Astronomy, History of

• Astronomy, History of, history of the science that deals with all the celestial bodies in the universe. Astronomy includes the study of planets and their satellites, comets and meteors, stars and interstellar matter, star systems known as galaxies, and clusters of galaxies. The field of astronomy has developed from simple observations about the movement of the Sun and Moon into sophisticated theories about the nature of the universe.

Astronomical Constants

Constant

Value

Astronomical unit (au)	149,597,870 km
Speed of light in a vacuum (c)	299,792.458 km/sec
Solar parallax	8.794148 arc seconds
Mass of the sun	1.9891 × 1030 kg
Mass of the earth	5.9742 × 1024 kg
Mass of the moon	7.3483 × 1022 kg
Light-year (ly)	9.4605 × 1012 km = 0.30660 pc
Parsec (pc)	30.857 × 1012 km = 3.26161 ly
Obliquity of the eliptic (2000)	23 ° 26 ' 21.448 "
General precession (2000)	50.290966 arc seconds/year
Constant of nutation (2000)	9.2025 arc seconds
Constant of aberration (2000)	20.49552 arc seconds

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Callisto (astronomy)

• Callisto (astronomy), large satellite of the planet Jupiter. Callisto is the eighth known moon in distance from the planet. The moon orbits Jupiter at an average distance of 1,883,000 km (1,170,000 mi). Callisto completes an orbit and rotates in the same amount of time, once every 16.69 Earth days. Its nearly circular orbit parallels Jupiter’s equator.

• Callisto is spherical and is the third-largest moon in the solar system. The moon has a radius of 2,403 km (1,493 mi), making it nearly the same size as the planet Mercury. Since Callisto consists mostly of low-density water ice, however, the moon is only one-third as massive as rocky, metallic Mercury. Callisto’s interior is probably not differentiated into a rocky core surrounded by lighter icy material, like that of the other three large moons of Jupiter—Io, Europa, and Ganymede. Instead, scientists believe that the entire moon is a mixture of rock and ice, with the percentage of rock in the mixture increasing toward the moon’s center.

• Callisto is the most heavily cratered world known. This cratering suggests that the surface has not changed in billions of years and that there is little internal activity affecting it. If Callisto’s internal activity was strong enough, it would melt or disturb the ice near the moon’s surface, and many of the craters would be erased. Instead, Callisto seems to be the most geologically quiet of the four large moons of Jupiter. This is probably because Callisto is the outermost of the large moons. No large outer satellite of Jupiter subjects it to the gravitational tug-of-war with Jupiter that can produce internal heating.
  

• The only sign of change on the surface is the slumping of older crater walls that occurs as the ice that forms them flows downward over extremely long periods of time. Despite Callisto’s apparent stillness, however, in 1998 the Galileo spacecraft revealed signs that the moon may have a liquid or slushy ocean beneath its surface. Callisto may also have a tenuous atmosphere composed mostly of carbon dioxide.

• The largest crater on Callisto is Valhalla, a 300-km (190-mi) basin surrounded by a system of concentric rings 1,500 km (930 mi) wide. In addition, Callisto has 12 known crater chains. Astronomers believe that these chains were caused by comets or asteroids that broke up when they passed too near Jupiter and crashed into Callisto. The longest chain, Gipul Catena, is about 640 km (about 400 mi) long.

• Callisto was discovered independently by Italian astronomer Galileo and German astronomer Simon Marius. Callisto and the three other large moons of Jupiter—all of which were found in 1610—are collectively known as the Galilean moons. Marius named Callisto and the other Galilean moons for mythical lovers of the Greek god Zeus, whom the Romans renamed Jupiter. Callisto was a nymph who was changed into a bear by Zeus’s jealous wife Hera.
  

• In Greek mythology, Callisto is the basis of the constellation Ursa Major. Craters on Callisto are generally named for heroes and heroines of northern mythologies. The United States Voyager space probes and the United States Galileo orbiter have provided a wealth of information about Callisto. When the Voyager probes passed Jupiter in 1979 they provided some detailed photographs. Galileo made its first flyby of Callisto in 1996 and examined the moon several times before its mission ended in 2003.

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The 20 Brightest Stars as Seen from Earth

The 20 Brightest Stars as Seen from Earth

A star's brightness is referred to as its magnitude. "Apparent magnitude" is brightness as seen from Earth. The 20 stars with the highest aparent magnitudes are listed here. "Absolute magnitude" is intrinsic brightness as measured at a standard distance of 32.6 light-years or 10 parsecs from the star. The star with the highest absolute magnitude known in the universe, the Pistol Star, does not appear in this list because it is so far from Earth.

Scientific name

Common name

Distance (light-years)

Alpha Canis Majoris	Sirius	9
Alpha Carinae	Canopus	98
Alpha Centauri	Rigil Kent	4
Alpha Boötis	Arcturus	36
Alpha Lyrae	Vega	26
Alpha Aurigae	Capella	42
Beta Orionis	Rigel	910
Alpha Canis Minoris	Procyon	11
Alpha Eridani	Achernar	85
Alpha Orionis	Betelgeuse	510
Beta Centauri	Hadar	460
Alpha Aquilae	Altair	17
Alpha Tauri	Aldebaran	65
Alpha Crucis	Acrux	360
Alpha Scorpii	Antares	330
Alpha Virginis	Spica	260
Beta Geminorum	Pollux	36
Alpha Piscis Austrini	Fomalhaut	22
Alpha Cygni	Deneb	1,830
Beta Crucis	Mimosa	420
Alpha Leonis	Regulus	85

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Alpha Centauri

• Alpha Centauri, closest star system to Earth and third brightest star in the sky. Alpha Centauri is located in the constellation Centaurus and is sometimes called Rigil Kentaurus, which literally means “foot of the centaur.” Alpha Centauri is actually a triple star system that appears as a single point of light because its two largest and brightest members, Alpha Centauri A and Alpha Centauri B, are too close together for the naked eye to tell them apart and its third member, Alpha Centauri C, is too small and dim to be seen at all.

• The Alpha Centauri system is only visible from the Southern Hemisphere and the southernmost portion of the Northern Hemisphere. In Texas, Louisiana, and Florida, for example, it appears very low in the southern sky and is most easily visible in May.

• Alpha Centauri A and Alpha Centauri B lie about 4.35 light-years from Earth. A light-year is the distance light travels in a year, equal to about 9,460 billion km (5,880 billion mi). The two stars circle their common center of gravity, a point in space between them, about once every 80 years. The average distance between A and B is about 3.6 billion km (2.2 billion mi), which is a bit more than the average distance between the Sun and the planet Uranus.

• Alpha Centauri C orbits A and B at a tremendous distance—about 1,500 billion km (930 billion mi)—so far out that C takes millions of years to circle the two larger stars. Alpha Centauri C is also called Proxima Centauri; in the current portion of its orbit it is theclosest star to the solar system, at a distance of 4.2 light-years.

• Alpha Centauri A is a yellow star, slightly larger and brighter than the Sun, of spectral type G2 and apparent magnitude +0.01. Spectral type indicates a star’s surface temperature and the predominant color of the light it gives off. Apparent magnitude is a measure of how bright stars appear in the sky—a small, nearby star may appear just as bright as a much larger star that is farther away. The lower the apparent magnitude, the brighter the star appears. Alpha Centauri B is a yellow-orange star somewhat smaller and cooler than the Sun of spectral type K1 and apparent magnitude +1.34. Proxima Centauri is a red dwarf star of spectral type M5, much smaller and cooler than the Sun.

Spectral Types of Stars

Astronomers categorize stars according to the the characteristics of the light that the stars emit, which are related to the stars’ temperatures. O stars are the hottest stars, and M stars are the coolest. Our Sun is a G star.

Spectral Class

Effective Temperature Star Color

Principal Characteristics

O	25,000 K Blue star	This stage is characterized by lines of helium, oxygen, and nitrogen in the spectrum of the photosphere. O stars are extremely hot, very bright stars that emit large amounts of ultraviolet radiation.
B	11,000 K - 25,000 K White-blue star	In this group the lines of helium in the spectrum reach a maximum intensity and then fade. The intensity of the hydrogen lines regularly increases in all the subdivisions of stage B. Type B stars are typically represented by the star Epsilon Orionis.
A	7500 K - 11,000 K White star	This group comprises the so-called hydrogen stars. The spectra of these stars is dominated by absorption lines of hydrogen. Sirius, the Dog star, is a typical type A star.
F	6000 K - 7500 K Yellow-white star	This group is composed of stars characterized by an elevated intensity of the H and K lines of calcium and of lines characteristic of hydrogen. A notable star in this category is Delta Aquilae.
G	5000 K - 6000 K Yellow, solar star	This group is composed of stars with prominent H and K calcium lines and less prominent hydrogen lines. The spectra of numerous metals, in particular iron, are also present. The Sun belongs to this group, and therefore G stars are frequently called solar stars.
K	3500 K - 5000 K Orange-yellow star	This group comprises stars having strong calcium lines and lines indicating the presence of other metals in their spectra.The violet light of class K stars is less intense than the stars' red light. This group is typically represented by Arcturus.
M	3500 K Red star	This group is composed of stars whose spectra are dominated by bands resulting from the presence of metallic-oxide molecules, notably those of titanium oxide. The violet end of the spectra is less intense than that of K stars. The star Orionis is typical of this group.

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Aerospace Medicine

• Aerospace Medicine, branch of preventive medicine that is concerned with the physiological and psychological stresses on the human body in flight. The study of effects within the earth’s atmosphere is also called aviation medicine; beyond this atmosphere the study of effects is also called space medicine. Aerospace medicine was recognized as a subspecialty by the American Medical Association in 1953.

AVIATION MEDICINE

• Specialists in aviation medicine study the reactions of humans to the stresses of air travel. They are concerned with the proper screening of candidates for flight training, the maintenance of maximum efficiency among aircrews, and with clinically oriented research into the effects of flight on the body. They also cooperate actively with aeronautical engineers in the development of safe aircraft.

• Aviation medicine is rooted in the early 18th-century physiological studies of balloonists, some of whom were physicians. In 1784, a year after the first balloon flight by the French physicist Jean Pilâtre de Rozier, a Boston physician, John Jeffries, made the first study of upper-air composition from a balloon.

• The first comprehensive studies of health effects in air flight were made by the French physician Paul Bert, who published his research on the effects of altered air pressure and composition on humans in 1878 under the title La pression barometrique. In 1894 the Viennese physiologist Herman Von Schrötter designed an oxygen mask with which the meteorologist Artur Berson set an altitude record of 9150 m (30,000 ft).

• With the advent of the airplane, the first standards for military pilots were established in 1912. Significant work in this area was directed by the physician Theodore Lyster, an American pioneer in aviation medicine. Lyster set up the Aviation Medicine Research Board in 1917, which opened a research laboratory at Hazelhurst Field in Mineola, New York, in January 1918. The School of Flight Surgeons opened the following year, and in 1929 the Aero Medical Association was founded under the direction of Louis H. Bauer. In 1934 facilities were built at Wright Air Field in Dayton, Ohio, to study the effect of high-performance flight on humans.

• Technical advances included the first pressurized suit, designed and worn by the American aviator Wiley Post in 1934, and the first antigravity suit, designed by W. R. Franks in Britain in 1942. In an effort to help design better restraint systems for military jet aircraft, the U.S. flight surgeon John Stapp conducted a series of tests on a rocket-powered sled, culminating on December 10, 1954, when Colonel Stapp underwent deceleration from a velocity of 286 m (937 ft)/sec in 1.4 sec.

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Cockatiel

• Cockatiel, common name for a small, crested parrot native to Australia that is a popular pet. It is also known as a quarrion, weero, cockatoo parrot, or crested parrot. Cockatiels are gentle and affectionate birds that make good companions, especially when kept as solitary pets. Their soft call consists of a long, rolling kweel-kweel, but they can be taught to whistle basic melodies or speak simple words.

• Cockatiels in the wild live throughout Australia, but they are found mainly in the interior regions. They prefer open fields with groups of trees or bushes and a nearby water source. Australia bans the commercial export of this bird species. Cockatiels purchased as pets in other countries are the offspring of captive birds.

• From beak to tip of tail an adult cockatiel is a small bird, ranging in length from 29 to 34 cm (11 to 13 in) and weighing 75 to 125 g (3 to 4 oz). Male cockatiels (cocks) are larger than females (hens). In the wild, cockatiels display mostly slate-gray coloring. Cocks have a bright, lemon-yellow face and throat with prominent orange cheek patches and dark brown to black eyes.

• The pointed crest of cocks is predominantly yellow, with a grayish-yellow tint at the tip. Their white shoulder and wing patches contrast with a gray body; the beak and feet are also gray. The underside of the tail is black. Hens display similar but more subdued coloring, but the back and rump are a light gray with narrow white stripes. The underside of the tail is also striped with yellow and white markings.

• Genetic mutations and selective breeding have produced eight color varieties in captive cockatiels, described as pied, pearl, cinnamon, fallow, silver, lutino, whiteface, and albino. The pied cockatiel may be predominantly white or gray, with an irregular pattern of yellow, white, or gray feathers.
  

• The pearl cockatiel is primarily yellow with a checkered or scalloped pattern on the back and wings created by feathers with a yellow or white center and darker edges. Cinnamon and fallow cockatiels are both brown in color, with fallow a lighter brown than cinnamon. The silver cockatiel has metallic gray coloring and red eyes.
  

• The lutino cockatiel is mostly white or yellow, with dark red eyes, while the whiteface cockatiel is mostly gray and white with no yellow or orange. Albinos result from the combination of whiteface and lutino coloring. Combinations of these eight color variations are also common.

• In the wild, cockatiels band together in flocks of 12 to 100, but they may also occasionally travel in pairs. They are nomadic or migratory birds that follow the availability of food and water. Their diet consists of grains, fruits and berries, seedling grasses, and seeds.
  

• Cockatiels forage on the ground but are quick to fly up into trees to avoid birds of prey, their most common predators. Because large cockatiel flocks may devour fields of crops, some farmers consider cockatiels as pests.

• In northern Australia, the cockatiel mating season occurs from April to June; in southern Australia, cockatiels breed from August to December. During courtship, the cock displays his white shoulder patches to the hen, and he may drum his feet on the ground or a tree branch. If the hen flies away, the cock follows and repeats his display.
  

• Nests are built in hollow trees, usually eucalyptus trees, near fresh water. Both cock and hen take turns incubating the four to seven eggs, which hatch in about three weeks. Cockatiels are one of the few species of parrots in which both sexes share brooding responsibilities.

• Cockatiels do not display adult coloring until after their first molting (seasonal shedding of feathers) at six to nine months. They reach sexual maturity between 6 and 12 months. Cockatiels have an average life span of 12 to 15 years.

• Scientific classification: Cockatiels belong to the family Cacatuidae of the order Psittaciformes and are classified as Nymphicus hollandicus

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Angler

• Angler, common name for any of about 265 related saltwater fishes having appendages resembling fishing rods or lures with which they entice their prey. The common anglerfish is found along the coasts of Europe and North America from the British Isles and Nova Scotia to Barbados.

• Up to 1.5 m (about 5 ft) long, they live on the ocean floor, creeping along on modified pectoral fins in search of food. With a huge mouth and distensible stomach, an angler can swallow other fish as large as itself. In the United States certain anglers are also known as goosefishes and are often marketed under the name monkfish.
  

• Other groups of anglers include batfishes, frogfishes, and sea toads.

• One of the most unusual aspects of anglers is their reproductive behavior. In many species of deep-sea anglers, the male is less than one-tenth the size of the female and lacks her characteristic lure. The parasitic male attaches himself to the body of his mate by biting through the skin of the female host.
  

• The circulatory systems of the two fish then join, with nutrients from the blood of the female thereafter providing the male angler with his only source of nourishment. Anglers are the only fish that exhibit this type of extreme sexual dimorphism.

• Scientific classification: Anglers make up the order Lophiiformes. Those known as goosefishes make up the family Lophidae in the suborder Lophioidei, including the common anglerfish, or European goosefish, classified as Lophius piscatorius.
  

• Sexual dimorphism is characteristic of anglers belonging to the suborder Ceratioidei, often referred to as deep-sea anglers. Other groups of anglers include the batfish family, Ogcocephalidae, the frogfish family, Antennariidae, and the sea toad family, Chaunacidae.

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Ant

• Ant, common name for members of a family of about 11,000 species of insects that live in highly organized societies called colonies. Ant colonies have elaborate social structures in which the various activities necessary for the feeding, shelter, and reproduction of the colony are divided among specially adapted individuals. Ants belong to an order of insects called the Hymenoptera, a group that also includes bees, wasps, and sawflies.

• Some species of wasps and bees resemble ants in that they live in colonies and are therefore said to be social, but ants are the only hymenopterans in which every species is social. Ants are distinguished from other hymenopterans in that they have bent, or elbowed, antennae and an indented abdomen that forms a narrow waist.

• Ant colonies range in size from a few members to many millions of members. Members of an ant colony typically fall into categories known as castes, each with a different role. The majority of colony members are female worker ants that are unable to mate. Worker ants do not have wings and perform most of the work of the colony, including searching for food, nursing young, and defending the colony against ants from other colonies.
  

• Queens are larger than worker ants and are the only females of the colony capable of mating. Queens are born with wings, which they break off after mating. They mate with winged male ants, later using the sperm from the mating to produce fertilized eggs, which hatch to produce more worker ants and a new generation of queens. Aside from mating with the queens, males play no social role in colony life and die soon after mating.

• Ants live on landmasses all over the world, except for the permanently frozen Arctic and Antarctic, the coldest mountaintops, and a few islands. They flourish in soil, rotting wood, leaf litter, dead trees, and living trees in such varied habitats as mountains, deserts, swamps, and human homes. Ants are most abundant in the tropical regions.

• In the rain forests of the Amazon, for instance, ants are so numerous that their total weight is about four times the weight of all the area’s mammals, birds, reptiles, and amphibians combined.

• Ants play crucial roles in the ecosystems in which they live. Many species dig underground nests that have numerous openings and tunnels. Air and water pass into the soil through these passageways, making oxygen and moisture available to the roots of plants. Seed-eating ants remove seeds from plants and transfer them to underground storage chambers within their nests.

• This activity disperses the seeds, so that some of them can sprout in areas that are distant from the parent plants. Ants of many species feed on other insects, which may be either living or dead. In this way, ants reduce the size of some other insect populations and recycle organic matter.

• In turn, ants are a source of food for other animals, such as spiders, other insects, woodpeckers, and blue jays; toads, salamanders, and turtles; and anteaters, armadillos, and aardvarks. A few ant species are considered pests because they sting, invade human houses and yards, or damage wooden buildings.

Ant

Class	Insecta
Order	Hymenoptera
Family	Formicidae
Species	mississipiensis (American)
	sinensis (Chinese)
Conservation Concerns	45 species are at risk due to habitat destruction.
Range	Almost all parts of the world; most abundant in the tropics.
Habitat	Almost all parts of the world; most abundant in the tropics.
Feeding Habits	Most ants are omnivores; they eat plant juices, seeds, fruits, other insects, and honeydew, a sugary liquid secreted by aphids.
Offspring	Only queen ants lay eggs. Ants pass through egg, larva, pupa, and adult stages.
Life Span	Less than six months on average; some worker and queen ants live for several years.

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Ape

• Ape, any of 13 species of large, highly intelligent primates, including chimpanzees, gorillas, gibbons, and orangutans. Apes are sometimes confused with monkeys, but unlike their smaller primate counterparts, apes do not have tails and their arms are usually longer than their legs. Apes live in tropical woodlands and forests of Africa and Asia.

• Despite sharing similar habitats, different ape species show striking differences in behaviors and ways of life.

• At one time, apes were classified as a single group of primates, but today most zoologists divide them into two distinct families: the lesser apes, or gibbons, and the great apes. Gibbons are similar to monkeys, with lithe, slender bodies and extremely agile movements.

• Gibbons spend all of their lives in trees, using their hands like hooks to swing arm-over-arm between branches. Known as brachiation, this method of locomotion is so fast that gibbons can easily overtake a person running on the forest floor.

• The great apes include the gorilla, the orangutan, and two species of chimpanzee: the common chimp and the bonobo (sometimes called the pygmy chimpanzee). Great apes are bigger than gibbons and also much less acrobatic.

• However, they are still good climbers. While orangutans spend most of their life in trees, where they use their long arms and dexterous hands and feet to grasp branches and vines, chimpanzees frequently come to the ground to feed. Gorillas are primarily terrestrial, but even fully grown adult males have been observed clambering among tree branches more than 15 m (49 ft) high.

• Chimpanzees and gorillas—the apes that spend the most time on the ground—normally walk on all fours, clenching their hands so that their knuckles take their weight.From physical and fossil evidence, biologists know that apes and humans share a common ancestry.

• In recent years, biochemical analysis has shown just how close this link is—chimpanzees and humans differ significantly in only 2 percent of their genes. This evidence suggests that they diverged from a common ancestor around five to seven million years ago.

• Scientific classification: The gibbons make up the family Hylobatidae and the great apes make up the family Hominidae.

• The gorilla is classified as Gorilla gorilla, the common chimpanzee as Pan troglodytes, the bonobo as Pan paniscus, and the orangutan as Pongo pygmaeus.

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Bean

• Bean, common name widely applied to many plants of the legume family. The seeds and pods of these plants are used for food and forage. The seeds themselves are also called beans and are valuable as food because of their high protein content.

• The term bean is also applied to plants of other families, such as the Indian bean, which is a North American species, and the sacred bean, or Indian lotus (see Lotus). The seeds or fruits of certain other plants, such as the coffee tree and the castor-oil plant, are also called beans.

• The broad bean, also called horsebean or Windsor bean, has been cultivated since prehistoric times and is still the most common bean in many parts of Europe. Various species are cultivated in the United States under the name of vetch.
  

• Most of the beans of the United States and the frijoles of Mexico belong to the same genus. The cowpea, asparagus bean, and hyacinth bean are also cultivated, particularly for forage. The soybean is the common bean of the Orient and has been more widely cultivated in the United States in recent years than have native varieties of bean.
  

• Most soybeans are grown today for their oil, which is used in industrial manufacturing and as fodder for livestock.

• The wild bean of the United States is rarely cultivated. Hundreds of varieties of the common garden bean of the United States are cultivated. The young pods are called string, or snap, beans if green; they are called wax, or butter, beans if yellowish.
  

• The seeds of the older pods are known as shell beans. The small variety is often called navy bean and the large purplish variety, kidney bean.

• For cultivating, beans are divided into two groups: pole beans, or vines requiring a pole for support; and bush beans, erect shrubs of low, spreading growth. Many of the species, notably the common garden bean of the United States, have varieties in both groups, and the groups overlap one another.
  

• Although some of the bean plants are perennials, most of the important cultivated species are annuals and are sown in rich, loose, warm soil after all danger of frost is past.

• The principal disease affecting beans is a form of anthracnose caused by a fungus that attacks the stems, leaves, and pods of the bean. It is most visible on pods, in which it causes deep, dark pits. To prevent the disease, seeds are carefully selected, and care is taken not to spread the fungus from one plant to another during wet weather.
  

• A rust may defoliate bean plants. It first appears as small brown dots containing a brown powder, the spores of the fungus. Later the spots become larger and the spores black.

• Scientific classification: Most beans belong to the subfamily Papilionoideae of the family Fabaceae (formerly Leguminosae). The Indian bean is classified in the genus Catalpa. The broad bean is classified as Vicia faba.
  

• Vetch is classified in the genus Vicia. Most beans of the United States and the frijoles of Mexico are classified in the genus Phaseolus. Cowpeas and asparagus beans are classified in the genus Vigna. The hyacinth bean is classified as Lablab purpureus, the soybean as Glycine max, the wild bean of the United States as Phaseolus polystachios, and the common garden bean of the United States as Phaseolus vulgaris.
  

• The lima, or sugar, bean is generally classified as Phaseolus limensis, although it is regarded by some as a variety of the civet bean, classified as Phaseolus lunatus. The tepary is classified as Phaseolus acutifolius variety latifolius and the scarlet runner as Phaseolus coccineus.
  

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Amphibian (animal)

• Amphibian (animal), animal with moist, hairless skin through which water can pass in and out.

• Nearly all amphibians live the first part of their lives in water and the second part on land—a double life reflected in the name amphibian, which comes from the Greek words amphi, meaning “both,” and bios, meaning “life.”

• Amphibians were the first animals with backbones to adapt to life on land.

• They are the ancestors of reptiles, which in turn gave rise to mammals and birds.

• Scientists recognize more than 4,000 species of amphibians, all of which are members of one of three main groups: frogs and toads, salamanders, or caecilians.

• Frogs and toads are the most abundant of all amphibians, numbering more than 3,500 species. Frogs have smooth skin and long limbs.

• Toads, in contrast, have warty skin and short limbs.

• There are about 360 known species in the salamander group, which also includes newts and mud puppies.

• Members of this group have long, slender bodies ending in tails. Some salamanders live entirely on land, whereas others never leave the water, and still others spend some time in the water and some on land.

• Caecilians, with about 160 species, are the rarest of amphibians.

• They have no limbs and look much like earthworms.

• Most live underground and spend their time burrowing in the soil, but a few are aquatic.
  

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Alligator

• Alligator (Spanish el lagarto,”the lizard”), common name for two carnivorous reptiles in the crocodilian order.

• Alligators and their close relatives the caimans have broad, flat, and rounded snouts, as opposed to the longer, sharper snouts of other crocodilians; also unlike other crocodilians, their lower teeth cannot be seen when their mouths are closed.
• Alligators feed on fish, frogs, snakes, turtles, birds, mammals, and carrion. In North America they are also known to attack humans occasionally.

• Alligators can survive a wider range of temperatures than other crocodilians, and they are found in more temperate regions.

• Their breeding season is generally restricted to spring.

• Scientific classification: Alligators constitute the genus Alligator, family Crocodylidae.

• They are sometimes recognized as a separate family, Alligatoridae.

• The Chinese alligator is classified as Alligator sinensis and the American alligator as Alligator mississipiensis.

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Antelope

• Antelope, common name applied to a diverse group of hollow-horned mammals that belong to the same family as cattle, goats, and sheep.

• About 100 species of antelopes live in Africa and Asia, including some of the world's fastest and most elegant hoofed mammals, as well as some of the most endangered.
• In size, antelopes range from the tiny royal antelope, which stands about 25 cm (10 in) high at the shoulder, to the massively built common eland, which can weigh as much as 900 kg (nearly 2,000 lb)—more than an average car.
• Some better-known antelopes include impalas, gazelles, and gnus.Antelopes vary widely in their physical appearance and the way they live.
• Some antelopes, including many of the smallest species, stay close to vegetative cover and disappear into the undergrowth if disturbed, but most live in more open habitats where they rely on speed and alertness to escape attack.
• The species that flee also use their superb jumping skills to escape from predators: impalas, for example, can leap over fences 3 m (10 ft) high, and cover 10 m (33 ft) in a single bound.
• Some antelopes are solitary but most live in herds. In the late 1800s, herds of springbok in southern Africa sometimes included over 10 million animals that spread over a distance of 160 km (100 mi).
• Although herds no longer reach this astounding size today, antelopes still dominate life in African plains.
• They help grass thrive by nibbling away competing plants, and they provide food for predators and also for people.

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Sea Horse

• Sea Horse, any of a number of small fishes of the same family as the pipefish.

• The name is derived from the resemblance of the head to that of a horse.
• It has long, tubular jaws much like a snout.
• The body is compressed, with an elongated tail, and the integument (external covering) is a series of large, rectangular bony plates, with a series of spines and projections along the lines of juncture.
• These spines, together with the divided, streamerlike fins of some species, give them a strong resemblance to the seaweeds among which they live.
• About 30 species are found in various warm and temperate seas. All keep near the shore, often developing in brackish water.
• Like the pipefishes, the males take charge of the eggs, which are placed in an abdominal pouch and remain there until they hatch.
• The common sea horse of the Atlantic coast of North America is one of the largest species, reaching a length of more than 13 cm (more than 5 in).

Scientific classification:

• Sea horses make up the genus Hippocampus in the family Syngnathidae.
• The common sea horse is classified as Hippocampus hudsonius.

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Angelfish

• Angelfish, name used for several different fishes, including the true angelfishes and the butterfly fishes.

• Angelfishes differ from butterfly fishes in having a spine near the lower edge of the gill cover.
• These laterally compressed fishes are among the most beautiful of the tropical reef fishes.
• Most species are only a few centimeters long, but some grow to a length of 61 cm (24 in).
• In many species the juveniles and adults are colored differently; the young French angelfish of tropical Atlantic waters is black with bright yellow bands; the adult is predominantly black.
• The well-known queen angelfish is also differently colored as a juvenile.
• Most angelfishes feed on small invertebrates.
• Certain species are often called freshwater angelfish and are popular as aquarium fishes.
• In the United States a spadefish is sometimes incorrectly called an angelfish.

• Scientific classification: Angelfishes belong to the order Perciformes.
• True angelfishes make up the family Pomacanthidae. Butterfly fishes constitute the family Chaetodontidae.
• Freshwater angelfish belong to the family Cichlidae.
• French angelfishes are classified as Pomacanthus paru.
• Queen angelfishes are classified as Holacanthus ciliaris. Spadefishes are classified as Chaetodipterus faber.

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Astronomy

• Astronomy, study of the universe and the celestial bodies, gas, and dust within it.

• Astronomy includes observations and theories about the solar system, the stars, the galaxies, and the general structure of space.
• Astronomy also includes cosmology, the study of the universe and its past and future.
• People who study astronomy are called astronomers, and they use a wide variety of methods to perform their research.
• These methods usually involve ideas of physics, so most astronomers are also astrophysicists, and the terms astronomer and astrophysicist are basically identical.
• Some areas of astronomy also use techniques of chemistry, geology, and biology.
• Astronomy is the oldest science, dating back thousands of years to when primitive people noticed objects in the sky overhead and watched the way the objects moved.
• In ancient Egypt, the first appearance of certain stars each year marked the onset of the seasonal flood, an important event for agriculture.
• In 17th-century England, astronomy provided methods of keeping track of time that were especially useful for accurate navigation.
• Astronomy has a long tradition of practical results, such as our current understanding of the stars, day and night, the seasons, and the phases of the Moon.
• Much of today's research in astronomy does not address immediate practical problems.
• Instead, it involves basic research to satisfy our curiosity about the universe and the objects in it. One day such knowledge may well be of practical use to humans.

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Soil

• Soil, the loose material that covers the land surfaces of Earth and supports the growth of plants.
• In general, soil is an unconsolidated, or loose, combination of inorganic and organic materials.
• The inorganic components of soil are principally the products of rocks and minerals that have been gradually broken down by weather, chemical action, and other natural processes.
• The organic materials are composed of debris from plants and from the decomposition of the many tiny life forms that inhabit the soil.Soils vary widely from place to place.
• Many factors determine the chemical composition and physical structure of the soil at any given location.
• The different kinds of rocks, minerals, and other geologic materials from which the soil originally formed play a role.
• The kinds of plants or other vegetation that grow in the soil are also important.
• Topography—that is, whether the terrain is steep, flat, or some combination—is another factor.
• In some cases, human activity such as farming or building has caused disruption.
• Soils also differ in color, texture, chemical makeup, and the kinds of plants they can support.
• Soil actually constitutes a living system, combining with air, water, and sunlight to sustain plant life.
• The essential process of photosynthesis, in which plants convert sunlight into energy, depends on exchanges that take place within the soil.
• Plants, in turn, serve as a vital part of the food chain for living things, including humans.
• Without soil there would be no vegetation—no crops for food, no forests, flowers, or grasslands. To a great extent, life on Earth depends on soil.

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Alexander Graham Bell

• Alexander Graham Bell (1847-1922), American inventor and teacher of the deaf, most famous for his work on the telephone.

• Bell was born on March 3, 1847, in Edinburgh, Scotland, and educated at the universities of Edinburgh and London.
• He immigrated to Canada in 1870 and to the United States in 1871. In the United States he began teaching deaf-mutes, publicizing the system called visible speech.
• The system, which was developed by his father, the Scottish educator Alexander Melville Bell, shows how the lips, tongue, and throat are used in the articulation of sound.
• In 1872 Bell founded a school to train teachers of the deaf in Boston, Massachusetts.
• The school subsequently became part of Boston University, where Bell was appointed professor of vocal physiology.
• He became a naturalized U.S. citizen in 1882.Since the age of 18, Bell had been working on the idea of transmitting speech.
• In 1874, while working on a multiple telegraph, he developed the basic ideas of the telephone.
• His experiments with his assistant Thomas Watson finally proved successful on March 10, 1876, when he transmitted: “Watson, come here; I want you.” Subsequent demonstrations, particularly one at the 1876 Centennial Exposition in Philadelphia, Pennsylvania, introduced the telephone to the world and led to the organization of the Bell Telephone Company in 1877.
• In 1880 France bestowed on Bell the Volta Prize, worth 50,000 francs, for his invention.
• With this money he founded the Volta Laboratory in Washington, D.C., where, in that same year, he and his associates invented the photophone, which transmits speech by light rays.
• Other inventions include the audiometer, used to measure acuity in hearing; the induction balance, used to locate metal objects in human bodies; and the first wax recording cylinder, introduced in 1886.
• The cylinder, together with the flat wax disc, formed the basis of the modern phonograph.
• Bell's continuing studies on the causes and heredity of deafness led to experiments in eugenics, including sheep breeding, and to his book Duration of Life and Conditions Associated with Longevity (1918).
• He died on August 2, 1922, at Baddeck, where a museum containing many of his original inventions is maintained by the Canadian government.

National Inventors Hall of Fame

The National Inventors Hall of Fame is a U.S. organization founded in 1973 to honor successful inventors. Members are chosen by the selection committee of the National Inventors Hall of Fame Foundation, which is composed of representatives from national scientific and technical organizations.

Date of selection

Inventor

Invention

1973	Thomas Alva Edison	electric lamp
1974	John Bardeen, Walter Brattain, William Shockley	transistor
	Alexander Graham Bell	telegraphy and telephone
	Eli Whitney	cotton gin
1975	William Coolidge	vacuum tube
	Guglielmo Marconi	transmitting electric signals
	Samuel Morse	telegraph signals
	Nikola Tesla	electromagnetic motor
	Orville Wright, Wilbur Wright	flying machine
1976	Rudolf Diesel	internal combustion engine
	Enrico Fermi	neutronic reactor
	Charles Goodyear	improvement in India-rubber fabrics, vulcanization of rubber
	Charles Hall	manufacture of aluminum
	Cyrus McCormick	mechanical reaper
	Charles Townes	maser
1977	Lee De Forest	audio amplifier
	George Eastman	coating plates for use in photography
	Edwin Land	instant processing photography
	Charles Steinmetz	system of electrical distribution
	Vladimir Zworykin	cathode-ray tube
1978	Luis Alvarez	radio distance and direction indicator
	Leo Baekeland	synthetic resin
	Carl Djerassi	oral contraceptive
	Louis Pasteur	brewing beer and ale
1979	Jay Forrester	random access memory (RAM)
	Robert Goddard	rocket science
	Charles Plank, Edward Rosinski	improved gasoline manufacture
1980	Edwin Armstrong	frequency modulation (FM) radio broadcasting
	James Hillier	electron lens correction device
	Charles Kettering	engine starting devices and ignition system
	Lewis Sarett	synthetic cortisone
1981	Harold Black	negative feedback amplifier
	Chester Carlson	xerography
	Charles Draper	gyroscopic apparatus
	Nikolaus Otto	gas motor engine
1982	Henry Ford	transmission mechanism
	Jack Kilby	integrated circuit
	Ernest Lawrence	cyclotron
	Ottmar Mergenthaler	linotype machine
	Max Tishler	riboflavin, sulfaquinoxline
1983	Ernest Alexanderson	high-frequency alternator
	Andrew Alford	localizer antenna systems
	Herbert Dow	process of extracting bromine
	Robert Noyce	semiconductor device and lead structure
	George Stibitz	complex computer
1984	William Burton	manufacture of gasoline
	Wallace Carothers	nylon
	Philo Farnsworth	television system
	Theodore Maiman	laser
1985	Marvin Camras	magnetic recording
	Willis Carrier	air conditioning
	René Higonnet, Louis Moyroud	phototypesetter
	Willem Kolff	artificial heart
	Roy Plunkett	Teflon
1986	Luther Burbank	strain of peach
	Harold Edgerton	stroboscope
	Wilson Greatbatch	heart pacemaker
	Donalee Tabern, Ernest Volwiler	Pentothal, Nembutal
1987	Arnold Beckman	apparatus for testing acidity
	William Burroughs	calculating machine
	Andrew Moyer	method for production of penicillin
	Igor Sikorsky	helicopter controls
1988	Frank Colton	oral contraceptive
	Elisha Otis	safety elevator
	Louis Parker	television receiver
	An Wang	magnetic pulse controlling device
1989	Raymond Damadian	magnetic resonance imaging
	John Deere	steel plow
	Irving Langmuir	incandescent electric lamp
	George Westinghouse	steam-power brake device
1990	George Washington Carver	cosmetics, paint, and stain
	Graham Durant, John Emmett, C. Robin Ganellin	antiulcer compounds and compositions
	Charles Ginsburg	videotape recorder
	Herman Hollerith	punched card tabulating system
	Eugene Houdry	liquid fuels
	Percy Julian	cortisone synthesis
	Robert Ledley	diagnostic X-ray system
	Kenneth Olsen	magnetic core memory
1991	Willard Bennett	radio frequency mass spectrometer
	Gertrude Elion	antileukemia drug
	Gordon Gould	optically pumped laser amplifier
	Leonard Greene	airplane stall warning device
	William 'Butch' Hanford, Donald Holmes	polyurethane
	Elmer Sperry	gyroscopic compass
	Robert Williams	synthesis of vitamin B1
1992	Lloyd Conover	tetracycline
	Frederick Cottrell	electrostatic precipitator
	William Hewlett	audio oscillator
	Benjamin Rubin	bifurcated vaccination needle
1993	Baruch Blumberg, Irving Millman	test and vaccine for hepatitis B
	John Ericsson	propeller
	William Lear	automobile radio
	Robert Maurer, Donald Keck, Peter Schultz	fiber optics
	John Parsons	numerical control of machine tools
1994	Emile Berliner	gramophone/microphone
	Robert Hall	magnetron
	Elizabeth Hazen, Rachel Brown	nystatin
	Robert Rines	high-resolution imaging-scanning radar and sonar
	Heinrich Rohrer, Gerd Binnig	scanning tunneling microscope
1995	Joseph H. Burckhalter, Robert J. Seiwald	dyes for diagnosing infectious disease
	Stephanie L. Kwolek	Kevlar polymers and fibers
	Waldo L. Semon	polyvinyl chloride plastisols
	John Sheehan	semisynthetic penicillin
	William Stanley	electric transformer
	Forrest M. Bird	fluid control device, respirator, pediatric ventilator
1996	H. M. Edmund Germer	discharge device, high-pressure vapor lamp
	Ted Hoff, Stanley Mazor, Federico Faggin	microprocessor concept and architecture
	Julius Arthur Nieuwland	vinyl derivatives of acetylene and methods of preparation
	Arthur Leonard Schawlow	masers and maser communications system
	Leo Szilard	neutronic reactor
1997	Edward Goodrich Acheson	carborundum
	Robert W. Bower	field-effect device with insulated gate (MOSFET)
	George H. Babcock, Stephen Wilcox, Jr.	water-tube steam boiler
	Seymour Cray	supercomputer
	Mark Dean, Dennis Moeller	improvements in computer architecture allowing computer components to communicate with each other in a high-speed and efficient manner
	Robert H. Dennard	dynamic random access memory (DRAM)
1998	Henry Timken	tapered roller bearing
	Alfred Nobel	dynamite
	Joseph Begun	magnetic recording
	Douglas Engelbart	computer mouse and development of modern computer environment
	James Fergason	liquid-crystal display
	Kary Mullis	polymerase chain reaction (PCR)
1999	Percy LeBaron Spencer	microwave oven
	Donald L. Campbell, Homer Z. Martin, Eger V. Murphree, Charles W. Tyson	fluid catalytic cracking
	George de Mestral	Velcro
	Gerhard Sessler, James Edward West	foil electret microphone
	Bryan B. Molloy, Klaus K. Schmiegel	Prozac
2000	Walt Disney	multiplane camera
	Reginald Fessenden	radiotelephony
	Alfred Free, Helen Free	glucose detection for diabetes
	J. Franklin Hyde	method of making a transparent article of silica
	William Kroll	method for manufacturing titanium and related alloys
	Stephen Wozniak	microcomputer for use with video display
2001	Robert Banks, Paul Hogan	polymers
	Herbert Boyer, Stanley Cohen	genetic engineering
	Oliver Evans	high-pressure steam engine
	Thomas Fogarty	embolectomy catheter
	Elijah McCoy	automatic engine lubricator
	Patsy Sherman, Sam Smith	Scotchgard
	Christopher Sholes	typewriter
2002	Raymond Kurzweil	Kurzweil reading machine
	Nils Bohlin	3-point safety belt
	Rangaswamy Srinivasan, James Wynne, Samuel Blum	excimer laser surgery
	Drs. M. Stephen Heilman, Alois Langer, Morton Mower, Michel Mirowski	implantable defibrillator
	Dr. Rodney Bagley, Dr. Irwin Lachman, Ronald Lewis	ceramic substrate for catalytic converters
	Felix Hoffmann	aspirin
	Dr. John Presper Eckert, Jr., John Mauchly	electronic numerical integrator and computer (ENIAC) data translating device
	Henry Bessemer	Bessemer steel process
2003	George Carruthers	far electrograph ultraviolet camera
	Frank Cepollina	satellite servicing techniques
	Glenn Curtiss	hydroaeroplane
	Maxime Faget	space capsule design
	Leroy Grumman	retractable landing gear; folding wing
	Charles H. Kaman	rotor control mechanism for rotary aircraft
	Paul Kollsman	altimeter
	Edwin A. Link	link trainer/simulator
	Thomas Midgley, Jr.	ethyl gasoline
	John Northrop	flying wing plane; all-metal high-wing monocoque airplane (Vega)
	John Pierce	communications satellite
	Harold Rosen	spin stabilized synchronous communications satellite
	Theodore von Kármán	turbo jet
	Hans J. P. von Ohain	jet engine
	Richard Whitcomb	supercritical wing
	Sir Frank Whittle	jet engine
	Sam Williams	small fan-jet engine
2004	Frederick Banting, Charles Best, James Collip	Insulin for diabetics
	Vannevar Bush	Differential Analyzer
	Harry Coover	superglue
	Wallace Coulter	blood counter
	Ray Dolby	noise reduction systems
	Edith Flanigen	molecular filters for petroleum processing
	Robert Gallo, Luc Montagnier	HIV isolation and diagnosis
	Ivan Getting, Bradford Parkinson	Global Positioning System (GPS)
	John Gibbon	heart-lung machine
	Lloyd Hall	food preservation techniques
	Elias Howe	sewing machine
	Charles Kelman	cataract eye surgery
	Bernard Oliver, Claude Shannon	Pulse Code Modulation
	Norbert Rillieux	modern sugar refining
	John Roebling	modern suspension bridge
Source: National Inventors Hall of Fame.

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