A constellation in a broader sense is a group of stars or asterism that seemingly relate to each other and form a certain image in the sky. Stars are commonly known together whenever they are not physically related and are highly defined. The further the observer moved away from Earth, the more constellations would appear differently from what we see in the sky on Earth. Looking from an extrasolar planet, we would see completely different constellations than from Earth. The appearance of the constellations changes very slowly. This is due to the movement of the stars.
In some constellations, there is a distinctive pattern, which is found in the star maps of connected lines, the lines that connect the individual bright stars. The connectors are used for easier orientation of the observer in the sky.
In a narrower and more precise sense, the constellation is an area of the starry sky with a well-defined position and boundaries, with modern astronomy today distinguishing 88 constellations. In the northern sky, some constellations are based on Ptolemy’s 48 constellations.
Every part of the sky belongs to a constellation, so there is no part of the sky that is not part of a constellation. The constellation also includes all other cosmic objects, such as star clusters, nebulae, and galaxies.
The only star that is not part of any constellation is the Sun, because as it appears to move across the sky, it alternately projects into one of thirteen different constellations, which we call the zodiac constellations. All the planets of the solar system and the Moon are also projected into the animal constellations.
Most of today’s constellations in the northern sky have names derived from Greek mythology.
According to observability:
- about spring
- about summer
- about autumn
- about winter
- not coming out
If the observer is on the earth’s pole, all the constellations are circumpolar for him. If the observer is on the equator, all the constellations are for him coming out and setting for him. If the observer is in any other place, some constellations (or part of them) see all year round, so they are circumpolar, some see only at certain seasons (outgoing) and some never see (outgoing). The closer the observer is to the pole, the fewer constellations he has and the more constellations for him belong to the circumpolar and non-circumferential ones.
According to the passing planes:
- ecliptic – 13 constellations of an animal:
- constellations of the equator of the world
- the constellation of the galactic equator
By origin of the name:
- Ptolemy – original constellations: Andromeda, Northern Crown, …
- Modern: Ruler, Microscope, Fly, …