42,772 articles
Hazard and operability study
A hazard and operability study (HAZOP), also known as Hazard and Operability Analysis, is a structured team technique that uses guide words such as No, More, and Reverse to identify process deviations.
Hazard ratio
The hazard ratio (HR) is a measure in survival analysis that compares the instantaneous event rates of two groups, most often estimated with the Cox proportional-hazards model, and is not a risk ratio.
Haze
Haze is a suspension of extremely small dry particles, such as dust, smoke, or pollution, that reduces visibility and gives the air an opalescent appearance.
Hazen–Williams equation
The Hazen–Williams equation, or Hazen–Williams formula, is an empirical formula estimating water friction loss in pipes, published by Allen Hazen and G. S. Williams in 1905.
HBV model
The HBV model (Hydrologiska Byråns Vattenbalansavdelning) is a conceptual rainfall-runoff model developed by Sten Bergström at the Swedish Meteorological and Hydrological Institute in 1972, converting precipitation and temperature into river discharge.
HD 10069b
HD 10069b, also known as WASP-18b, is one of the most massive known hot Jupiters, a gas giant orbiting the star HD 10069 in Phoenix every 0.94 days, discovered in 2009.
HD 10307
HD 10307, also HR 483, is a Sun-like G-type star about 41 light-years away in Andromeda with a red dwarf companion orbiting every 19.5 years.
HD 103095
HD 103095, better known as Groombridge 1830, is a metal-poor yellow-orange subdwarf star in Ursa Major about 30 light-years away, cataloged by Stephen Groombridge in the early nineteenth century.
HD 106516
HD 106516, also cataloged as HR 4657, is an F-type spectroscopic binary in Virgo about 22 parsecs away, a rare blue straggler of the Milky Way's thick disk.
HD 10780
HD 10780, also called V987 Cas, is a nearby K-type main-sequence star in Cassiopeia and a BY Draconis variable, visible near the naked-eye limit at magnitude 5.6.
HD 109573
HD 109573, also cataloged as HR 4796A, is a young A0V star about 237 light-years away in Centaurus, known for one of the brightest, sharpest debris rings known.
HD 122563
HD 122563 is an extremely metal-poor red giant star in the halo of the Milky Way, identified in 1963 and the brightest known metal-poor halo giant at magnitude 6.2.
HD 131977
HD 131977, also GJ 570 A or KX Librae, is a K-type star in Libra about 19 light-years away, the primary of the quadruple Gliese 570 system.
HD 135344B
HD 135344B, also cataloged as SAO 206462, is a young star about 440 light-years away in Lupus with a protoplanetary disk known for two spiral arms.
HD 140283
HD 140283, known as the Methuselah star, is an extremely metal-poor Population II subgiant in the constellation Libra, about 190 light-years away, a benchmark for testing stellar ages against the Universe's age.
HD 141569
HD 141569 is a young triple star system about 320 light-years away in Libra, surrounded by a structured disk caught between protoplanetary and debris stages.
HD 142527
HD 142527 is a young Herbig Ae/Be star of type F6 in the constellation Lupus, about 450 light-years away, with a widely studied protoplanetary disk.
HD 148937
HD 148937 is a binary of two massive O-type stars in Norma about 3800 light-years away, where a 2024 study showed the magnetic star formed in a stellar merger.
HD 149026b
HD 149026b, officially named Smertrios, is a hot Saturn-mass exoplanet orbiting the metal-rich subgiant HD 149026 every 2.88 days. Discovered in 2005, it is the most metal-rich giant planet known.
HD 15082b
HD 15082b, also designated WASP-33b, is an ultra-hot Jupiter exoplanet discovered in 2010 by the SuperWASP survey, the first planet found transiting an A-type star.
HD 163296
HD 163296 is a young Herbig Ae star about 330 light-years away in Sagittarius, roughly twice the Sun's mass and 4 million years old, with a planet-forming disk.
HD 184738
HD 184738, also known as Campbell's star or Campbell's hydrogen star, is a small planetary nebula in Cygnus discovered in 1893, whose central star has a rare Wolf-Rayet-like spectrum.
HD 190918
HD 190918, also cataloged as WR 133 and V1676 Cyg, is a Wolf-Rayet binary in Cygnus where a WN5o star orbits an O9 supergiant every 112.8 days.
HD 191765
HD 191765, also known as WR 134, is a WN6 Wolf-Rayet star in Cygnus, one of three stars in which Wolf and Rayet discovered the class in 1867.
HD 193576
HD 193576, also cataloged as V444 Cygni and WR 139, is an eclipsing binary star in Cygnus about 6,200 light years away, made up of a Wolf–Rayet star and an O-type companion.
HD 193793
HD 193793, better known as WR 140, is a massive Wolf-Rayet and O5 binary star in Cygnus, the prototype of colliding-wind binaries that make dust every 7.9 years.
HD 19445
HD 19445 is a metal-poor F-type subdwarf in Perseus, an ancient Population II halo star about 40 parsecs away, one of the first stars shown to be metal-deficient.
HD 199579
HD 199579 is a spectroscopic binary star in the constellation Cygnus about 870 light years away, consisting of an O6.5V primary and a B-type companion in a 48.5-day orbit.
HD 200775
HD 200775, also cataloged as MWC 361, is a young, massive Herbig Be star in Cepheus that illuminates the reflection nebula NGC 7023, the Iris Nebula.
HD 201891
HD 201891, also cataloged as HIP 104659, is a metal-poor G-type dwarf star in Equuleus about 33.5 parsecs from the Sun, roughly 10 billion years old and a long-serving spectroscopic standard.