640 articles
Equinox
An equinox, also called an equinoctial point, is either of the two moments each year when the Sun crosses the plane of Earth's equator, in March and September.
eROSITA
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is a German-built X-ray telescope on the Russian-German SRG mission, launched in 2019 to scan the whole sky.
eROSITA all-sky survey
The eROSITA all-sky survey (eRASS) is the X-ray survey of the entire sky carried out by the eROSITA telescope aboard the Russian-German SRG observatory, beginning in December 2019.
Escape fraction of ionizing photons
The escape fraction of ionizing photons is the fraction of hydrogen-ionizing photons produced in a star-forming galaxy that escapes its gas and dust into the intergalactic medium.
Eternal inflation
Eternal inflation, or the inflationary multiverse, is a class of cosmological scenarios in which exponential expansion never ends everywhere, continuously producing bubble or pocket universes; our observable universe would be one of them.
European Solar Telescope
The European Solar Telescope is a planned 4.2-meter solar telescope at Roque de los Muchachos Observatory on La Palma, Spain, promoted by 26 European research institutions.
European Southern Observatory
The European Southern Observatory, founded in 1962, is an intergovernmental organization of 16 European states that builds and operates observatories in Chile, including the Very Large Telescope.
Event Horizon Telescope
The Event Horizon Telescope is a global network of radio telescopes linked into one Earth-sized virtual telescope, which released the first image of a black hole in April 2019.
Exoplanet
An exoplanet, or extrasolar planet, is a planet orbiting a star other than the Sun. Over 6,000 have been confirmed since the first discovery around a Sun-like star in 1995.
Exoplanet biosignature false-positive framework (abiotic O2)
The exoplanet biosignature false-positive framework for abiotic O2 distinguishes life-produced atmospheric oxygen from oxygen made without life, chiefly on planets orbiting M dwarf stars, using observational tests.
Exoplanet phase curve
An exoplanet phase curve is the measurement of a star-planet system's total brightness as the planet orbits, letting astronomers infer an exoplanet's atmosphere, clouds, winds, and heat distribution without imaging it.
Expansion of the universe
The expansion of the universe is the increase over time of distances between gravitationally unbound galaxies, at the Hubble rate of about 67 to 74 kilometers per second per megaparsec, and accelerating since 1998.
Extremely Large Telescope
The Extremely Large Telescope (ELT) is a 39-meter optical and infrared telescope the European Southern Observatory is building in Chile, to become the world's largest.
Fast radio burst
A fast radio burst is a millisecond flash of radio emission from cosmological distances, first detected in 2007 and now known to come at least partly from magnetars.
Fast radio burst cosmology
Fast radio burst cosmology uses millisecond-duration extragalactic radio pulses as distance probes: each burst's dispersion measure grows with distance, measuring cosmic baryons and the Hubble constant.
Fermi paradox
The Fermi paradox, also called the Fermi-Hart paradox, is the conflict between the expected abundance of alien civilizations and the total lack of evidence for them.
Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph
The Fine Guidance Sensor and Near Infrared Imager and Slitless Spectrograph (FGS/NIRISS) is a Canadian Space Agency instrument on the James Webb Space Telescope that guides pointing and performs near-infrared imaging and spectroscopy.
Fine-tuned universe
The fine-tuned universe is the claim in physics and philosophy that life depends sensitively on the constants of nature; small changes would have prevented life from arising.
First G-APD Cherenkov Telescope
The First G-APD Cherenkov Telescope (FACT) is a Cherenkov telescope on La Palma, Spain, the first with a camera of silicon Geiger-mode photodiodes instead of photomultiplier tubes.
Five-hundred-meter Aperture Spherical Telescope
The Five-hundred-meter Aperture Spherical Telescope, known as FAST or Tianyan, is a 500-meter radio telescope in Guizhou, China, completed in 2016, the world's largest single-dish radio telescope.
FlashCam
FlashCam is a fully digital Cherenkov camera for the medium-sized telescopes of the Cherenkov Telescope Array Observatory, assigned to its southern array site alongside NectarCAM.
Flat-spectrum radio quasar
A flat-spectrum radio quasar (FSRQ) is a blazar whose relativistic jet points near our line of sight, distinguished from BL Lac objects by strong, broad emission lines.
Flux calibration
Flux calibration is the observational procedure in astronomy that converts raw detector counts into physical flux units by comparing observations of standard sources with the science target.
Fractal cosmology
Fractal cosmology is a family of proposals in physical cosmology that the galaxy distribution, or spacetime itself, is fractal; SDSS and WiggleZ surveys find homogeneity beyond roughly 70–100 megaparsecs.
FRB 20190520B
FRB 20190520B is a repeating fast radio burst detected by China's FAST telescope in 2019, co-located with a persistent radio source in a star-forming dwarf galaxy.
Fred Lawrence Whipple Observatory
The Fred Lawrence Whipple Observatory is the largest field research station of the Smithsonian Astrophysical Observatory, located on Mount Hopkins in southern Arizona and established in 1968.
Fred Young Submillimeter Telescope
The Fred Young Submillimeter Telescope (FYST), formerly CCAT-prime, is a 6-meter submillimeter survey telescope on Cerro Chajnantor in Chile, run by a Cornell-led consortium, with first light expected in 2026.
Fundamental plane
The fundamental plane is an empirical scaling relation of elliptical galaxies linking effective radius, surface brightness, and velocity dispersion, established in 1987 and used to measure distances.
Future of an expanding universe
The future of an expanding universe, also called the future of the universe, is the set of end states cosmologists consider, decided by dark energy's nature.
Fuzzy dark matter
Fuzzy dark matter, also called wave dark matter, is a proposed form of dark matter made of ultralight particles that behave collectively as a wave, proposed in 2000.