Space EncyclopediaWIKI

Decode the universe. A curated glossary of astronomical terms and cosmic phenomena.

Black Hole

Cosmology

A region of spacetime where gravity is so strong that nothing, including light and other electromagnetic waves, has enough energy to escape it.

Detail:Black holes are formed when massive stars collapse at the end of their life cycle. Supermassive black holes exist at the center of most galaxies, including our own Milky Way (Sagittarius A*).

Supernova

Stars

A powerful and luminous explosion of a star. It occurs during the last evolutionary stages of a massive star or when a white dwarf is triggered into runaway nuclear fusion.

Detail:A supernova can briefly outshine an entire galaxy, radiating as much energy as the Sun is expected to emit over its entire life span. The explosion expels much or all of a star's material at a velocity of up to 30,000 km/s.

Exoplanet

Planetary Science

A planet outside our solar system. The first evidence of an exoplanet was noted in 1917, but is was not recognized as such.

Detail:As of 2024, there are over 5,000 confirmed exoplanets. They come in many varieties, including "Hot Jupiters", "Super-Earths", and potentially habitable worlds in the Goldilocks zone.

Dark Matter

Cosmology

A hypothetical form of matter that is thought to account for approximately 85% of the matter in the universe.

Detail:Dark matter does not interact with electromagnetic radiation (light), making it invisible. Its existence is inferred from its gravitational effects on visible matter, such as the rotation speeds of galaxies.

Nebula

Stars

A giant cloud of dust and gas in space. Some nebulae come from the gas and dust thrown out by the explosion of a dying star, such as a supernova.

Detail:Other nebulae are regions where new stars are beginning to form ("star nurseries"). The Pillars of Creation in the Eagle Nebula is one of the most famous examples.

Quasar

Cosmology

An extremely luminous active galactic nucleus (AGN). It consists of a supermassive black hole surrounded by a gaseous accretion disk.

Detail:Quasars are among the brightest objects in the universe, outshining their entire host galaxies. They are powered by the accretion of material onto supermassive black holes.

Light Year

Units

A unit of length used to express astronomical distances. It is the distance that light travels in a vacuum in one year.

Detail:One light year is approximately 9.46 trillion kilometers (5.88 trillion miles). For example, the nearest star to Earth (Proxima Centauri) is about 4.24 light years away.

Event Horizon

Physics

A boundary around a black hole beyond which no light or other radiation can escape.

Detail:Accepting the general theory of relativity, the event horizon is the point of no return. Any object or radiation crossing this boundary is inevitably pulled into the black hole.

Asteroid Belt

Solar System

A torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars.

Detail:It contains a great many solid, irregularly shaped bodies, of many sizes but much smaller than planets, called asteroids or minor planets. The dwarf planet Ceres is the largest object in the belt.

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