What’s the farthest object you can see with only your eyes? Unless you live under extremely dark skies unspoiled by light pollution, the answer is the Andromeda Galaxy (M31), located some 2.5 million light-years away. Traveling across such a vast, empty gulf reduces the combined light of M31’s estimated 1 trillion stars to a 4th-magnitude smudge that we can spot just 1.5° west of Nu (ν) Andromedae.
The early 20th century was a watershed moment for the Andromeda Galaxy. In 19