- The International Astronomical Union recognizes 88 constellations today. Descriptions of the constellations were formalized in the early 1900s with the hopes of being able to identify stars that shone unsteadily (sometimes brightly, sometimes dimly). Astronomers also wanted a better way to track their discoveries. By defining boundaries of constellations, they divided the sky into a more recognizable space.
- Asterisms are groups of stars forming patterns or shapes that usually do not fall within the boundaries of any constellation. The Big Dipper is one example. Asterisms tend to be simpler than constellations, but sometimes they can be a segment of a constellation.
- Constellations are physically defined by established sky coordinates (a pinpointed location), although they may be commonly identified by well-known shapes formed by stars within them. Stars within constellations are not necessarily close to one another in space. Rather, the way we see the stars from Earth determines whether or not they are part of one constellation or another. The appearance of a star will vary according to its brightness and/or distance from earth.
- Constellations have Latin names and are referred to nominatively when the constellation as a whole is referenced. A modified, two-word form that draws on the constellation name is used to refer to a star within a constellation. For example, the Alpha star in the Cancer constellation is called Alpha Cancri.
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