You are looking through a very old astronomy book,and you find the Messier object M31 referred to as the Andromeda Nebula.You might suspect that this book was written before:

Question

Quizplus · Accepted Answer

M31 was officially recognized as a galaxy in 1924 thanks to the work of astronomer Edwin Hubble, before which it was commonly referred to as the Andromeda Nebula. Therefore, a book referring to it as the Andromeda Nebula was likely written before 1924.

You Are Looking Through a Very Old Astronomy Book,and You