What are Constellations?

The term constellation is one that is often misunderstood.  Many people think it is a recognizable pattern in the sky consisting of bright stars.  Although that is an approximate definition of a constellation, the actual answer to the question is a bit more complicated.  A constellation is a set boundary on the celestial sphere defined by the International Astronomical Union.  As shown below in the official "Sky and Telescope" map of Lyra, the boundaries extend to the area highlighted in white.  The pattern of the Lyre forms only part of the constellation.  As shown in the image below, when astronomers refer to Messier 56 (M56) or Messier 57 (M57) they will say they are found in the constellation Lyra.

Lyra

Another interesting thing to note is that calling the Big Dipper a constellation is incorrect.  The Big Dipper is merely a shape in a larger constellation known as Ursa Major.  When shapes are found within constellations or across the boundaries of several constellations they are called asterisms.  There are many examples of asterisms: The Big Dipper, The Little Dipper, The Summer Triangle, Belt of Orion, The Coathanger, Kemble's Cascade, etc.

Most of the bright stars in a constellation can be viewed with the naked eye, however, the dimmer stars can mostly be seen through a set of binoculars.  Deep-sky objects such as a the Messier Objects will require a telescope.  The image below shows my attempt to map Lyra with my naked eye(black dots) and binoculars(orange dots).  The Greek letters attached to each star are based on the Bayer System presented earlier in the week at:

http://simonjastronomy.blogspot.ca/2017/01/explore-universe-alpha-capricorni.html

Lyra Mapping

I have recently updated how I do constellation mapping as shown with Taurus below.

Taurus Constellation Map

All of these stars were observed with the naked eye or binoculars.  The distances between the stars are to scale as well the size of the dot represents the apparent magnitude.  This is a really good exercise for learning the constellations and how to get around them with optical aid.