Book Shelf Astronomy

There is a practice in astronomy of identifying different types of stars by observing their absorption spectra. Stars produce light across the entire visible spectrum and create what astronomers refer to as a continuous spectrum. This light passes through a thin layer of gas on the outside of the star before it reaches us. Some of the light from the atoms emitted by the star are absorbed in this thin layer of gas and cause black lines to appear over the continuous spectrum. When these black lines appear, it is no longer called a continuous spectrum, but instead is called an absorption spectrum. These black lines that appear on an absorption spectrum are important to astronomers because they provide clues about what the star is composed of.

Gases emit energy in the form of light when electricity passes through them. The color of this light is determined by what elements are within the gas. For example, neon gas always produces a reddish-orange color light, while xenon always creates a blueish-white kind of light. This is the same reason why street lights might appear yellow (due to their use of high-pressure sodium) while some headlights appear blue and blindingly bright (due to their use of xenon). Scientists are able to deduce what a given star is comprised of and what its stellar class is by examining the black lines on an absorption spectrum and determining what colors are missing.

Astronomer Annie Jump Cannon is one of the most well-known astronomers to use optical spectra to identify stars and employed it in her creation of the O-M stellar classification system, which is still used to this day. Cannon classified somewhere in the ballpark of 350,000 stars via optical spectra and was so proficient at reading spectra that she could classify hundreds of stars an hour. More information about Cannon, as well as the other women and men who were responsible for cataloging our universe, can be found in the books “The Glass Universe” and “Starlight Detectives.”

There are a lot of similarities between the color spectrum of stars and the color of the spines of books. For example, books within the gardening section share a lot of similar traits, such as their spines being shades of green or pastel colors.

On the other hand, most books about boating typically have blue spines. By looking at the spectrum of colors present on a shelf, you’ll find you might be able to identify the section they are shelved within in the same way astronomers are able to identify star composition through absorption spectrums. Below are nine spectrums I created by taking the most common color present in the spine of each book on the shelf. I then reorganized the colors to be in the same order as the visible spectrum. Are you able to determine which of the below categories correspond with each shelf spectrum? Scroll all the way to the bottom to find the answers!