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Galaxy group
A galaxy group is the smallest collection of galaxies bound by mutual gravity, typically a few to a few dozen members; the Milky Way's Local Group is one.
Galaxy luminosity function
The galaxy luminosity function gives the number of galaxies per unit volume at each luminosity, described by the Schechter function proposed in 1976 and used to test galaxy-formation models.
Galaxy merger
A galaxy merger is the collision and coalescence of two or more galaxies, driving the transformation of disc galaxies into massive ellipticals and triggering starbursts.
Galaxy morphological classification
Galaxy morphological classification, also called galaxy morphology or galaxy types, sorts galaxies into elliptical, spiral, lenticular, and irregular classes by their visual appearance, using the scheme Edwin Hubble proposed in 1926.
Galaxy rotation curve
A galaxy rotation curve plots the orbital speed of stars and gas against distance from the galactic center; flat outer curves are key evidence for dark matter.
Galaxy spectroscopy
Galaxy spectroscopy is the technique of dispersing the light of whole galaxies into spectra to measure redshifts, internal velocities, and the physical properties of their stars and gas.
Galaxy Zoo
Galaxy Zoo is an online citizen science project where volunteers classify galaxy shapes, launched in July 2007 with a million Sloan Digital Sky Survey galaxies.
Galaxy–halo connection
The galaxy–halo connection is the statistical relationship between galaxies and the dark matter halos they form in, inferred because dark matter is not directly observable.
Gale warning
A gale warning is a marine weather warning issued for sustained winds, or frequent gusts, of 34 to 47 knots over water, excluding winds from tropical cyclones.
Galen D. Stucky
Galen D. Stucky (G. D. Stucky) is an American inorganic and materials chemist at UC Santa Barbara, known for synthesizing mesoporous silicas such as SBA-15.
Galena
Galena, also known as lead glance or blue lead, is lead sulfide, the world's most important ore of lead, used by humans for thousands of years.
Galerkin method
The Galerkin method, also known in Russia as the Bubnov–Galerkin method, reduces differential equations to finite algebraic systems and forms the backbone of the finite element method; Boris Galerkin formulated it in 1915.
Galilean group
The Galilean group, also called the Galilei group, is the ten-parameter Lie group of transformations between inertial reference frames in Newtonian mechanics, encoding rotations, translations, boosts, and time shifts.
Galilean invariance
Galilean invariance, also called Galilean relativity, is the principle that Newton's laws take the same form in every inertial frame, connected by the Galilean transformation.
Galilean moons
The Galilean moons, also called the Galilean satellites or Medicea Sidera, are Jupiter's four largest moons, Io, Europa, Ganymede, and Callisto, discovered by Galileo Galilei in January 1610 and believed to hold subsurface oceans.
Galilean transformation
The Galilean transformation, also called the Galilean boost, is the classical mechanics coordinate transformation relating inertial frames moving at constant relative velocity, with time universal, and it fails for light, requiring Lorentz transformations.
Galileo affair
The Galileo affair, also called the prosecution of Galileo, was the Roman Catholic Church's dispute with Galileo over Copernicanism, ending in his 1633 condemnation and abjuration.
Galileo Galilei
Galileo Galilei was a Pisa-born Italian astronomer, physicist, and mathematician who discovered Jupiter's moons, pioneered mathematical physics, and was convicted of heresy by the Roman Inquisition in 1633.
Galileo thermometer
The Galileo thermometer, also called a Galilean or density thermometer, is a sealed glass cylinder whose calibrated floating bulbs indicate temperature; it is decorative, not precise.
Galileo's Leaning Tower of Pisa experiment
Galileo's Leaning Tower of Pisa experiment is the textbook story that Galileo dropped two cannonballs from the tower around 1590 to show unequal weights fall at the same rate.
Gall–Peters projection
The Gall–Peters projection, also known as the Peters projection, is a cylindrical equal-area map projection that preserves area exactly while distorting shapes, presented by James Gall in 1855.
Gallanediyl
Gallanediyl is a monovalent gallium compound of the type RGa, the gallium analog of a carbene, with a lone pair and vacant p orbital on gallium.
Gallic acid
Gallic acid, or 3,4,5-trihydroxybenzoic acid, is a naturally occurring phenolic plant acid known as the building block of hydrolyzable tannins and a component of iron gall ink.
Galling
Galling is a severe form of adhesive wear in which plastic deformation and fracture roughen sliding surfaces and transfer material, commonly seizing stainless steel fasteners and valve seats.
Gallium
Gallium is a soft, silvery-white metal, atomic number 31, that melts in a warm hand; its compounds GaAs and GaN are essential to LEDs and electronics.
Gallium anomaly
The gallium anomaly is an unexplained deficit of about 20 percent in electron neutrino capture on gallium, seen in SAGE, GALLEX/GNO calibration experiments and the BEST experiment.
Gallium arsenide spin qubits
Gallium arsenide spin qubits are quantum bits encoded in electron spins in GaAs quantum dots, first demonstrated in 2005 and still used for experiments despite nuclear-spin decoherence limiting coherence to tens of nanoseconds.
Gallium gadolinium garnet
Gallium gadolinium garnet (GGG), or gadolinium gallium garnet, is a synthetic oxide crystal used as the standard substrate for magnetic garnet films and studied as a frustrated magnet.
Gallium nitride
Gallium nitride, also called gallium mononitride (GaN), is a wide-bandgap compound semiconductor of gallium and nitrogen whose efficient blue LED earned the 2014 Nobel Prize in Physics.
Gallium phosphide
Gallium phosphide is an indirect-bandgap III-V semiconductor, transparent and orange in appearance, that drove commercial LED production in the early 1970s and now serves as an optical substrate.