640 articles
1973 Concorde eclipse flight
The 1973 Concorde eclipse flight was an airborne mission in which Concorde prototype 001 chased the Moon's shadow over Africa, achieving a record 74 minutes of totality.
21-cm cosmology
21-cm cosmology is the branch of observational cosmology that uses the 21-centimeter line of neutral hydrogen, redshifted from the early universe, to map the cosmic dark ages, the Epoch of Reionization, and later structure.
3.5 keV X-ray line
The 3.5 keV X-ray line is an unidentified X-ray emission line reported in 2014 in galaxy clusters and proposed as a signal of decaying sterile neutrino dark matter.
3C 273
3C 273 is a quasar in the constellation Virgo, recognized in 1963 as the first quasar ever identified, with a jet about 300,000 light-years long and the power of thousands of galaxies.
3C 279
3C 279 is a flat-spectrum radio quasar in Virgo and a prototypical blazar, the first object in which apparent superluminal motion was detected, in 1971.
3C 286
3C 286, also known as J1331+3030 or B1328+307, is a compact steep-spectrum quasar at redshift 0.849, the Very Large Array's prime flux density calibrator for over half a century.
3C 345
3C 345 is a bright, variable blazar quasar in Hercules about 5.5 billion light-years away, a core-dominated superluminal radio source monitored optically since the 1960s.
3C 390.3
3C 390.3, also cataloged as B1845+797, is a nearby broad-line radio galaxy whose double-peaked emission lines come from an accretion disc around a supermassive black hole.
3C 454.3
3C 454.3, also cataloged as PKS 2251+158, is a flat-spectrum radio quasar, a type of blazar, in Pegasus at redshift 0.859 that repeatedly became the sky's brightest gamma-ray source.
3C 48
3C 48 is a radio-loud quasar, the 48th entry in the Third Cambridge Catalogue of radio sources, whose 1963 redshift of z = 0.37 helped solve the puzzle of the radio stars.
4C 11.69
4C 11.69, better known as the blazar CTA 102, is a flat-spectrum radio quasar whose 2016 outburst made it briefly the brightest gamma-ray source in the sky.
4MOST
4MOST (4-meter Multi-Object Spectroscopic Telescope) is a wide-field, fiber-fed optical spectrograph on ESO's VISTA telescope at Paranal Observatory in Chile, which achieved first light in 2025.
55 Cancri e
55 Cancri e, also known as Janssen, is a super-Earth exoplanet discovered in 2004 orbiting the star 55 Cancri about 41 light-years away in the constellation Cancer.
8C 0716+714
S5 0716+714, also known as 8C 0716+714, is a BL Lacertae object, a type of blazar, in the constellation Camelopardalis. Discovered in 1979, it is known for strong variability.
A Brief History of Time
A Brief History of Time is a 1988 popular-science book by Stephen Hawking that explains the Big Bang, black holes, and the nature of space and time for general readers.
Abell 2744
Abell 2744, nicknamed Pandora's Cluster, is a massive galaxy cluster about 3.5 billion light-years away that formed from a collision of at least four smaller clusters.
Abell 426
Abell 426, also designated ACO 426, is the Perseus Cluster, a rich nearby galaxy cluster in Perseus and the X-ray brightest cluster in the sky, about 300 million light-years away.
Absolute magnitude
Absolute magnitude, also called intrinsic brightness, is a measure of the intrinsic brightness of a celestial object, defined as its apparent magnitude when viewed from 10 parsecs.
Accelerating expansion of the universe
The accelerating expansion of the universe, also called cosmic acceleration, is the 1998 discovery from distant Type Ia supernovae that the universe's expansion is speeding up, attributed to dark energy.
ACO 1367
ACO 1367, also written Abell 1367 and known as the Leo Cluster, is a nearby, spiral-rich cluster of galaxies in the constellation Leo about 92 megaparsecs away.
ACO 1656
ACO 1656, better known as the Coma Cluster (Abell 1656), is a nearly spherical cluster of over 1,000 galaxies in Coma Berenices, about 300 million light-years from Earth.
ACO 1689
ACO 1689, also cataloged as Abell 1689, is a massive, luminous galaxy cluster at redshift z = 0.183, one of the most powerful known gravitational lenses.
ACO 1795
ACO 1795, also known as Abell 1795, is a nearby, X-ray bright galaxy cluster in Boötes with a strong cool core and a 200,000-light-year cooling filament.
ACO 2199
ACO 2199, also written Abell 2199, is a rich, regular cluster of galaxies in the constellation Hercules, centered on the giant galaxy NGC 6166, some 400 million light-years from Earth.
Acoustic peaks
Acoustic peaks are peaks in the cosmic microwave background power spectrum from sound waves in the early universe; they measure the universe's geometry and composition.
Active galactic nucleus
An active galactic nucleus (AGN) is a galaxy's bright central region, powered by gas and dust falling into a black hole millions to billions of solar masses.
ACTPol
ACTPol (Atacama Cosmology Telescope Polarimeter) was a receiver on the six-meter Atacama Cosmology Telescope in Chile that measured cosmic microwave background polarization from 2013 until 2016.
Adaptive optics
Adaptive optics is a real-time technique that measures and corrects atmospheric blur in telescope images with a deformable mirror, restoring diffraction-limited sharpness; it was proposed by H. W. Babcock in 1953.
Advanced ACTPol
Advanced ACTPol, also known as AdvACT, was the second-generation polarization receiver on the Atacama Cosmology Telescope in Chile, which replaced ACTPol and observed the cosmic microwave background from 2016 to 2022.
Advanced Virgo
Advanced Virgo is the second-generation, kilometer-scale gravitational-wave laser interferometer at Cascina near Pisa, Italy, operated by the Virgo Collaboration; with LIGO it localized sources like GW170814 to 60 deg².