this was actually a reflecting telescope modified to take a photographic plate (a sheet of glass with light-sensitive silver salts painted on it) at the point where its primary mirror focused, enabling him to get pictures of stars much clearer than most other photographers of the day. No holding a lens up to a lens up to a mirror for him.
This particular photograph was the first image showing that the “nebula” had a spiral shape, which then sent astronomers scrambling to find an explanation why. Billions of stars, they eventually concluded. Solar systems practically beyond imagining.