• Haber, Fritz

  • [person - physical & chemical properties, thermodynamics] German chemist born in Breslau (1868-1934). Haber began his career in chemistry with investigations on the decomposition and combustion of hydrocarbons. In 1898, he published his textbook Electrochemistry, and followed this with increasing investigations of electrochemical phenomena. Among these experiments, he researched the electrolysis of solid salts, and energy loss by steam engines. In 1918, Haber was awarded a Nobel Prize in Chemistry for his research on nitrogen fixation from the air, a key component in the development of nitrogen fertilizers.

  • habitat

  • [noun - organisms, biodiversity & ecological relationships, bioregions, biomes & ecosystems] The place or type of environment where a wild plant, animal, or other organism naturally lives or grows.

  • Hadley cell

  • [noun - atmospheric science, weather & climate] The primary circulation cell in Earth’s atmosphere. Warm, wet air rises in the Intertropical Convergence Zone, causing abundant precipitation as it cools; the air then flows north and south and cools, sinking as a cold, dry air mass at 30° N and S, producing a band of deserts.

  • Hadley, George

  • [person - atmospheric science] (1685-1768) English natural philosopher who took up physics after giving up practicing law. Hadley is best known for describing circulation in the atmosphere between the equator and 30° N and S, in what is now known as the Hadley cell. His explanation was the first to invoke the idea that the rotation of the Earth causes an apparent deflection of the winds, known today as the Coriolis effect. Hadley was a member of the Royal Society of London and in charge of compiling the society’s observations from its network of meteorological observers.

  • Haldane, J.B.S.

  • [person - genetics & inheritance, medicine] (1892–1964) John Burdon Sanderson Haldane (known most frequently as JBS Haldane) contributed to several areas of science. He connected Darwin’s theory of natural selection with Mendel’s laws of genetics, proposing the first modern hypothesis on the origin of life. He also explored decompression sickness occurring in people returning to sea level after working underwater on bridges. In his era, Haldane was well known throughout British society as an advocate and explainer of science.

  • half-life

  • [noun - chemical reactions, organic & biochemistry] The time required for half of the original amount of a substance to undergo a process. For example, the time required for half of the atoms of a radioactive substance to undergo decay; or the time required for half of a ingested substance to be excreted from the body.

  • Halley, Edmund

  • [person - cosmology, planetary science] English astronomer born in Derbyshire (1656-1742). He observed transits of Mars and Venus to determine the distance from the Earth to the Sun, and accurately predicted the return of a comet, now named after him.

  • haplotype

  • [noun - genetics & inheritance] Genetic sequences that we inherit from only one parent. Haplotypes include sequences from mitochondrial DNA (mtDNA) and the non-homologous portion of the Y chromosome. They differ from autosomal genes, which are shuffled due to recombination of segments of DNA that transfer, or crossover, between homologous chromosomes during meiosis.

  • Hardy-Weinberg Equilibrium

  • [noun - genetics & inheritance] Principle in population biology that the frequencies of alleles and genotypes remain constant from generation to generation in the absence of evolutionary forces. It was proposed independently and in slightly different forms by three researchers: William Castle (1903, US), Wilhelm Weinberg (1908, Germany), and Godfrey Harold Hardy (1908, UK).

  • Hau, Lene

  • [person - light & optics] Danish physicist born in Vejle (1959-). Her most famous work consisted of experiments in slowing down light. In 1999, she and several colleagues succeeded in slowing light to 17 m/s, and in 2001, they managed to very briefly stop a light beam. In 2007, she and her research team transformed light into matter and back into light using Bose-Einstein condensates.

  • Hawking, Stephen

  • [person - cosmology] British cosmologist and theoretical physicist, born in Oxford (1942-). His most important contributions to science have been his study of quantum gravity and black holes. He also authored the extremely popular A Brief History of Time, which spent 237 weeks on the British Sunday Times best-seller list. Hawking suffers from amyotrophic lateral sclerosis (ALS), a degenerative motor neural disease also known as Lou Gehrig's disease, which was diagnosed during his graduate studies. He is confined to a wheelchair and speaks through a voice-box. As part of an ongoing effort to popularize science and space-travel, Hawking went on a sub-orbital flight, during which he became the first quadriplegic to experience antigravity.

  • heat

  • [noun - energy, energy, thermodynamics] A measure of the total internal energy of a substance that can be increased or decreased when objects with different temperatures are placed into contact. Heat is a process, not a property of a material.

  • Heisenberg Uncertainty Principle

  • [noun - laws & theories, atoms & subatomic particles, modern physics] A mathematical assertion in quantum mechanics, that states that both the position and momentum of a particle cannot be simultaneously, accurately known. As the certainty of one quantity increases, the certainty of the other decreases.

  • Heisenberg, Werner

  • [person - atoms & subatomic particles, modern physics] German physicist instrumental in the development of quantum mechanics for which he won the Nobel Prize in 1932 in physics for, "the creation of quantum mechanics." Known particularly for the Heisenberg Uncertainty Principle.

  • heliocentric

  • [adjective - planetary science] Having or representing the sun as a center, as in the heliocentric concept of the universe. Compare to geocentric.

  • hemagglutination

  • [noun - biomolecules, medicine] The clumping together of red blood cells as a result of antibodies that bind to specific blood group antigens. Hemagglutination is method to determine blood type.

  • hematocrit

  • [noun - anatomy & physiology, medicine] The portion of blood made up of red blood cells, measured as the volume percentage of the whole blood.

  • Heraclitus

  • [person - scientific concepts] A Greek philosopher from Ephesus (535-475 BCE). His philosophy consisted of a belief that everything is in a constant state of flux, and that opposites are not only necessary in life because they provide balance but are also, in fact, identical.

  • heredity

  • [noun - evolution & adaptation] The passing of genetic traits from parent to offspring.

  • Herschel, John

  • [person - stellar and galactic astronomy] Scottish astronomer born in Slough (1792-1871). Herschel studied double star systems, made a comprehensive map of the celestial Southern hemisphere, and was a pioneer and strong proponent of the use of photography in astronomy, now a staple of astronomical research. His book Outlines of Astronomy was a standard textbook for decades after its publication, and the modern New General Catalog (the best-known catalogue of deep sky objects in amateur astronomy) is derived largely from his General Catalogue of Nebulae and Clusters.

  • Herschel, William

  • [person - planetary science, stellar and galactic astronomy] English astronomer and composer born in Hanover, Germany (1738-1822). Herschel worked closely with his sister, Caroline. Their most important contribution was the discovery, in 1781, of the planet Uranus. They also discovered two moons of Uranus in 1787, and two of Saturn's moons. William Herschel's work on double stars showed that gravity acts outside of the solar system. He also studied sunspots and their connection to weather.

  • Hershey, Alfred

  • [person - anatomy & physiology, genetics & inheritance] (December 4, 1908 - May 22, 1997) An American bacteriologist and geneticist. His most famous contribution to science was the Hershey-Chase blender experiment, which he and Martha Chase performed, the results of which supported the idea that genetic material is made up of DNA, not protein. In 1962, Hershey was awarded the Nobel Prize in Physiology or Medicine (shared with two other researchers) for work on the genetic structure and replication of viruses.

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    • DNA I
  • Hess, Harry

  • [person - oceanography, seismology & plate tectonics] American marine geologist born in New York, New York (1906-1969). Hess was key scientist in the establishment of the theory of plate tectonics in the early 1960s. From observations he made of the seafloor while serving in the US Navy during World War II, he developed the idea of seafloor spreading, which he published in 1962 in the paper "History of Ocean Basins."

  • heterogeneous mixture

  • [noun - materials science] A mixture of two or more substances that can be easily separated by common physical means (i.e., settling, filtration, etc.). A mixture in which the components can be visibly distinguished, for example, oil and water. Compare to homogeneous mixture.

  • heterozygous

  • [adjective - genetics & inheritance] Having two different alleles for a given gene.

  • Higgs boson

  • [noun - atoms & subatomic particles, atoms & subatomic particles, modern physics] An elementary particle in the standard model of particle physics that gives other particles mass. Proposed in 1964 by Peter Higgs and François Englert in separate papers, and discovered in CERN’s Large Hadron Collider in 2012, the degree to which a particle interacts with Higgs bosons that make up the Higgs Field, determines its relative mass. Higgs and Englert were awarded the Nobel Prize for Physics in 2013 for their work.

  • hindcast

  • [noun - weather & climate, statistics] a determination of likely past conditions based on mathematical and statistical calculations. Hindcasts can be compared to forecasts, which is a statistical prediction of probable future conditions

  • Hipparchus

  • [person - astrophysics] Greek astronomer, mathematician, and geographer born in Nicaea (ca. 190-120 BCE). Hipparchus made the oldest surviving quantitative and accurate models for the motion of the Sun and Moon. He also developed a method for accurately predicting solar eclipses and compiled the first comprehensive star catalogue of the western celestial hemisphere.

  • homeothermic

  • [adjective - anatomy & physiology, organisms] Of, or pertaining to, the maintenance of a uniform temperature regardless of the temperature of the surroundings. In biology, synonymous with warm-blooded.

  • hominid

  • [noun - evolution & adaptation, taxonomy & systematics] A member of the Hominidae family of erect bipedal primates, which includes modern humans along with our extinct ancestors and related forms.

  • homogeneous mixture

  • [noun - physical & chemical properties] A mixture of two or more substances that cannot be easily separated by common physical means (i.e., settling, filtration, etc.). A mixture with no visible separation between its components, for example, salt and water. Compare to heterogeneous mixture.

  • homozygous

  • [adjective - genetics & inheritance] Having two identical alleles for a given gene.

  • Hooke, Robert

  • [person - cells, equations] An English physicist, born on the Isle of Wight (1635-1703). Hooke's studies were extremely diverse, encompassing biology, geology, physics, chemistry, and astronomy. He was also an accomplished inventor: He designed the universal joint, the iris diaphragm, a prototype of a respirator, and the balance spring. In 1662, he became the first Curator of Experiments for the Royal Society of London. Hooke discovered the theory for combustion and devised an equation for elasticity, which is now known as Hooke's Law. He also made important contributions in biology by describing and naming cells, which he observed with a compound microscope that he designed.

  • hormone

  • [noun - biomolecules, medicine] A chemical compound that is secreted from a gland directly into the blood that acts as a chemical messenger to tissues and organs.

  • horticulture

  • [noun - organisms, organisms] The science and art of cultivating plants.

  • hot spot

  • [noun - seismology & plate tectonics] A fixed plume of hot magma which rises through the mantle and creates volcanoes on the Earth’s surface. The Hawaiian Island chain is an example of a hot spot. Because the plumes are fixed, the hot spots record past plate motions.

  • Hubble constant

  • [noun - planetary science, stellar and galactic astronomy] (H0) a numerical value of the expansion factor of the universe. In 1929, Hubble identified this value as 500 km/sec/Mpc (kilometers per second per megaparsec). Today, this value has been refined (as a result of extensive research) to range from 45-90 km/sec/Mpc.

  • Hubble, Edwin Powell

  • [person - planetary science, stellar and galactic astronomy] Astronomer, born in Missouri, United States (1889-1953). Author of The Observational Approach to Cosmology and The Realm of the Nebulae (1935). Hubble was the first individual to demonstrate the existence of galaxies outside of our own. He also used Vesto Slipher's redshift data to show that the degree of redshift increases with distance, thus providing evidence that the universe is expanding. He discovered the asteroid 1373 Cincinnati.

  • Hudson, Henry

  • [person - weather & climate] (1560?-1611?) An English sea explorer and navigator in the early 17th century. While searching for the Northwest Passage to India, he explored and mapped the region around what is now New York City, and named Hudson Bay and Hudson River after himself. Hudson made four voyages in search of alternate routes to India, in 1607, 1608, 1609, and 1610. On his last voyage, his ship became trapped in ice in James Bay in the fall of 1610, and had to winter over. Hudson wanted to continue exploring when the spring thaw freed the boat, but his crew mutinied. Hudson, his son, and six others were cast adrift in a small, open boat, never to be heard from again.

  • Human Genome Project

  • [noun - genetics & inheritance] The US Human Genome Project was a major scientific effort funded by the National Institutes of Health and the US Department of Energy. It began in 1990 with the scientific goals of identifying all of the genes in the human genome (approximately 25,000 total) and sequencing all 3 billion base pairs. Other major components of the project involved devising appropriate data storage and analysis tools for the information, and addressing the legal and ethical implications of the scientific work. The project, expected to last fifteen years, was completed in 2003, two years ahead of schedule.

  • hurricane

  • [noun - atmospheric science, weather & climate] Also called tropical cyclone; "hurricane" is the name used more commonly for tropical cyclones in the northern Atlantic Ocean basin and the eastern Pacific Ocean basin ("typhoon" is used commonly in the western Pacific). An intense, cyclonic storm that forms over warm, tropical ocean waters and then moves west and northeast. To reach hurricane status, sustained wind speeds must reach 73 mph, but they may reach up to 230 mph near the center of the storm.

  • Hutton, James

  • [person - landforms & geologic formations] Scottish geologist, chemist, and naturalist born in Edinburgh (1726-1797). Hutton is considered to be the father of modern geology. From his geologic observations, Hutton became convinced that the Earth was older than the Bible suggested. He also belonged to the uniformitarian school of thought, which held that changes to Earth's surface did not happen in sudden catastrophes, but rather occurred slowly, by processes that were continuously in effect. In 1795, he published his ideas in The Theory of the Earth, which was later popularized by John Playfair.

  • Huxley, Thomas Henry

  • [person - evolution & adaptation] English biologist born in Ealing, Middlesex (1825-1895). While serving in the Navy as an assistant surgeon, Huxley collected and studied marine invertebrates. He was so fierce a proponent of Darwin's theory of evolution by natural selection that he earned the nickname "Darwin's Bulldog." Huxley's most famous work is Evidence on Man's Place in Nature, published in 1863, which is the first attempt to apply the concept of evolution to the human race.

  • Huygens, Christian

  • [person - light & optics] Dutch mathematician born in The Hague (1629-1695). Huygens ground and polished his own telescope lenses, and in 1655, he detected the first moon of Saturn using one of them. He also proposed the theory that Saturn has rings. Huygens worked on a variety of other mathematical, scientific, and engineering problems, including the development of accurate pendulum clocks and gravitational theory. In 1678, he published his "Theory of Light" in which he argued that light is a wave, not a particle.

  • hybrid

  • [adjective - genetics & inheritance] Pertaining to the offspring of two plants or animals of different breeds, varieties, species, or genera. Hybrid often refers to plants or animals produced through selective breeding for specific genetic characteristics, such as plants that are bred to be drought resistant, or sheep that are bred to produce softer wool.

  • hydrocarbon

  • [noun - compounds, organic & biochemistry] An organic compound that contains only hydrogen and carbon.

  • hydrogen bond

  • [noun - atoms & subatomic particles, compounds] A strong dipole-dipole attraction between two or more molecules, at least one of which has a hydrogen atom bonded to an electron-withdrawing atom. More specifically, a weak bond formed between a hydrogen atom on one molecule which has developed a partial positive charge because of its bonding to an electronegative atom (commonly N, O, or F) and an electronegative atom on another molecule.

  • hydrogenation

  • [noun - biomolecules] A chemical process in which hydrogen is added to the double bonds of unsaturated fats, usually vegetable oils, to create a solid fat.

  • Hydronium ion

  • [acids, bases & pH] A positively charged water molecule that has taken on an additional proton, to be H-3O+.

  • hydrophilic

  • [adjective - biomolecules, physical & chemical properties] Literally meaning "water loving," a substance that readily associates with water. Often polar molecules or some ionic molecules that easily dissolve in or form solutions with water. Compare to hydrophobic.

  • hydrophobic

  • [adjective - biomolecules, compounds, physical & chemical properties] Literally meaning "water fearing," a substance that has little affinity for water. Generally, non-polar molecules that do not dissolve in or form solutions with water. Compare to hydrophilic.

  • hydrosphere

  • [noun - hydrology & fresh water, oceanography, weather & climate, biodiversity & ecological relationships, bioregions, biomes & ecosystems, human impacts on the environment, natural resources, nutrient cycles, weather & climate] All the water available on Earth and within Earth’s atmosphere, including (but not limited to) lakes, rivers, oceans, glaciers, aquifers, ice sheets, and clouds. See also: biosphere, lithosphere, atmosphere.

  • hydroxide ion

  • [noun - compounds] A negatively charged chemical compound that contains one hydrogen atom and one oxygen atom, written as OH-.

  • hydroxyl

  • [noun - compounds, organic & biochemistry, physical & chemical properties] An -OH group within a molecule.

  • Hypatia

  • [person] (355-415 CE, also called Hypatia of Alexandria) Greek philosopher, mathematician, and astronomer. Hypatia is the first woman scientist in history whose work and life details are known. She is remembered for commentaries on geometry and arithmetic, and for an astronomical table. She was an outspoken proponent of the idea that the human mind could make natural phenomena understandable.

  • hypotenuse

  • [noun - geometry] In a right triangle, the side that is opposite the right angle.

  • hypothesis

  • [noun - laws & theories, scientific tools & techniques, research methods] From the Greek word hypothesis meaning assumption or the basis of an argument, a hypothesis is a proposal intended to explain certain observations or phenomenon. In science, hypotheses represent the basis of scientific research, which is pursued to objectively determine whether or not a hypothesis is correct. Compare to theory.

Term of the day

cathode

[noun] A negatively charged terminal in an electrical cell.

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