Cosmology and observation

Deep learning in gravitational-wave astronomy

Deep learning in gravitational-wave astronomy applies neural networks, especially CNNs, to detect and localize gravitational waves and classify glitches, complementing matched filtering in LIGO, Virgo, and KAGRA searches.

DENIS

DENIS (DEep Near-Infrared Survey of the Southern Sky) was a European astronomical survey that imaged the southern sky in one optical and two near-infrared bands from La Silla, Chile.

Density parameter

The density parameter, written Ω (Omega), is the ratio of the actual mean density of the universe or a component to the critical density, and the components sum to 1.

DESI Legacy Surveys

The DESI Legacy Surveys are three public optical imaging surveys, combined with WISE infrared data, that produced the target catalogs for the Dark Energy Spectroscopic Instrument.

DESI survey

The DESI survey is a five-year spectroscopic redshift survey of tens of millions of galaxies and quasars, run by the Dark Energy Spectroscopic Instrument at Kitt Peak.

Differential imaging

Differential imaging is a family of high-contrast astronomical techniques that builds a model of a star's light from reference images and subtracts it, revealing faint exoplanets and disks near the star.

Sep 29, 2026

Direct imaging (astronomy)

Direct imaging of exoplanets is an observational astronomy technique that records light from planets resolved from their host star, first achieving success with 2M1207b in 2004.

Discoveries of exoplanets

The discoveries of exoplanets, planets orbiting stars other than the Sun, began with confirmed detections in 1992 and now total more than 6,400 confirmed worlds, found mainly by transit and radial-velocity methods.

Discovery of cosmic microwave background radiation

The discovery of the cosmic microwave background radiation was made by Arno Penzias and Robert Wilson at Bell Labs in Holmdel, New Jersey, in 1964–65.

Distance modulus

The distance modulus is the difference between an astronomical object's apparent and absolute magnitude, μ = m − M, which provides a direct measure of its distance.

Distance redshift relation

The distance redshift relation links an object's redshift, the stretching of its light by cosmic expansion, to its distance; measured with supernovae, it revealed the accelerating expansion driven by dark energy.

Doppler peak

The Doppler peak, also called the acoustic or Sakharov peak, is a prominent peak in the cosmic microwave background's power spectrum, produced by acoustic oscillations of the early photon-baryon plasma.

Sep 29, 2026

Doppler spectroscopy

Doppler spectroscopy, also called the radial-velocity method, measures wavelength shifts of a moving object's light to find its velocity, and detected the first exoplanet around a Sun-like star in 1995.

Drake equation

The Drake equation, also called the Green Bank equation, is a 1961 formula by Frank Drake estimating the number of radio-transmitting civilizations in the Milky Way.

Sep 29, 2026

Drizzle (astronomy)

Drizzle is an image-combination algorithm that resamples and combines dithered telescope exposures onto a finer pixel grid, developed for undersampled Hubble cameras and now standard in HST and JWST pipelines.

Dual quasar

A dual quasar is a pair of quasars powered by two different supermassive black holes, shining simultaneously in a single merging galaxy system, typically separated by kiloparsecs.

Dusty torus

A dusty torus is an optically thick distribution of dust around the accretion disk and supermassive black hole of an active galactic nucleus, re-emitting absorbed radiation in the infrared.

E-mode polarization

E-mode polarization is the curl-free (gradient-like) component of the cosmic microwave background's linear polarization, produced by Thomson scattering and first detected by DASI in 2002.

E1821+643

E1821+643, also cataloged as H1821+643, is a luminous radio-quiet quasar about 3.4 billion light-years away in Draco, hosted by a giant elliptical galaxy at the center of a rich cluster.

Early dark energy

Early dark energy (EDE) is a proposed dark-energy component that briefly became significant in the early universe before diluting away, proposed to resolve the Hubble tension.

EBEX

EBEX, the E and B Experiment, was a balloon-borne polarimeter that measured cosmic microwave background polarization, flying near the South Pole for about 25 days in 2012-13.

eBOSS

eBOSS, the Extended Baryon Oscillation Spectroscopic Survey, mapped the large-scale structure of the Universe from 2014 to 2019 on the Sloan telescope, measuring cosmic expansion through baryon acoustic oscillations.

Eclipse

An eclipse occurs when the Sun, Moon, and Earth line up: a solar eclipse at new moon, and a lunar eclipse when the full Moon enters Earth's shadow.

Eclipse mapping

Eclipse mapping is an exoplanet astronomy technique that uses the changing shape of a secondary eclipse to reconstruct a two-dimensional map of a planet's dayside brightness or temperature.

Eddington experiment

The Eddington experiment, also called the Dyson-Eddington-Davidson experiment, was the 1919 solar eclipse test of Einstein's general relativity by two British expeditions whose results made Einstein world-famous.

EDGES

EDGES, a radio astronomy experiment by Arizona State University and MIT, claimed in 2018 the first detection of the global 21-centimeter signal from Cosmic Dawn.

Effective field theory of large-scale structure

The effective field theory of large-scale structure (EFTofLSS) is a cosmological framework that predicts matter and galaxy clustering by treating dark matter as an effective fluid.

Electromagnetic follow-up of gravitational-wave events

Electromagnetic follow-up of gravitational-wave events is the search with optical, radio, X-ray, and other telescopes for light from gravitational-wave sources, most successfully for GW170817 in 2017.

Entropy of the universe

The entropy of the universe is the total thermodynamic entropy in the observable universe, estimated at about 10^104 k, with supermassive black holes contributing almost all of it.