Short answers, pulled from the story.
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos, using mathematics, physics, and chemistry to explain their origin and evolution. Its objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets. More generally, it studies everything that originates beyond Earth's atmosphere.
Astronomy is the scientific study of celestial objects, while astrology is the belief system claiming that human affairs correlate with the positions of celestial objects. The two fields share a common origin but became distinct, with astronomy supported by physics and astrology not.
Astronomy and astrophysics are broadly synonymous in modern usage and are often used interchangeably. Astronomy studies objects and matter outside the Earth's atmosphere and their physical and chemical properties, while astrophysics deals with the behavior, physical properties, and dynamic processes of celestial objects. In some usage astronomy is the qualitative study and astrophysics the physics-oriented version.
Edwin Hubble proved in 1922 to 1923 that Andromeda, Triangulum, and other spiral nebulae were entire galaxies outside our own, using Cepheid variable stars observed with the Hooker Telescope. This showed the universe consists of a multitude of galaxies. The existence of galaxies as groups of stars was only demonstrated in the 20th century.
Cosmic microwave background radiation, discovered in 1965, settled the evidence for the Big Bang. Earlier support came from Hubble's 1929 observation that galaxies move away from Earth with velocity proportional to distance, and from big bang nucleosynthesis models built in the late 1940s and early 1950s. Georges Lemaitre had expounded the Big Bang concept in 1927.
Astronomy is one of the few sciences in which amateurs play an active role, especially in the discovery and observation of transient events. Amateur astronomers have helped find new comets, made occultation measurements to refine the orbits of minor planets, and observed variable stars. Karl Jansky, a pioneer of amateur radio astronomy, discovered a radio source at the centre of the Milky Way.
Observational astronomy is categorized by the region of the electromagnetic spectrum being observed, including radio, infrared, optical, ultraviolet, X-ray, and gamma-ray astronomy. Astronomers also use non-electromagnetic methods such as neutrino astronomy and gravitational-wave astronomy. LIGO made its first gravitational-wave detection on the 14th of September 2015 from a binary black hole.