What Exactly Is a Constellation?

A constellation is an area of night sky containing the space designated by a pattern of stars recognized as a mythical, historical, technological, and zoological image from human antiquity.

 Constellation means a “collection of stars,” but specifically, a constellation includes every star, visible and not visible, within a bordered area determined by a pattern humans recognize. Therefore, a constellation is an arbitrarily defined place in the sky, identified by a recognizable pattern of visible stars.

 Sidereal Sidebar: Fanciful drawings of animals, tools, and humans over star charts was never at all useful for recognizing actual constellations <https://upload.wikimedia.org/wikipedia/commons/thumb/4/45/Orion_constellation_Hevelius.jpg/572px-Orion_constellation_Hevelius.jpg>. So taking the names of the constellations as guides, the brilliant H.A. Rey, creator of Curious George, depicted the image named in that region of sky as recognizable stick figures, easily identifiable to contemporary star-gazers. Rey’s work even impressed Albert Einstein. To learn the 88 constellations, there is no better book than H.A. Rey’s The Stars: A New Way to See Them.

 In fact, the International Astronomical Union (IAU) has drawn the borders for each of the 88 recognized constellations so that every part of the sky is completely demarcated. Each constellation is defined by starry-mandered (yup, I just minted that word) shapes in order to include every part of the sky with one constellation or another. Go, look: https://in-the-sky.org/data/charts/constellations_map_equ110112.png

 The edges of only a few constellations are recognizable geometric shapes, like the square that contains the constellations Canis Major, the big dog, or Sextans, the sextant, which both are boxes like Colorado. A few resemble shapes of other American states; for instance, Corvus, the crow, recalls a Utah rotated 180 degrees. Some seem whimsical, like Triangulum Australe, the Southern Triangle, which looks like the ziggurat of a Mayan temple (Triangle> Pyramid> Ziggurat: get it?).

 Others describe shapes that inspired me to create the word “starry-mander” (without the despicable earthbound political implications) because the boundaries were designed only to contain a section of sky identified by the constellation: Eridanus, the river, is my favorite; a second favorite is the bordering constellation, Horologium, the clock.

 My personal astrophysicist Neil deGrasse Tyson bids me regularly to keep looking up, and I will pass along the good advice with a twist: If you’re looking for the sky, look up. If you want to learn the constellations, look to H.A. Rey. And remember, if you want to see the light of stars, first, you must seek the darkness.