It is not news that a constellation is a group of stars on the night sky.
But did you know that officially there're only 88 constellations that together cover the entire celestial sphere? And each constellation contains at least a hundred of stars!
All constellations are grouped in 8 constellation families by some defining characteristic, such as proximity on the celestial sphere, common historical origin, or common mythological theme.
Professional astronomers describe stars using a variety of parameters, but we'll explore only three of them:
- distance
- apparent magnitude
- color index
The fist one is the distance to a star from the Sun in parsecs.
The parsec is the most common unit in astrometry. It is equal to about 3.26 light-years (30 trillion km or 19 trillion miles) in length.
The apparent magnitude of a star is a number that is a measure of its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value.
The brightest stars in the night sky were said to be of first magnitude (m = 1), whereas the faintest were of sixth magnitude (m = 6), which is the limit of human visual perception.
It means that the brightest star doesn't equal to the nearest star most of the time. Almost all of the nearest stars are invisible for a human eye.
The color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature.
The smaller the color index, the more blue (or hotter) the object is. Conversely, the larger the color index, the more red (or cooler) the object is.