area of science that aims at a comprehensive theory of the structure and evolution of the entire physical universe . Present models of the universe
Grouping of millions or billions of stars, held together by gravity. There are billions of galaxies in the universe . There are different types,
Luminous globe of gas, mainly hydrogen and helium, which produces its own heat and light by nuclear reactions. Although stars shine for a very long
Today, it has become widely accepted that our universe originated with the so-called big bang. This event marks the beginning of time and the further
change in the wavelength (or frequency) of energy in the form of waves, e.g., sound or light, as a result of motion of either the source or the
anything that has mass and occupies space. Matter is sometimes called koinomatter (Gr. koinos=common) to distinguish it from antimatter, or matter
in astronomy, celestial object of such extremely intense gravity that it attracts everything near it and in some instances prevents everything,
life history of a star , beginning with its condensation out of the interstellar gas (see interstellar matter ) and ending, sometimes
the sun and the surrounding planets, natural satellites , dwarf planets, asteroids, meteoroids, and comets that are bound by its gravity. The sun is
One of the 88 areas into which the sky is divided for the purposes of identifying and naming celestial objects. The first constellations were simple,
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gravitation
the attractive force existing between any two particles of matter . Since the gravitational force is experienced by all matter in the universe, from
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Variable stars
star that varies, either periodically or irregularly, in the intensity of the light it emits. Other physical changes are usually correlated with the
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Neutrinos
( nutrē'nō ) [Ital.,=little neutral (particle)], elementary particle with no electric charge and a very small mass emitted during the decay of certain
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Astronomy
branch of science that studies the motions and natures of celestial bodies, such as planets , stars , and galaxies ; more generally, the study of
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orbit
in astronomy, path in space described by a body revolving about a second body where the motion of the orbiting bodies is dominated by their mutual
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Nebulae
Cloud of gas and dust in space. Nebulae are the birthplaces of stars, but some nebulae are produced by gas thrown off from dying stars (see planetary
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observatory
scientific facility especially equipped to detect and record naturally occurring scientific phenomena. Although geological and meteorological
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Planets
[Gr.,=wanderer], a large nonluminous body of rock or gas that orbits the sun or another star, has a rounded shape due to gravity, and has cleared its
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Books
The word book has come to have many meanings, e.g., any collection of sheets of paper, wood, or other material sewn or bound together; a division of a
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quasar
( kwā'sär ), one of a class of blue celestial objects having the appearance of stars when viewed through a telescope and currently believed to be the
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radio telescope
Instrument for detecting radio waves from the universe in radio astronomy . Radio telescopes usually consist of a metal bowl that collects and focuses
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Biology
Science of life . Biology includes all the life sciences – for example, anatomy and physiology (the study of the structure of living things), cytology
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stellar populations
two broadly contrasting distributions of star types that are characteristic of different parts of a galaxy . Population I stars are young, recently
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Double stars
Pair of stars moving in orbit around their common centre of mass. Observations show that most stars are binary, or even multiple – for example, the
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telescope
traditionally, a system of lenses, mirrors, or both, used to gather light from a distant object and form an image of it. Traditional optical
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Zoology
branch of biology concerned with the study of animal life. From earliest times animals have been vitally important to man; cave art demonstrates the
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Milky Way
the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not
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hand
terminal part of the forelimb in primates. The human hand consists of the wrist, palm, four fingers, and thumb. In humans and other primates, the
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Population
the inhabitants of a given area, but perhaps most importantly, the human inhabitants of the earth (numbering about 7 billion in 2012), who by their
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Nuclear energy
Images of the electric grid, cooling towers, atomic bombs, and Hollywood productions serve as examples of what may come to mind when “nuclear energy”
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meteor
appearance of a small particle flying through space that interacts with the earth's upper atmosphere. While still outside the atmosphere, the particle
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Census
The term census usually refers to the complete process of preparation, collection, compilation, evaluation, analysis, and dissemination of data on
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Mythology
The word ‘mythology’ comes from the Greek words mythos , a story or legend, and logos , a discourse. It is used to describe bodies of traditional
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Comets
Small, icy body orbiting the Sun, usually on a highly elliptical path that takes it beyond the dwarf planet Pluto. A comet consists of a central
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Creation
In Judaism and Christianity, God's creation of the universe. It is described in Genesis 1 and 2, the first book of the Hebrew Bible (Old Testament).
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Relativity
physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two
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radiator
device used to heat an area surrounding it or to cool a fluid circulating within it. The familiar radiators of steam and hot water heating systems in
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Earth (Planet)
in geology and astronomy, 3rd planet of the solar system and the 5th largest, the only planet definitely known to support life. Gravitational forces
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Sun
Star at the centre of our Solar System. It is about 5 billion years old, with a predicted lifetime of 10 billion years; its diameter is 1.4 million
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rock
Constituent of the Earth's crust composed of minerals or materials of organic origin that have consolidated into hard masses. There are three basic
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pulsar
Celestial source that appears to flash at radio and other wavelengths at regular intervals, ranging from a few seconds to a few thousandths of a
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black body
in physics, an ideal black substance that absorbs all and reflects none of the radiant energy falling on it. Lampblack, or powdered carbon, which
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library
a collection of books or other written or printed materials, as well as the facility in which they are housed and the institution that is responsible
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Brown Dwarf
in astronomy, celestial body that is larger than a planet but does not have sufficient mass to convert hydrogen into helium via nuclear fusion as
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Energy
A system's capacity to do work. While energy is not visible, it is essential to all daily activities and takes on several different forms. The two
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exposition
or exhibition, term frequently applied to an organized public fair or display of industrial and artistic productions, designed usually to promote
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Nucleosynthesis
or nucleogenesis, in astronomy, production of all the chemical elements from the simplest element, hydrogen, by thermonuclear reactions within stars,
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Law
rules of conduct of any organized society, however simple or small, that are enforced by threat of punishment if they are violated. Modern law has a
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parallax
( pâr'əlăks ), any alteration in the relative apparent positions of objects produced by a shift in the position of the observer. In astronomy the term
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Moon
natural satellite of a planet (see satellite, natural ) or dwarf planet, in particular, the single natural satellite of the earth . The moon is the
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Nuclear fusion
Process in which two atomic nuclei are fused, with the release of a large amount of energy. Very high temperatures and pressures are required for the
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Botany
Study of living plants , including form, function, interaction with the environment, and classification. Botany is subdivided into a number of
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Nature
The totality of physical things considered distinct from the influences, activities and constructions of humanity. It is a complex concept with
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Nests
Place chosen or constructed by a bird or other animal for incubation of eggs, hibernation, and shelter. Nests vary enormously, from saucerlike hollows
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Aviation
operation of heavier-than-air aircraft and related activities. Aviation can be conveniently divided into military aviation, air transport, and general
