天文学英語：必須語彙とフレーズ

"main sequence"

The band on the Hertzsprung–Russell diagram where stars spend most of their lives fusing hydrogen into helium in their cores

"Our Sun is a main sequence star and will remain in this stable phase for another five billion years."

"nuclear fusion"

The process by which lighter atomic nuclei combine under extreme pressure and temperature to form heavier nuclei, releasing enormous amounts of energy

"The energy that makes stars shine comes from nuclear fusion occurring at temperatures exceeding 15 million degrees Celsius in the stellar core."

"stellar luminosity"

The total amount of energy radiated per second by a star, usually expressed in units of solar luminosity

"Astronomers measured the stellar luminosity by combining the star's apparent brightness with its known distance from Earth."

"red giant"

An evolved, cool star with a greatly expanded outer envelope that a Sun-like star becomes after exhausting hydrogen in its core

"When our Sun becomes a red giant in about five billion years, its outer layers will engulf the orbits of Mercury and Venus."

"supernova"

A catastrophic stellar explosion that occurs when a massive star exhausts its fuel or a white dwarf accretes too much mass, briefly outshining an entire galaxy

"The supernova remnant observed by the team was still expanding at thousands of kilometres per second, 300 years after the original explosion."

"neutron star"

The extremely dense remnant left after a massive star undergoes a supernova, composed almost entirely of neutrons and packed into a sphere roughly 20 km across

"The neutron star was detected through its regular pulses of radio emission, making it one of the most precisely timed objects in the universe."

"stellar parallax"

The apparent shift in a star's position against the background sky as Earth orbits the Sun, used to measure distances to nearby stars

"The Hipparcos satellite measured the stellar parallax of over 100,000 stars to build the most accurate three-dimensional map of the solar neighbourhood at the time."

"spectral classification"

A system that categorises stars into types (O, B, A, F, G, K, M) based on the absorption lines in their spectra, which reflect surface temperature

"The star's spectral classification of G2V confirmed that it was almost identical in temperature and size to our own Sun."

"Big Bang"

The prevailing cosmological model describing the origin of the universe as an extremely hot, dense state approximately 13.8 billion years ago that has been expanding ever since

"Evidence for the Big Bang includes the cosmic microwave background radiation, the observed expansion of the universe, and the primordial abundances of hydrogen and helium."

"cosmic microwave background"

The faint thermal radiation that permeates all of space, representing the afterglow of the early hot universe about 380,000 years after the Big Bang

"Tiny fluctuations in the cosmic microwave background mapped by the Planck satellite revealed the seeds of the large-scale structure we see today."

"dark energy"

A hypothetical form of energy that pervades all of space and is thought to be responsible for the observed accelerated expansion of the universe

"Observations of distant Type Ia supernovae in 1998 provided the first strong evidence that dark energy was driving the universe to expand at an ever-increasing rate."

"dark matter"

An invisible form of matter that does not interact with electromagnetic radiation but exerts gravitational effects, making up about 27% of the total energy content of the universe

"The rotation curves of spiral galaxies remain flat far beyond the visible disk, which is widely interpreted as evidence for an extended halo of dark matter."

"redshift"

The increase in wavelength of electromagnetic radiation from an object moving away from the observer, used to measure cosmic distances and recession velocities

"The quasar's extreme redshift of z = 7.1 indicated that its light was emitted when the universe was less than 800 million years old."

"Hubble constant"

The rate at which the universe is currently expanding, expressed as the recession velocity per unit distance between galaxies

"Tensions between different measurements of the Hubble constant have become one of the most important unsolved problems in modern cosmology."

"cosmic inflation"

A theoretical period of exponentially rapid expansion in the very early universe, proposed to explain the large-scale uniformity and flatness of space

"The near-perfect isotropy of the cosmic microwave background is one of the key pieces of evidence cited in support of cosmic inflation."

"large-scale structure"

The network of galaxy clusters, filaments, sheets, and voids that forms the web-like architecture of the observable universe on the largest scales

"Computer simulations of large-scale structure formation successfully reproduce the observed distribution of galaxies when dark matter and dark energy are included."

"exoplanet"

A planet that orbits a star other than the Sun, detected through methods such as the transit technique or radial velocity measurements

"The Kepler Space Telescope confirmed the existence of thousands of exoplanets by detecting the tiny dimming of starlight as each planet passed in front of its host star."

"habitable zone"

The range of orbital distances from a star within which liquid water could theoretically exist on a planet's surface, sometimes called the Goldilocks zone

"Astronomers announced the discovery of a rocky exoplanet orbiting within the habitable zone of a nearby Sun-like star, making it a candidate for further atmospheric study."

"planetary differentiation"

The process by which a newly formed planet separates into layers of different density, with heavier materials sinking to form a core and lighter materials rising to form a crust

"Seismic data from the InSight lander confirmed that Mars underwent planetary differentiation, revealing a distinct metallic core, mantle, and crust."

"retrograde motion"

The apparent westward movement of a planet against the background stars as seen from Earth, caused by the relative speeds of the two planets in their orbits

"Ancient astronomers were puzzled by retrograde motion of Mars, which Copernicus later explained by placing the Sun at the centre of the solar system."

"tidal locking"

A gravitational effect in which one body always shows the same face to its companion because its rotation period has become equal to its orbital period

"The Moon is tidally locked to Earth, which is why we only ever see one hemisphere from our planet's surface."

"accretion disk"

A rotating disk of gas, dust, or other material that spirals inward toward a central body such as a protostar, black hole, or neutron star

"The accretion disk surrounding the young protostar was dense enough to block visible light but glowed brightly in infrared wavelengths."

"impact cratering"

The process by which meteoroids, asteroids, or comets collide with a planetary surface to form bowl-shaped depressions called craters

"The high density of impact cratering on the lunar highlands indicates that the Moon's surface has not been resurfaced since the early solar system."

"atmospheric escape"

The process by which gas molecules in a planet's upper atmosphere gain enough energy to overcome gravity and escape into space

"Mars lost much of its early atmosphere through atmospheric escape after its protective global magnetic field weakened billions of years ago."

"event horizon"

The boundary surrounding a black hole beyond which nothing — not even light — can escape, marking the point of no return

"The first direct image of a black hole's event horizon was captured by the Event Horizon Telescope in 2019, revealing the shadow of M87's central black hole."

"singularity"

A point of infinite density and zero volume at the centre of a black hole where the known laws of physics break down

"General relativity predicts the existence of a singularity inside every black hole, but physicists believe a complete theory of quantum gravity will resolve this breakdown."

"gravitational lensing"

The bending of light from a distant source around a massive foreground object, predicted by general relativity, which can magnify and distort background images

"Astronomers used gravitational lensing by a galaxy cluster to magnify a distant supernova that would otherwise have been too faint to detect."

"gravitational wave"

A ripple in the fabric of spacetime produced by accelerating massive objects such as merging black holes or neutron stars, travelling at the speed of light

"The LIGO detector registered a gravitational wave signal in 2015 matching the predicted signature of two black holes spiralling together and merging."

"Schwarzschild radius"

The critical radius below which an object must be compressed for it to become a black hole, proportional to its mass

"For the Sun to become a black hole, all of its mass would need to be compressed within its Schwarzschild radius of approximately three kilometres."

"Hawking radiation"

Thermal radiation theoretically emitted by black holes as a result of quantum effects near the event horizon, which would cause black holes to slowly evaporate over immense timescales

"Hawking radiation has never been directly detected because black holes of stellar mass emit it at temperatures many orders of magnitude below the cosmic microwave background."

"tidal disruption event"

An astronomical phenomenon occurring when a star passes close enough to a supermassive black hole to be torn apart by tidal forces, producing a bright flare of radiation

"The optical and X-ray survey detected a tidal disruption event in a dormant galaxy whose central black hole had been quiescent for millions of years."

"spacetime curvature"

The distortion of the four-dimensional fabric of space and time caused by the presence of mass or energy, as described by Einstein's general theory of relativity

"GPS satellites must account for spacetime curvature near Earth's surface to maintain the precision required for accurate navigation."

"angular resolution"

The ability of a telescope to distinguish fine detail, expressed as the smallest angular separation between two objects that can be seen as distinct

"The Hubble Space Telescope's superior angular resolution above the atmosphere enabled it to resolve individual stars in nearby galaxies."

"photometry"

The measurement of the brightness of celestial objects, used to study variable stars, detect exoplanet transits, and monitor transient events

"Precise photometry from the Kepler mission revealed the periodic dimming of thousands of stars caused by orbiting planets blocking a fraction of the starlight."

"spectroscopy"

The analysis of the spectrum of light from a celestial object to determine its chemical composition, temperature, velocity, and other physical properties

"Spectroscopy of the exoplanet's atmosphere during transit revealed absorption features consistent with the presence of water vapour."

"interferometry"

A technique that combines signals from multiple telescopes separated by large distances to achieve an angular resolution equivalent to a single telescope the size of their separation

"Very long baseline interferometry linked radio telescopes across the globe to produce images with resolutions thousands of times sharper than any single dish."

"adaptive optics"

A technology that corrects for the blurring effects of atmospheric turbulence in real time using a deformable mirror controlled by wavefront sensors

"With adaptive optics engaged, the ground-based telescope achieved near-diffraction-limited images rivalling those taken from space."

"multiwavelength astronomy"

The approach of observing celestial objects across multiple regions of the electromagnetic spectrum — from radio waves through X-rays — to gain a complete physical picture

"Multiwavelength astronomy campaigns combining radio, infrared, optical, and X-ray data provided a comprehensive view of the supernova remnant's structure and energetics."

"limiting magnitude"

The faintest apparent magnitude of objects that a given telescope or detector system can reliably detect under specified observing conditions

"The Vera Rubin Observatory's large mirror and wide field of view will push its limiting magnitude deep enough to detect billions of previously unknown faint objects."

"signal-to-noise ratio"

A measure of the strength of an astronomical signal compared to the background noise in the data, which determines the reliability and precision of measurements

"The team took a series of long exposures and co-added the images to improve the signal-to-noise ratio and reveal the faint tidal streams around the galaxy."

"elliptical galaxy"

A type of galaxy with a smooth, featureless ellipsoidal shape, little ongoing star formation, and a predominantly old stellar population

"The giant elliptical galaxy at the centre of the cluster was the product of multiple mergers and contained several trillion stars — ten times the mass of the Milky Way."

"spiral arms"

The curved, star-forming regions that extend outward from the central bar or bulge of a spiral galaxy, containing young stars, gas, and dust

"Traced by its hot blue stars and star-forming regions, the galaxy's spiral arms were clearly resolved in the new deep-field image."

"active galactic nucleus"

An extremely luminous compact region at the centre of a galaxy powered by accretion of matter onto a supermassive black hole, which can outshine the entire host galaxy

"The active galactic nucleus of the quasar emitted more energy per second than a trillion normal stars, making it visible across billions of light-years."

"galactic merger"

The collision and eventual coalescence of two or more galaxies due to mutual gravitational attraction, often triggering bursts of new star formation

"The Antennae Galaxies are a famous pair caught in the middle of a galactic merger, their overlapping disks lit up by thousands of newborn star clusters."

"globular cluster"

A tightly bound, spherical collection of hundreds of thousands to millions of old stars that orbits the outer halo of a galaxy

"Omega Centauri, the largest globular cluster orbiting the Milky Way, contains roughly ten million stars and may be the remnant core of a dwarf galaxy consumed long ago."

"intergalactic medium"

The tenuous gas and plasma that fills the space between galaxies within a galaxy cluster or group, detectable primarily through X-ray emission and absorption of background radiation

"X-ray observatories mapped the hot intergalactic medium permeating the galaxy cluster, whose temperature exceeded tens of millions of degrees."

"stellar population"

A group of stars classified by age and metallicity: Population I stars are young and metal-rich, while Population II stars are old and metal-poor

"The halo of the Milky Way is dominated by Population II stars whose low metallicity indicates they formed from the near-pristine gas of the early universe."

"light-year"

The distance that light travels in one year in a vacuum, approximately 9.46 trillion kilometres, used as the standard unit for expressing astronomical distances

"The Andromeda Galaxy, our nearest large galactic neighbour, lies approximately 2.5 million light-years from the Milky Way."