In deep space, there are numerous glowing patches of light which astronomers called nebulae, the Latin word for clouds. Many of these objects are just that: glowing clouds of gas. Many others are not, but with only the naked eye to guide them, early astronomers could not distinguish any difference, so every glowing patch of light was called a nebula.

One of the earliest-discovered nebulae was located in the constellation Andromeda. It had been known as far back as 905 a.d. and was called the "Little Cloud." The first telescopic observation is credited to Simon Mayr (1573-1624) in 1611 or 1612. Later Lord Rosse (1800-1867) used his huge telescope to observe many nebula, many of which showed an odd spiral structure.

It was not until Edwin Powell Hubble analyzed Cepheid variable stars in 1923 in the Andromeda nebula that its true nature was revealed; it was a gigantic spiral galaxy hundreds...