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The apparent change in direction of a celestial source of light caused by an observer's component of motion perpendicular to the impinging rays. In astronomy, aberration manifests, for example, as a star appearing aberrantly from what its true…

Technologies to optimize the performance of optical systems wherein controllable optical elements maintain a sharply focused image in the presence of wavefront aberrations. The practical development of adaptive optics started in the late 1960s. Main…

A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from…

An ongoing current event in which a large number of living species are threatened with extinction or are going extinct because of environmentally destructive human activities. The Earth is presently in the midst of a mass extinction event. In the…

One of the many hundreds of thousands of small planets (technically called minor planets) revolving around the Sun, mainly between the orbits of Mars and Jupiter. Asteroids are rocky bodies varying greatly in size from less than 10 meters across (33…

A neurodevelopmental condition that impairs the way that a person relates to and communicates with other people. Persons with autism have difficulties with social communication and interaction. They also can have unusual behaviors, such as…

Light emitted by a high-speed charged particle when the particle passes through a transparent, nonconducting, solid material at a speed greater than the speed of light in the material. The emission of Cerenkov radiation—also spelled Cherenkov—is…

The internal structures and processes that are involved in the acquisition and use of knowledge, including sensation, perception, attention, learning, memory, language, thinking, and reasoning. The mental processes and behaviors that constitute…

A psychotherapy with roots in both cognitive science and behavioral science. Cognitive-behavioral therapy (CBT) is the most widely used evidence-based psychotherapeutic practice for a variety of mental health disorders, including anxiety, depression…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

A syndrome characterized by a generalized decline in cognition that is severe enough to cause functional impairment in daily activities. Dementia is a term used to describe a collection of symptoms of severe cognitive decline. Individuals suffering…

The interaction of the behavior and ecology of hosts with the biology of pathogens as relating to the impact of diseases on populations. Although human diseases have been studied from an ecological perspective for centuries, diseases in plant and…

The spinning of the Earth upon its planetary axis and movement of the Earth around the Sun. While appearing constant, the Earth's rate of rotation, where one complete rotation is measured as a day, and the rate of the Earth orbital motion around the…

A term commonly associated with both behaviors and states of mind (known as feelings) that are not under the control of reason and disturb the flow of consciously directed behavior. Emotions influence human thinking and behavior (Fig. 1), and they…

One of the two places in the sky where the ecliptic crosses the celestial equator, or one of the two times of the year when the Sun crosses these points. The ecliptic is the great circle across the sky that marks the mean path of the Sun; the…

Planets beyond our solar system. For millennia, humankind has known about most of the major planets in our solar system because these worlds are visible to the naked eye. Exoplanets, however, were not indisputably known until 1995, when astronomers…

A plant that has altered genetic material (DNA) through recombinant DNA (rDNA) manipulation. Genetic engineering of plants allows for very specific genetic changes to be made to a plant's deoxyribonucleic acid (DNA), as opposed to the random…

A commercially grown plant that has altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…

A biological organism whose genetic material has been manipulated artificially through genetic or genomic editing techniques. In contrast to the long history of artificial selection (domestication), in which humans selectively breed organisms to…

A species translocated from one region or continent to another outside its normal range, particularly when the translocation is the result of human activity (intentional or otherwise). Many thousands of species, including animals, plants, fungi,…

A large space telescope optimized for observations in infrared wavelengths through science operations in cryogenic conditions. Designed for addressing a range of astrophysical and cosmological questions, the James Webb Space Telescope, or JWST, in…

A space telescope mission dedicated to detecting exoplanets. The tenth mission launched under the National Aeronautics and Space Administration's (NASA's) Discovery Program, Kepler was the agency’s first mission dedicated to the search for planets…

The planet fourth outward from the Sun and the planet most like Earth in terms of geology, climate, and suitability for life. Mars is nicknamed the "Red Planet" for its reddish hue (Fig. 1). Besides Earth, Mars is the most-studied world in the solar…

The mental ability to store and access information that has been acquired through experience. Memory (Fig. 1) is a critical component of practically all aspects of human thinking, including perception, learning, language, and problem solving.…

A slow change in the direction of the axis of rotation of the Earth as well as a very small change in the orientation of the Earth's orbit around the Sun. As a consequence of the precession of equinoxes, both the celestial equator (the projection of…

The second largest planet in the solar system and the sixth in order of distance from the Sun. The outermost planet known prior to 1781 CE, Saturn is surrounded by a system of rings far more extensive than any other in the solar system (Fig. 1), as…

An instrument used to collect, measure, or analyze electromagnetic or other radiation from distant objects. A telescope overcomes the limitations of the human vision by increasing the ability to see faint objects and discern fine details. In…

A plant, Musa textilis, of the banana family that is valuable for its hard fiber (also known as Manila hemp). Abaca (Musa textilis) is a flowering plant native to the Philippines and Borneo. Taxonomically, it is assigned to the order Zingiberales.…

An increase in the expansion rate of the universe, attributed to dark energy. In 1998, astronomers presented evidence that the universe's expansion is not slowing down, as would be expected due to the gravity from the abundances of matter strewn…

Habituation to a specific practice, such as drinking alcoholic beverages or using drugs (for example, heroin, cocaine, or amphetamines), and disorders characterized by the chronic use of a drug, alcohol, or similar substance. Addiction and addictive…

Any disorder of recognition. Agnosia is a rare neurological condition in which an individual fails to recognize and identify persons or objects (see illustration). Typically, agnosia is the result of damage to specific areas of the brain.…

Mechanized systems of food and fiber production used in agriculture. The mechanized systems comprising agricultural machinery are utilized in numerous aspects of agriculture, including the initial tillage of the soil (Fig. 1), planting, cultural…

The repeated and/or excessive use of alcohol (ethanol) that continues despite negative physical, psychiatric, or social consequences. Alcoholism is characterized by consuming alcohol more often, in larger amounts, or over longer periods than…

A small, tropical, evergreen tree (Pimenta dioica) and its dried, unripe fruit (berry). Allspice (Pimenta dioica; alternatively, P. officinalis) [see illustration] is a member of the myrtle family (Myrtaceae). Allspice, which is also known as…

Any of the plant growth forms characteristic of the upper reaches of mountain slopes. Alpine vegetation refers to the plants that grow in mountainous areas above the limit of subalpine trees and other subalpine vegetation. In such environments,…

An intergrading region on a mountain slope characterized by specific plant life forms or species composition, and determined by complex environmental gradients. Along an altitudinal transect of a mountain, there are sequential changes in the…

A significant, yet relatively selective loss of memory. Amnesia is a type of memory loss, often resulting from brain disease or injury (see illustration). The inability to remember can be temporary or permanent. In general, amnesia can be…

The use of live nonhuman animals for scientific research and experimentation. Animal testing has been a cornerstone of biomedical research, having contributed greatly to the understanding of human biology, to the unraveling of the complex underlying…

A disorder of language acquired as a result of brain disease. Aphasia is impairment in the use of spoken or written language caused by brain disorders (see illustration) that cannot be explained by paralysis or incoordination of the articulatory…

The application of ecological principles to the solution of human problems and the maintenance of a high quality of life. Applied ecology is a branch of ecology that applies concepts of ecology to address contemporary problems involving natural…

An impairment in the performance of voluntary actions despite intact motor power and coordination, sensation and perception, and comprehension. Apraxia is a neurological condition in which there is difficulty with skilled tasks or learned movements…

Any vegetable that is prevalent in Asian cuisines, but less well known in Western diets. Asian vegetables (Fig. 1), also referred to as Asian greens or oriental vegetables, are very important in Asian countries, but are not as popular in North…

The study of the universe and the objects in it through scientific investigation. The goal of astronomical research is to understand celestial objects and the nature and evolution of the cosmos (Fig. 1). Because much of contemporary astronomy uses…

The study of the stars, galaxies, and other objects outside of the Solar System, with attention to physical causes. Astrophysics developed in the late 19th century, taking over from the mere mapping of positions of objects that had been the…

A device that uses an internal resonance frequency of atoms (or molecules) to measure the passage of time. Atomic clocks (Fig. 1) are relied on internationally as the most accurate time and frequency standards with myriad uses in commerce, industry,…

A common psychiatric disorder (especially in children) characterized by attentional difficulties, impulsivity, and hyperactivity. Attention deficit hyperactivity disorder (ADHD) is a mental disorder marked by an individual's inability to pay…

Any of several leguminous plants, or their seeds, long utilized as food by humans or livestock. There are more than 40,000 varieties of beans, with only a small number of these being mass-produced for human or animal consumption. In particular,…

The drug as well as the plant known as deadly nightshade (Atropa belladonna). The belladonna plant (Atropa belladonna; see illustration) belongs to the nightshade family, Solanaceae, in the order Solanales. The plant is a coarse and poisonous…

The theory that the universe began in a hot, dense state and has since expanded and cooled. The big bang is the generally accepted cosmological theory for the origin, properties, and evolution of the universe (Fig. 1). Cosmology Universe 1 Timeline…

The number of different plant and animal species living in a defined ecosystem or study area; a contraction of biological diversity. Biodiversity includes genetic diversity (variability in the genetic makeup among individuals in a single species),…