While the word "satellite" simply means some object or person that is attendant to another more important object or person, in astronomy it has taken on a much more specific meaning. Here the term refers to any object that is orbiting another larger more massive object under the influence of their mutual gravitational force. Thus any planetary moon is most properly called a satellite…
A savanna is a plant community characterized by a continuous grassy layer, often with scattered trees or shrubs, that is subject to regular, severe drought and occasional bush fires. A savanna is also the flat, open landscape in which such plant communities thrive. The word savanna comes from the Taino word zabana, which was used to describe a grassy, treeless plain. (Taino was the language of a n…
Savants are people with extremely outstanding abilities, often in music, mathematics, memory, or art. Their talents stand in marked contrast to their intelligence in other areas, which is well below normal. For example, a savant who, given any date in the past hundred years, could say what day of the week it fell on, might not be able to perform simple tasks like tying his shoes or catching a bus.…
Sawfish are marine shark-like cartilaginous fish in the family Pristidae in order Rajiformes. Sawfish are characterized by their long snout nose which has sharp teeth on each side. Like other rays, sawfish lurk to attack schools of prey fish with its long snout, and devour the injured fish. The long snout also serves as a defensive weapon, inflicting serious injury on any enemy attacking it. Sawfi…
The saxifrages, currants, and gooseberries are about 40 genera and about 850 species of plants that make up the family Saxifragaceae. These plants occur in all parts of the world, but are most diverse and prominent in arctic, boreal, and montane habitats of North America and Eurasia. The largest genera in the family are the saxifrages (Saxifraga spp.), of which there are about 300 species, most of…
A scalar is a number or measure, usually representing a physical quantity, that is not dependent upon direction. For example, distance is a scalar quantity since it may be expressed completely as a pure number without reference to spacial coordinates. Other examples of scalar quantities include mass, temperature, and time. The term scalar originally referred to any quantity which is measurable on …
Scale insects, mealybugs, or coccids are a diverse group of species of insects in the superfamily Coccoidea, order Homoptera. The females of scale insects are wingless, and are also often legless and virtually immobile. For protection, female scale insects are covered by a scale-like, waxy material. Like other homopterans, scale insects are herbivores with piercing mouth parts that are used to suc…
A scanner is a computer accessory (peripheral) used to digitize pictures. A scanner converts a visual image to a digital signal. The signal is interpretable by computer software, which allows the image to be recorded, manipulated, and even sent electronically to another computer. Even in the early 1990s, computers were used more for "in house" functions, such as preparing documents.…
Scarlet fever (sometimes called scarletina), is a bacterial disease, so named because of its characteristic bright red rash. Before the twentieth century, and the age of antibiotics, scarlet fever (at one time called "the fever") was a dreaded disease and a leading cause of death in children. The disease is caused by a group A beta-hemolytic streptococcus bacteria (genus Streptococcu…
A scavenger is an animal that seeks out and feeds upon dead and/or decaying organic matter. Some scavengers specialize on feeding upon dead animals, or carrion, while others feed more generally on dead plants and animals. Scavengers are part of the detrital food web of ecosystems. Scavengers provide a very important ecological service, because they help to rapidly reduce dead animals and plants to…
Schizophrenia is a psychotic disorder (or a group of disorders) marked by severely impaired thinking, emotions, and behaviors. The term schizophrenia comes from two Greek words that mean "split mind." It was coined around 1908, by a Swiss doctor named Eugen Bleuler, to describe the splitting apart of mental functions that he regarded as the central characteristic of schizophrenia. (N…
Like a rapacious and relentlessly predatory science fictional entity assimilating all it encounters (the Star Trek Borg come to mind), science fiction in the early twenty-first century is an unstoppable expansive force that is certainly not limited to one particular genre. Science fiction literature, once ghettoized and marginalized, is pervasive and ever more rapidly garnering respect. PMLA, Amer…
The history of science as an academic discipline grew in the post-1945 era along with the development of higher education and the expansion of science and technology. In the United States, Vannevar Bush's seminal 1945 article, "Science, the Endless Frontier: A Report to the President," called for a government-supported national research foundation. Bush's influence led …
The most familiar characteristics of modern science—rigorously demonstrated relationships based on a combination of experimentation and exact measurement—did not exist anywhere in the world before the seventeenth century. Any definition of science that holds for earlier times or for places other than Europe must be more inclusive. More useful criteria are the attempt to find rational…
Scientific thought aims to make correct predictions about events in nature. Although the predictive nature of scientific thought may not at first always be apparent, a little reflection usually reveals the predictive nature of any scientific activity. Just as the engineer who designs a bridge ensures that it will withstand the forces of nature, so the scientist considers the ability of any new sci…
The scorpion fly, despite its name, is neither a scorpion nor a fly. The name is a suggestion of the general appearance of the insect. They have four membranous wings that are the same size and shape. The head is rather elongated and points down in a beak-like fashion with the chewing mouthparts located at the tip of the beak. The genital segment of the male scorpion fly has an enlarged, rounded a…
Scorpionfish are ray-finned bony marine fish belonging to the family Scorpaenidae. Most of the 300 species of scorpionfish live in the seas around North America. A major anatomical characteristic of scorpionfish is a bony structure extending from the eye to the operculum or gill cover. The common name of scorpionfish refers to the spiny condition of the members of this family which includes extrem…
Screamers are three species of large birds in the family Anhimidae. This family is in the order Anseriformes, which also includes the ducks, geese, and swans, although screamers bear little superficial resemblance to these waterfowl. Screamers are non-migratory birds that inhabit a wide range of aquatic habitats in the tropics of South America, especially marshy places. Screamers are large birds, …
Screwpines are shrubs, trees, or vines belonging to the family Pandanaceae in order Pandanales, and the class Arecidae, which also includes the palms. Screwpines are native to the tropics of South and Southeast Asia, northern Australia, and west Africa. Despite their common name, screwpine are not related to the true pines, which are gymnosperms of the phylum Coniferophyta. Screwpines are common e…
The sculpins are about 300 species of small, rather grotesquely shaped fish that make up the family Cottidae. Most species of sculpins occur in cold or cool-temperate marine waters of the Northern Hemisphere, but a few species occur in fresh waters of northern Asia, Europe, and North America. Sculpins are short, stout-bodied fishes, with a large and broad head, large eyes, a large mouth, and broad…
Sea anemones are invertebrate animals belonging to the phylum Coelenterata, a term that means hollow gut. Sea anemones are found in all major oceans from the polar regions to the equator. All are exclusively marine-dwelling with a strong tendency for shallow, warm waters. More than 1,000 species have been described so far. These vary considerably in size, with a body diameter that ranges from just…
Sea cucumbers are echinoderms, belonging to the class Holothuroidea of the order Echinodermata. About 1,000 species have been described, which vary in size from only 1.2 in (3 cm) to more than 3.3 ft (1 m) in length. Sea cucumbers occur in all of the oceans, being found in waters up to 655 ft (200 m) in depth, and perhaps deeper. In appearance, these animals range from an almost spherical to long …
Sea horses are bony fish (or teleosts) in the family Syngnathidae, which includes about 230 species in 55 genera, most of which are pipefishes. The "true" sea horses comprise some 25 species in the genera Hippocampus and Phyllopteryx, which make up the subfamily Hippocampinae. Species of sea horses occur in warm-temperate and tropical waters of all of the world's oceans. The u…
To most people sea level is the point at which the surface of the land and sea meet. Officially known as the sea level datum plane, it is a reference point used in measuring land elevation and water depths. It refers to the vertical distance from the surface of the ocean to some fixed point on land, or a reference point defined by people. Sea level became a standardized measure in 1929. Mean sea l…
Resembling a plant more than an animal, sea lilies are some of the most attractive but least-known animals of the deep oceans. Sea lilies are members of the class Crinoidea (phylum Echinodermata), a class that also includes the feather stars. Sea lilies are also related to more familiar echinoderms such as sea urchins, starfish, and sea cucumbers. Unlike these small, squat forms, however, the main…
Sea lions are large marine mammals in the family Otariidae, sub-order Pinnipedia, order Carnivora, found now along the Pacific and South Atlantic coasts and on many islands of the southern hemisphere. Sea lions may have appeared first on the Pacific shores during the Lower Miocene. They are less fully adapted to aquatic life than are the true seals (family Phocidae of the same sub-order Pinnipedia…
Sea spiders (phylum Arthropoda, class Pycnogonida) are a group of arthropods that take their common name from their superficial resemblance to the true spiders. Although rarely seen, these are widespread animals occurring in every ocean, with a preference for cooler waters. Sea spiders occupy a wide range of habitats: some species have been recorded from a depth of 19,685 ft (6,000 m), but the maj…
Classified within the same phylum (Chordata), sea squirts and salps belong to separate classes, the Ascidiacea and Thaliacea, respectively. Both groups are also known as tunicates, a group of primitive chordates which have a primitive feature known as the notochordthe earliest and simplest equivalent to the vertebrae of more developed animals. In appearance adult sea squirts and salps are barrel-s…
Sea urchins (phylum Echinodermata) are small marine species that have a worldwide distribution. All are free-living and solitary in nature; some 800 species have been identified to date. The body is characterized by its rounded or oval shape and, in most species, by the presence of large numbers of sharp spines of varying lengths. The underside is usually flattened in contrast to the convex upper …
Seals are large carnivorous marine mammals in the order Pinnipedia that feed on fish, squid, and shell-fish; some even feed on penguins. They are aquatic animals that spend time on shores and ice floes. Seals have streamlined bodies and webbed digits, with the forelimbs acting as flippers, while the hind limbs are backwardly directed in swimming and act as a propulsive tail. A small tail is also p…
Seamounts are submarine mountains, often volcanic cones, that project 150-3,000 ft (50-1,000 m) or more above the ocean floor. They are formed primarily by rapid undersea buildups of basalt, a dark, fine-grained rock that is the main component of the ocean's crust. Seamounts form by submarine volcanism. After repeated eruptions, the volcano builds upwards into shallower water. If a seamount…
Seasonal winds are movements of air repetitively and predictably driven by changes in large-scale weather patterns. Seasonal winds occur in many locations throughout the world. The name assigned to a particular seasonal wind—and the underlying physical forces that drive the winds—depend upon the unique geographic location. One of the most commonly recognized seasonal winds are the mo…
Seasons on Earth are found only in the temperate zones. These zones extend from 23.5° north (and south) latitude to 66.5° north (and south) latitude. In these regions of Earth nature exhibits four seasons; spring, summer, autumn (or fall) and winter. Each season is characterized by differences in temperature, amounts of precipitation, and the length of daylight. Spring comes from an …
Secondary pollutants are not emitted directly to the air, water, or soil. Secondary pollutants are synthesized in the environment by chemical reactions involving primary, or emitted chemicals. The best known of the secondary pollutants are certain gases that are synthesized by photochemical reactions in the lower atmosphere. The primary emitted chemicals in these reactions are hydrocarbons and gas…
The secretary bird (Sagittarius serpentarius) is the only member of the family Sagittariidae. This family is part of the Accipitriformes, which includes other hawk-like raptors such as hawks, eagles, vultures, kites, falcons, and the osprey. The secretary bird is native to sub-Saharan Africa, and occurs in open grasslands and savannas. The species is wide-ranging, and some populations are nomadic,…
The terms secularization and secularism have had a variety of meanings since they were coined; "secularization" in the mid-seventeenth century and "secularism" in the mid-nineteenth, both incorporating the word secular. "Secular," from the Latin "saeculum," a generation or age, originally referred to secular clergy who were not in a monastic …
Sediments are loose Earth materials such as sand that accumulate on the land surface, in river and lake beds, and on the ocean floor. Sediments form by weathering of rock. They then erode from the site of weathering and are transported by wind, water, ice, and mass wasting, all operating under the influence of gravity. Eventually sediment settles out and accumulates after transport; this process i…
Sedimentary rocks form at or near the Earth's surface from the weathered remains of pre-existing rocks or organic debris. The term sedimentary rock applies both to consolidated, or lithified sediments (bound together, or cemented) and unconsolidated sediments (loose, like sand). Although there is some overlap, most sedimentary rocks belong to one of the following groups-clastic, chemical, o…
The seed ferns are an extinct group of plants known technically as the Pteridospermales. As indicated by their name, the seed ferns had leaves which were fernlike in appearance, and they reproduced by making seeds. Some seed ferns resembled tree ferns (family Cyatheaceae), a still-living group of tropical plants which are treelike in appearance but which reproduce by making spores. The seed ferns,…
Seeds are the products of the sexual reproduction of plants, and for this reason the genetic information of seeds is influenced by both of the parents. Sexual reproduction is important for two reasons. The first involves the prevention of the loss of potentially important genetic information, a process that occurs when non-sexual means of propagation are prevalent. The other benefit of sexual repr…
Segmented worms (phylum Annelida) are so named because of their elongated, more or less cylindrical bodies divided by grooves into a series of ringlike segments. Typically, the external grooves correspond to internal partitions called septa, which divide the internal body space into a series of compartments. Perhaps the most familiar examples of segmented worms are the common earthworms or night c…
Seismographs today consist of three essential parts. One is a seismometer, a device (like the seismoscope) that detects earth movements. A second component is a device for keeping time so that each earth movement can be correlated with a specific hour, minute, and second. The third component is some device for recording the earth movement and the time at which it occurred. The written record produ…
Selection refers to an evolutionary pressure that is the result of a combination of environmental and genetic pressures that affect the ability of an organism to live and, equally importantly, to raise their own reproductively successful offspring. As implied, natural selection involves the natural (but often complex) pressures present in an organism's environment. Artificial selection is t…