Physical world and mathematics

Red Forest

The Red Forest, also known as the Wormwood Forest, is a pine woodland near Chernobyl's Reactor 4 whose Scots pines died from radiation after the 1986 accident.

Red giant

A red giant, or red giant star, is a late stage of a star's life, in which the star swells to as much as 100 times its original size.

Red giant branch

The red giant branch (RGB) is the phase of stellar evolution in which stars of roughly 0.8 to 8 solar masses burn hydrogen in a shell around an inert helium core.

Oct 21, 2026

Red Hill-Quemado volcanic field (Quemado volcanic field): basaltic monogenetic field in Catron County, western New Mexico, on the Jemez lineament, with 40+ cinder cones and maars active from about 8 Ma to the early Holocene, including Zuni Salt Lake maar.

Red phosphorus

Red phosphorus is a dark red, polymeric allotrope of phosphorus, far less reactive and nontoxic than white phosphorus, used on safety-match striking surfaces and as a flame retardant.

Red rain in Kerala

The red rain in Kerala, or Kerala red rain phenomenon, was a series of red rain events that began in Kerala, India, on 25 July 2001.

Red Rectangle Nebula

The Red Rectangle Nebula is a proto-planetary nebula surrounding the star HD 44179, about 2,300 light-years away in the constellation Monoceros, named for its rectangular shape and red color in early images.

Red Sea

The Red Sea is a long, narrow ocean basin between northeastern Africa and the Arabian Peninsula, among the world's warmest and saltiest seas and a critical global shipping route.

Red sky at morning

"Red sky at morning" is the warning half of the weather proverb "Red sky at night, sailors' delight", a forecasting rule of thumb with a real basis.

Red soil

Red soil is soil colored red or brownish red by iron oxides, chiefly hematite, that forms in hot, humid climates and supports much tropical agriculture.

Red supergiant

A red supergiant is a large, cool, luminous star formed when a massive star leaves the main sequence, and the progenitor of Type II supernovae.

Red supergiant pre-supernova variability

Red supergiant pre-supernova variability is the brightening or dimming of a red supergiant in the months before its supernova, first confirmed for SN 2020tlf 130 days before explosion.

Redeposition

Redeposition in fusion devices is the return of sputtered plasma-facing material to nearby surfaces after ionization in the edge plasma, differing between high-Z materials like tungsten and low-Z ones.

Redescending M-estimator

A redescending M-estimator is a robust statistical estimator whose influence function rises near the data's center and falls to zero for large residuals, completely rejecting extreme outliers instead of merely down-weighting them.

Redfield ratio

The Redfield ratio is the constant atomic ratio of carbon, nitrogen, and phosphorus in marine plankton, 106C : 16N : 1P, named for Alfred C. Redfield.

Redlich–Kwong equation of state

The Redlich–Kwong equation of state is a two-parameter cubic equation of state for real gases, proposed by Otto Redlich and Joseph N. Kwong in 1949 to improve on the van der Waals equation.

RedMaPPer

RedMaPPer (red-sequence Matched-filter Probabilistic Percolation) is a photometric galaxy-cluster finding algorithm introduced by Eli Rykoff and Eduardo Rozo in 2014, whose catalogs of red-sequence clusters are widely used for cluster cosmology.

Redox

Redox (reduction–oxidation) is a chemical reaction in which electrons are transferred: the species losing electrons is oxidized, and the receiver is reduced; the two changes always occur together.

Redox non-innocent ligands in electrocatalysis

Redox non-innocent ligands are ligands in metal complexes that share electrons with the metal center, acting as electron and proton reservoirs for multielectron electrocatalytic reactions.

Redox titration

A redox titration is a titration method in which an analyte is measured through an oxidation–reduction reaction with a titrant of known concentration, calculated from the volume consumed at the endpoint.

Redox-active esters

Redox-active esters (RAEs), most commonly N-hydroxyphthalimide (NHPI) esters, are carboxylic acid derivatives that fragment on single-electron reduction to give carbon radicals, letting chemists use abundant carboxylic acids in nickel-catalyzed cross-coupling.