Cosmology and observation

Supernova Legacy Survey

The Supernova Legacy Survey (SNLS) was a five-year observational program at the Canada-France-Hawaii Telescope, begun in 2003, that discovered and monitored hundreds of distant Type Ia supernovae to measure dark energy.

Surface brightness fluctuation distance method

The surface brightness fluctuation (SBF) method, introduced by Tonry and Schneider in 1988, measures galaxy distances from the graininess of unresolved stellar images and helps determine the Hubble constant.

Surface photometry

Surface photometry is the measurement of how a celestial object's light is distributed across its image as surface brightness, the standard way to characterize galaxy structure.

TDCOSMO

TDCOSMO (Time-Delay COSMOgraphy) is an international collaboration, formed from COSMOGRAIL, H0LiCOW, STRIDES, and SHARP, that measures the Hubble constant from time delays between gravitationally lensed quasar images.

Tensor-to-scalar ratio

The tensor-to-scalar ratio, written r, compares the amplitude of primordial gravitational waves to density fluctuations in the early universe, and is a principal observational test of cosmic inflation.

The Cliff (astronomical object)

The Cliff is a distant 'little red dot' found by the James Webb Space Telescope in 2024, proposed to be a 'black hole star' at redshift 3.548.

The Inflationary Universe (book)

The Inflationary Universe is a 1997 popular-science book by MIT physicist Alan Guth, giving his first-hand account of how he developed the theory of cosmic inflation.

Thirty Meter Telescope

The Thirty Meter Telescope (TMT) is a proposed optical-infrared extremely large telescope with a 30-meter segmented primary mirror, planned for the summit of Maunakea in Hawaii.

Tibet ASγ experiment

The Tibet ASγ experiment is a China-Japan air shower observatory at Yangbajing, Tibet, operating since 1990; it reported the first astrophysical photons beyond 100 TeV in 2019.

Time delay interferometry

Time delay interferometry, or delay interferometry, is a data-analysis technique for space-based gravitational-wave detectors like LISA that cancels laser frequency noise by combining time-shifted spacecraft measurements.

Time-delay cosmography

Time-delay cosmography measures the Hubble constant from time delays between gravitationally lensed images of variable sources like quasars, an idea proposed by Søren Refsdal in 1964.

Time-delay integration

Time-delay integration, or drift scanning, is a CCD readout mode where charge shifts across the sensor to match the sky's drift, enabling continuous survey scans.

Time-series photometry

Time-series photometry is the astronomical technique of repeatedly measuring an object's brightness to build a light curve, revealing transiting exoplanets, eclipsing binaries, and pulsating stars.

Tip of the red giant branch

The tip of the red giant branch (TRGB) is a sharp cutoff in the brightness of a galaxy's red giants, used as a standard candle for measuring extragalactic distances.

Tired light

Tired light is a class of non-expanding cosmological models proposed by Fritz Zwicky in 1929, in which redshift comes from photons losing energy in transit rather than cosmic expansion.

TON 618

TON 618, short for Tonantzintla 618, is a hyperluminous, radio-loud quasar near the border of Canes Venatici and Coma Berenices hosting one of the most massive black holes known.

Too big to fail problem

The too big to fail problem in cosmology is the mismatch between simulated massive dark matter subhaloes and the Milky Way's observed satellite galaxies, named in 2011.

Transit light source effect

The transit light source effect is a bias in exoplanet transmission spectroscopy that arises when starspots or faculae make the transited star's light differ from its disk average.

Transit method

The transit method detects exoplanets by watching a star's brightness for periodic dips when a planet crosses it; HD 209458 b was the first transit observed, in 1999.

Transit photometry

Transit photometry detects exoplanets by measuring the periodic dip in a star's brightness when a planet crosses its disk, and has found over 4000 known exoplanets.

Transit spectroscopy

Transit spectroscopy is an astronomical method that measures a transiting exoplanet's transit depth at each wavelength to determine the composition and structure of its atmosphere.

Transit timing variations

Transit timing variations (TTVs) are deviations of an exoplanet's transit times from a constant orbital period, caused by other planets' gravity, revealing non-transiting planets and measuring masses.

Transit-timing variation

Transit-timing variation (TTV) is an exoplanet detection method that measures deviations from a linear ephemeris in transit times, caused by gravitational interactions between planets, strongest near mean-motion resonance.

TRAPUM

TRAPUM (TRAnsients and PUlsars with MeerKAT) is a survey project on the MeerKAT telescope in South Africa that searches for pulsars and fast radio transients.

Trigonometric parallax

Trigonometric Parallax is an astrometric method measuring a star's angular shift as Earth orbits, forming the first step of the cosmic distance ladder.

Triple quasar

A triple quasar is a system of three quasars, each powered by a supermassive black hole, observed close together and physically associated rather than aligned by chance.

Tully-Fisher relation

The Tully-Fisher relation, proposed by R. Brent Tully and J. Richard Fisher in 1977, links spiral galaxy luminosity to rotation velocity, making it a widely used extragalactic distance indicator.

Two Micron All-Sky Survey

The Two Micron All-Sky Survey (2MASS) was a ground-based near-infrared survey that imaged the entire sky from 1997 to 2001, producing catalogs of over 470 million objects.

UBV photometric system

The UBV photometric system, also called the Johnson or Johnson-Morgan system, is a broad-band photometric system with three filters: U (ultraviolet), B (blue), and V (visual).