The night sky is populated by thousands of objects of various shapes and sizes. It is not always easy to find your way around. Here are a few elements to help you understand what kind of objects you are dealing with and how to classify them:

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Solar systemEverything within our immediate space environment: the planets, the Sun, the Moon, comets, and associated phenomena such as eclipses or auroras (polar lights).
Stellar objectsIn relatively “nearby” space, the term stellar encompasses everything related to stars on their main sequence—meaning during their “adult” life, powered by the nuclear fusion of hydrogen. This includes individual stars (variable, binary, or colored stars) as well as stellar associations, such as open clusters or globular clusters.
NébulaeObjects with a “diffuse” appearance within a galaxy, which are primarily gas clouds, most often subjected to electromagnetic radiation. They can be:
1. Molecular or cold: These are dark nebulae, which are found everywhere in the universe.
2. Hot or ionized, emitting or reflecting light: These are generally associated with star formation or stellar youth. This is notably the case for H II regions within galaxies.
3. Associated with the end of a star’s life: Such as planetary nebulae, Wolf-Rayet bubbles, or supernova remnants (SNRs). These can be referred to as “stellar ejection nebulae.”
GalaxiesEverything that lies beyond our own Milky Way. This includes individual galaxies, both nearby and distant, as well as all galaxy groupings—whether they are compact groups or spread out into clusters and superclusters—where interactions between galaxies take shape. Gravity is the dominant force here, manifesting through tidal forces or gravitational lensing.