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Hausdorff dimension
The Hausdorff dimension, also called the Hausdorff-Besicovitch dimension, is a possibly fractional measure of a set's size, introduced by Felix Hausdorff in 1918; the middle-third Cantor set has dimension log 2 / log 3.
Hausdorff distance
The Hausdorff distance, introduced by Felix Hausdorff in 1914, is a metric on compact subsets of a metric space, used in medical image segmentation and comparing point clouds.
Hausdorff maximal principle
The Hausdorff maximal principle, also called the Hausdorff maximality theorem, states that every chain in a partially ordered set is contained in a maximal chain, and is equivalent to Zorn's lemma.
Hausdorff measure
The Hausdorff measure is a family of measures introduced by Felix Hausdorff in 1918 that assigns sizes to sets of any dimension, including fractals, and extends the Lebesgue measures of length, area, and volume.
Hausdorff space
A Hausdorff space, also called a T2 space or separated space, is a topological space in which any two distinct points can be separated by disjoint neighborhoods.
Hauser–Feshbach model
The Hauser–Feshbach model is a statistical theory of compound-nuclear reactions that conserves angular momentum and parity, used in codes like TALYS from kilovolts to tens of MeV.
Hausman test
The Hausman test is a statistical specification test in econometrics, introduced by J. A. Hausman in 1978, that compares two estimators and rejects the null when they diverge.
Hausmannite
Hausmannite is a brown-black manganese oxide mineral with the formula Mn²⁺Mn³⁺₂O₄, a tetragonally distorted spinel found in hydrothermal veins and metamorphosed manganese deposits.
Hausner ratio
The Hausner ratio is a dimensionless index of powder flowability, defined as a powder's tapped bulk density divided by its untapped bulk density; values near 1 indicate free flow.
Haute-Provence Observatory
The Haute-Provence Observatory (Observatoire de Haute-Provence, OHP) is a French astronomy and atmospheric science site near Saint-Michel-l'Observatoire, where 51 Pegasi b, the first exoplanet around a Sun-like star, was discovered in 1995.
Hauterivian
The Hauterivian is a stage of the Early Cretaceous, spanning about 132.6 to 125.77 million years ago between the Valanginian and Barremian, named after Hauterive, Switzerland.
Havala Pye
Havala Olson Taylor Pye is an American research physical scientist at the EPA in Research Triangle Park, North Carolina, who leads development of the CRACMM chemical mechanism.
Haversine formula
The haversine formula, also known as the haversine distance, computes the great-circle distance between two points on a sphere from their latitudes and longitudes, using the haversine trigonometric function.
Havok Physics
Havok Physics is a commercial real-time rigid-body physics engine developed by Dublin company Havok, founded in 1998, owned by Microsoft since 2015, and used in over 600 games.
Hawaii Ocean Time-series
The Hawaii Ocean Time-series (HOT) is a quasi-monthly oceanographic program that has measured hydrography, chemistry, and biology at Station ALOHA, 100 km north of Oahu, since October 1988.
Hawaiian–Emperor seamount chain
The Hawaiian–Emperor seamount chain, also called the Hawaiian Ridge Emperor Seamounts, is a mostly submarine line of over 100 Pacific volcanoes spanning about 6,000 km.
HAWC
HAWC (High-Altitude Water Cherenkov Observatory) is a ground-based gamma-ray and cosmic-ray observatory at 4,100 meters on the Sierra Negra volcano in Puebla, Mexico, completed in 2015 as successor to Milagro.
Hawk Fire
The Hawk Fire was a wind-driven wildfire that burned on Peavine Peak northwest of Reno, Nevada, in August 2026, destroying 47 homes and prompting evacuations of roughly 90,000 people.
Hawkes process
The Hawkes process is a self-exciting point process introduced by Alan G. Hawkes in 1971, in which each event temporarily raises the probability of further arrivals.
Hawking area theorem
The Hawking area theorem is a 1971 result by Stephen Hawking stating that the total event horizon area of classical black holes never decreases, paralleling the second law of thermodynamics.
Hawking mass
The Hawking mass is a quasilocal mass in general relativity that estimates the gravitational energy enclosed by a closed two-surface, introduced by Stephen Hawking in 1968.
Hawking radiation
Hawking radiation is the thermal emission predicted by Stephen Hawking in 1974 at a black hole's event horizon, making black holes slowly lose mass and evaporate.
Hawking–Page transition
The Hawking–Page transition is a first-order phase transition between thermal radiation and a large black hole in anti-de Sitter space, found by Hawking and Page in 1983.
Hawking's time traveller party
Hawking's time traveler party was a reception Stephen Hawking held at noon on 28 June 2009 at Gonville & Caius College, Cambridge, with invitations sent only afterward; nobody came.
Haydn H. Murray
Haydn H. Murray, also known as Haydn Herbert Murray, was an American clay mineralogist, a Georgia Kaolin executive who built Indiana University's applied clay science program.
Haydn Herbert Murray
Haydn Herbert Murray (1924–2015) was an American clay mineralogist and leading expert on kaolin, who directed research at Georgia Kaolin before chairing geology at Indiana University.
Haynesville Shale
The Haynesville Shale is an Upper Jurassic shale gas play more than 10,000 feet beneath northwestern Louisiana, eastern Texas, and southwestern Arkansas, producing natural gas at scale since 2008.
HAYSTAC
HAYSTAC (Haloscope at Yale Sensitive To Axion CDM) is a tunable microwave cavity experiment at Yale University searching for axion dark matter, and the first to use a squeezed-state receiver.
Hayward Fault Zone
The Hayward Fault is a major strike-slip branch of the San Andreas fault system running through Berkeley, Oakland, Hayward, and Fremont, with large earthquakes every 100 to 200 years.
Hayward metric
The Hayward metric is a regular black-hole spacetime in general relativity, introduced by Sean A. Hayward in 2006, replacing the central singularity with a finite de Sitter-like core.