Curated category
Concepts in astronomy
- SupernovaA supernova is a powerful and luminous explosion of a star. This event occurs during the last evolutionary stages of a massive star or when a white dwarf is…
- Big BangIn 1922, Russian mathematician Alexander Friedmann derived equations from Einstein's field equations that suggested the universe might be expanding.
- Black holeIn 1784, John Michell published a letter suggesting that some stars could be so massive and dense that light would never escape their gravity.
- Cosmic inflationIn 1978, particle physicist Alan Guth began investigating why no magnetic monopoles appeared in the universe. He worked at Cornell University when he…
- Dark energyIn 1917, Albert Einstein introduced a term into his field equations of general relativity. He labeled this term with the Greek letter Lambda (Λ).
- UniverseTime began at zero, a moment known as the Planck epoch. This brief period extended from time zero to one Planck time unit of approximately 10 minus 43…
- Gravitational waveOliver Heaviside proposed the existence of gravitational waves in 1893. He used an analogy between the inverse-square law of gravitation and electrostatic…
- CometThe solid core of a comet is known as the nucleus. It measures from a few hundred meters to tens of kilometers across. These nuclei are loose collections of…
- GalaxyThe word galaxy comes from the Greek term for milky, a direct reference to the Milky Way band visible in our night sky. Early astronomers like Democritus…
- PlanetIn August 2006, the International Astronomical Union voted to reclassify Pluto as a dwarf planet. This decision changed the count of planets in our Solar…
- CosmogonyIn ancient Greece, thinkers developed a cosmogony focused on the origin of matter, space, and time. This transition from Chaos to Cosmos formed a form of…
- Light-yearThe International Astronomical Union established the light-year as a precise unit of length in 1984. This definition relies on two fixed constants: the speed…
- Interstellar mediumThe space between stars is not empty. It holds matter and radiation that astronomers call the interstellar medium. This substance includes gas in ionic…
- Stellar nucleosynthesisIn the year 1920, Arthur Eddington stood before a scientific community that viewed stars as eternal furnaces burning coal or gas.
- StarA star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun, which provides daylight and appears as a disk…
- Newton's law of universal gravitationOn the 5th of July 1687, Isaac Newton published his work Philosophiæ Naturalis Principia Mathematica. This text combined his laws of motion with new…
- Gravitational lensIn 1784, Henry Cavendish wrote an unpublished manuscript suggesting that Newtonian gravity could bend starlight around a massive object.