Astronomy

Astronomy is the scientific study of celestial objects, cosmic phenomena, and the structure and evolution of the universe.

Astrophysics applies physical laws to explain the properties, behavior, origins, and evolution of celestial objects and the universe.

Baryon acoustic oscillations are relic patterns of primordial sound waves in cosmic matter, used as a standard ruler to measure the universe’s expansion.

The Big Bang model describes the universe’s expansion and cooling from an early hot, dense state, supported by cosmic expansion, background radiation, and primordial element abundances.

A binary star is a system of two gravitationally bound stars whose orbital motion reveals their masses and can strongly influence their evolution.

A black hole is a region of spacetime bounded by an event horizon, beyond which nothing can escape to the outside universe.

The cosmic microwave background is relic radiation from the early universe, whose spectrum and spatial variations reveal its thermal history, composition, and structure.

A constant term in Einstein’s gravitational equations, equivalent to uniform vacuum energy, whose positive value can drive accelerated cosmic expansion.

Cosmology studies the universe as a whole, including its origin, composition, large-scale structure, evolution, and possible future.

Dark energy is the unknown component invoked to explain the accelerating expansion of the universe, commonly modeled as a cosmological constant.

Dark matter is an unseen component of the universe inferred from gravitational effects, whose physical nature remains unidentified.

Earth is the third planet from the Sun and the only astronomical object known to support life. It is the densest planet in the Solar System and is mostly covered by liquid water.

A galaxy is a gravitationally bound system of stars, gas, dust, and usually dark matter, forming a major component of cosmic structure.

The Hubble constant is the present-day fractional expansion rate of the universe, relating cosmic recession velocities to distances and setting a fundamental cosmological scale.

Johannes Kepler was a German astronomer and mathematician who formulated three laws of planetary motion and contributed to optics, geometry, and astronomical calculation.

Jupiter is the largest planet in the Solar System, a gas giant whose mass, atmosphere, magnetic field and moons shape the wider solar system.

The standard cosmological model describing an expanding universe with a cosmological constant, cold dark matter, ordinary matter, and radiation.

Mars is the fourth planet from the Sun, a cold, dry, dusty world that is the most-explored planet after Earth and a central target for the search for past life and future human spaceflight.

The Milky Way is the barred spiral galaxy that contains the Solar System and Earth, with hundreds of billions of stars, a central black hole, and a dark matter halo.

The Moon is Earth’s only natural satellite, a rocky world whose orbit, surface, and geological history illuminate the evolution of the Earth–Moon system.

Neutrino astronomy studies the Sun, stellar explosions, and cosmic particle accelerators by detecting neutrinos arriving from space.

A neutron star is an exceptionally dense stellar remnant whose structure is governed by gravity, quantum physics, and nuclear interactions.

Nicolaus Copernicus was a Renaissance astronomer whose mathematical model of a moving Earth transformed European astronomy.

A planet is a body that orbits a star, has enough mass to be rounded by its own gravity, and, in the Solar System, has cleared its orbital neighbourhood.

Ptolemy was a second-century scholar whose writings shaped astronomy, geography, astrology, optics, and music theory for many centuries.

Cosmological recombination is the formation of neutral atoms in the cooling early universe, which enabled cosmic microwave background photons to travel largely freely.

Redshift is an increase in radiation’s observed wavelength caused by relative motion, gravitation, or cosmic expansion.

The Solar System comprises the Sun and its gravitationally bound planets, moons, smaller bodies, and interplanetary material.

A star is a self-gravitating, luminous astronomical object whose active life is powered primarily by nuclear fusion.

The Sun is the hydrogen-fusing star at the center of the Solar System and the principal source of energy for Earth’s surface.

A supernova is a powerful stellar explosion that ejects matter, produces a luminous transient, and contributes to the chemical evolution of galaxies.

A white dwarf is a dense stellar remnant supported by electron degeneracy pressure that usually shines by gradually releasing stored heat.