Astronomy is the study of the physical and chemical properties of large celestial bodies and natural phenomena on such a scale. Objects that are studied in astronomy include, but are not limited to, planets, asteroids, comets, natural satellites, stars, and galaxies.
The study of the behaviour and dynamic processes of said objects is known as astrophysics (a term often used synonymously with astronomy), and the study of their chemical processes is known as astrochemistry. The study of extraterrestrial life is known as astrobiology. The hobby where people look into the sky with the naked eye, binoculars, or small telescopes is known as amateur astronomy, whereas the division of astronomy concerned with taking observations of celestial objects in our observable universe under different parts of the electromagnetic spectrum is called observational astronomy. From observing objects, you can create theoretical models to help explain the processes. The field concerned with doing that is known as theoretical astronomy. Leading theories include the Big Bang, cosmic inflation, general relativity, and the existence of dark matter and dark energy (the current leading mysteries).
The study of the entire Universe and how it is formed on the other hand, is a separate subject called physical cosmology (often called just "cosmology").
Both sciences are similar in the sense that both study very large objects, but are distinct nonetheless. The practice of defining objects larger than the Universe, which is what this wiki revolves around, is known as speculative cosmology (often called just "cosmology" on the wiki), which, unlike astronomy and physical cosmology, does not revolve around observations of discovered objects and instead revolves around making up large structures and organizing them in a hierarchy.
Astronomy is one of the oldest natural sciences, and dates back before recorded history as ancient civilizations would observe the night sky and constellations.
Below describes the specific subfields of astronomy and cosmology, in order of the size of the objects studied.
Planetary astronomy, better known as planetary science is concerned with the formation and properties of, as the name implies, planets. It's scope also includes satellites, minor planets (which includes dwarf planets, asteroids, and centaurs), and comets. The discipline concerned with the geology of those objects is known as planetary geology.
Stellar astronomy is concerned with the formation and properties of stars, which are fundamental to the understanding of our universe. Virtually all naturally-occurring chemical elements heavier than hydrogen and helium are formed within stars, and without stars, we wouldn't exist. The branch concerned with the study of our own Sun is called solar astronomy.
Extragalactic astronomy is concerned with the formation and properties of galaxies, large gravitationally bound collections of stars, gas, dust, and dark matter; along with clusters of stars and nebulae within. The study of the objects in our own galaxy, the Milky Way, is known as galactic astronomy.
Physical cosmology, better known as just cosmology, is the largest domain of astronomy and is concerned with the origin and properties of our Universe, along with its eventual fate. The current standard model of cosmology, the Lambda-CDM model, which is a model of the universe where it contains a cosmological constant, is based on observations of what we can see and current leading theories.
The specific study of the origins and formation of the universe is called cosmogony.
It is not known if anything is outside of our Universe, such as, say, parallel universes in a multiverse of some sorts, nor has it been proven or disproven that there exists a deity that created the universe. Cosmologies that have concepts like those fall into the domain of religious, mythological, or speculative cosmology.