red giant, star that is relatively cool but very luminous because of its great size. All normal stars are expected to pass eventually through a red-giant phase as a consequence of stellar evolution. As a star uses up its hydrogen by converting it to helium, its central core contracts while the outer layers expand and cool; this process produces the low temperature and large size (from 10 to 1,500 times that of the sun) that characterize the red giant. Although most giant stars are red, some prominent giant stars are other colors near the red end of the spectrum, e.g., Arcturus (orange), Aldebaran (orange), and Capella (yellow). The largest and brightest stars (excluding supernovas) are classed as supergiants. Blue supergiants, e.g., Rigel, are young stars on the main sequence of the Hertzsprung-Russell diagram, whereas red supergiants, e.g., Betelgeuse and Antares, are old, highly evolved stars.

giant star: see red giant.

giant sequoia: see sequoia.

giant schnauzer: see schnauzer.

giant orders: see orders of architecture.

giant clam, common name for the largest bivalve mollusk in the world, Tridacna gigas, also known as the bear's paw clam. The giant clam may weigh over 500 lb (225 kg) and attain a length of over 4 ft (120 cm). The heavy shell is coarsely fluted and toothed. Giant clams are found in the South Pacific and Indian oceans, especially in the Great Barrier Reef. They lie with the hinge downward in the coral reefs, usually in shallow water. The adductor muscles, which cause the shell to close, are a source of food for people of the South Pacific. The shell closes very slowly; stories of human beings trapped within giant clams have never been substantiated. Small giant clam shells have been used as birdbaths and baptismal fonts. An interesting symbiosis occurs between a unicellular green alga (Zooanthella) and the clam. The algae live in the tissues of the clam's siphon and mantle; they are able to obtain the sunlight needed for photosynthesis because the clam lies with its valves opening upward and part of the thick, purple mantle extruding over the shell. In addition, there are crystalloid vesicles on the mantle surface that let in sunlight, thus allowing the algae to live deep within the tissues. The clam uses the algae as a supplementary or perhaps even a major source of food. Tridacna gigas is classified in the phylum Mollusca, class Pelecypoda or bivalvia, order Eulamellibranchia, family Tridacnidae.

giant, in mythology, manlike being of great size and strength. The giant has been the symbol for the expression of certain recurring beliefs in the mythologies of all races. He is universally represented as being a brutish power of nature, lacking the stature of gods and the civilization and cunning of men. Among the myths of such different cultures as the Greeks, the Scandinavians, and the Native Americans of the Great Plains, giants were believed to be the first race of people that inhabited the earth. Two of the most familiar legends concerning giants are those of Jack the Giant Killer and David and Goliath.

Giant Sequoia National Monument: see National Parks and Monuments (table).

Star with a relatively large radius for its mass and temperature; this yields a large radiating area, so such stars are bright. Subclasses include supergiant stars, red giants (with low temperatures, but very bright), and subgiants (with slightly reduced radii and brightness). Some giants are hundreds of thousands of times brighter than the Sun. Giants and supergiants may have masses 10–30 times that of the Sun and volumes millions of times greater and are thus low-density stars.

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or giant sequoia or Sierra redwood

Coniferous evergreen (Sequoiadendron giganteum; see conifer) found in scattered groves on the western slopes of the Sierra Nevada range of California, U.S. The largest of all trees in bulk, the big tree is distinguished from the coastal redwood (Sequoia sempervirens) by having uniformly scalelike, or awl-shaped, leaves that lie close against the branches, scaleless winter buds, and cones requiring two seasons to mature. The pyramidal tree shape, reddish brown furrowed bark, and drooping branches are common to both genera. The largest specimen (in total bulk) is the General Sherman tree in Sequoia National Park—101.5 ft (31 m) in circumference at its base, 272.4 ft (83 m) tall, and weighing an estimated 6,167 tons (5,593 metric tons). Because big-tree lumber is more brittle than redwood lumber and thus less desirable, the big tree has been easier to preserve; though some groves have been cut, most of the 70 remaining groves are now protected by state or national forests or parks.

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or cat bear or bear cat

Long-tailed nocturnal raccoonlike carnivore (Ailurus fulgens, family Procyonidae) that inhabits high mountain forests in the Himalayas and adjacent eastern Asia. It is 20–26 in. (50–65 cm) long, excluding the 12–20-in. (30–50-cm) bushy, faintly ringed tail. It weighs 6–10 lbs (3–4.5 kg) and has soft, thick, reddish brown fur. The face is white, with a red-brown stripe from the eyes to the mouth. It eats plants, especially bamboo, and fruits and insects. Though an agile climber, it mostly feeds while on the ground.

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or giant order

Architectural order in which the columns extend beyond one interior story, often through several stories. Though giant columns were used in antiquity, they were first applied to building facades in Renaissance Italy. Any of the orders might be treated in this manner. The colossal order was revived in 18th-century Europe.

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