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Carnegie Supernova Project
The Carnegie Supernova Project is a supernova observing program at Las Campanas Observatory in Chile, started in 2004 to study nearby supernovae and dark energy.
Carnegie-Chicago Hubble Program
The Carnegie-Chicago Hubble Program, led by Wendy Freedman, measures the Hubble constant by calibrating Type Ia supernovae with red giant stars, finding values between the Planck and SH0ES estimates.
Cassegrain telescope
The Cassegrain telescope is a reflecting telescope in which a convex secondary mirror folds light back through a hole in the primary, giving a compact tube; the design was published in 1672.
Celestial globe
A celestial globe is a spherical model of the heavens with stars and constellations plotted on the outside, showing a view from outside the sky, and used to teach astronomy.
Celestial sphere
The celestial sphere, also called the celestial dome, is an imaginary sphere centered on the Earth onto which celestial bodies appear to lie, mapped with right ascension and declination.
Centaurus A
Centaurus A, also designated NGC 5128, is a giant elliptical galaxy about 11 million light-years away and the nearest radio galaxy, containing the closest active galactic nucleus to Earth.
Cerro Pachón
Cerro Pachón is a mountain in the Coquimbo Region of northern Chile, on the edge of the Atacama Desert, that hosts the Gemini South, SOAR, and Vera C. Rubin Observatory telescopes.
Cerro Paranal
Cerro Paranal is a mountain in Chile's Atacama Desert, about 120 km south of Antofagasta, hosting the ESO Paranal Observatory and its Very Large Telescope.
Cerro Tololo
Cerro Tololo is a 2,200-meter mountain in Chile's Coquimbo Region, 450 km north of Santiago, hosting the Cerro Tololo Inter-American Observatory, whose Víctor M. Blanco Telescope has been a leading southern-hemisphere research site since 1965.
Cerro Tololo Inter-American Observatory
The Cerro Tololo Inter-American Observatory (CTIO) is a complex of optical astronomical telescopes on Cerro Tololo in northern Chile, at an altitude of 2,200 meters.
Chandra Deep Field-North
Chandra Deep Field-North is a deep X-ray survey of the Hubble Deep Field-North region in Ursa Major, made with NASA's Chandra X-ray Observatory with about 2 megaseconds of exposure.
Chandra Deep Field-South
The Chandra Deep Field-South (CDF-S) is a small sky patch in Fornax with about 7 million seconds of Chandra X-ray exposure, the most sensitive X-ray view of the distant universe.
Chandra X-ray Observatory
The Chandra X-ray Observatory, originally named the Advanced X-ray Astrophysics Facility, is a NASA X-ray astronomy satellite launched in 1999, one of its four Great Observatories.
Changing-look AGN
A changing-look AGN is an active galactic nucleus whose broad emission lines appear or disappear within months to years, switching it between Type 1 and Type 2.
Chaotic inflation
Chaotic inflation is a scenario in cosmological inflation proposed by Andrei Linde in 1983, in which inflation arises naturally from chaotic initial conditions without special tuning.
Chaplygin gas
Chaplygin gas is a hypothetical exotic fluid in cosmology with negative pressure, introduced in 2001 as an alternative to quintessence and a candidate for unifying dark matter and dark energy.
CHIME/FRB
CHIME/FRB is the fast radio burst detection project of the CHIME radio telescope at the Dominion Radio Astrophysical Observatory in British Columbia, commissioned in 2017.
CHIME/FRB Catalog 1
CHIME/FRB Catalog 1 is the first fast radio burst catalog from the CHIME telescope, documenting 536 bursts observed at 400–800 MHz from July 2018 to July 2019.
Chinese Space Station Telescope
The Chinese Space Station Telescope, also called Xuntian, is a planned two-meter optical space telescope China will fly alongside the Tiangong space station to survey billions of galaxies.
Chronology of the universe
The chronology of the universe, also called the timeline of the universe, divides cosmic history into epochs from the Big Bang 13.8 billion years ago to today.
Circinus Galaxy
The Circinus Galaxy is a spiral galaxy about 13 million light-years from Earth, discovered in 1977 and hosting the nearest known Seyfert type 2 nucleus.
Circularly polarized light detection
Circularly polarized light detection, or circular polarimetry, measures the circular component of polarization in light from stars and planets, probing magnetic fields and cloud scattering since 1970.
CMB angular power spectrum
The CMB angular power spectrum measures cosmic microwave background temperature fluctuations by angular size on the sky; its acoustic peaks encode the universe's geometry and composition.
CMB circular polarization
CMB circular polarization is a hypothetical Stokes V component of the cosmic microwave background's polarization, constrained only by upper limits because it is never detected.
CMB cold spot
The CMB cold spot, or WMAP Cold Spot, is an unusually cold region in the cosmic microwave background in the constellation Eridanus, found in WMAP data.
CMB delensing
CMB delensing is the removal of gravitational-lensing distortions that intervening matter imprints on cosmic microwave background maps, mainly to reduce lensing B-modes that limit primordial gravitational-wave searches.
CMB dipole
The CMB dipole is the largest temperature anisotropy in the cosmic microwave background, about 3.36 mK, caused by the Solar System's motion at roughly 370 km/s.
CMB lensing reconstruction
CMB lensing reconstruction is the statistical estimation of the gravitational lensing potential that distorts the cosmic microwave background, using quadratic estimators of temperature and polarization correlations.
CMB polarization
CMB polarization is the linear polarization of the cosmic microwave background, first detected in 2002, whose B modes are a sought signature of primordial gravitational waves from inflation.
CMB-S4
CMB-S4 (Cosmic Microwave Background Stage 4) was a proposed next-generation experiment, planned by the Department of Energy and NSF for the South Pole and Chile, canceled in 2025.