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Pluto, in astronomy

(Encyclopedia)Pluto, in astronomy, a dwarf planet and the first Kuiper belt, or transneptunian, object (see comet) to be discovered (1930) by astronomers. Pluto has an elliptical orbit usually lying beyond that of ...

bursa, in anatomy

(Encyclopedia)bursa bûrˈsə [key], closed fibrous sac lined with a smooth membrane, producing a viscous lubricant known as synovial fluid. Bursas are found in regions where muscles or tendons rub against other mu...

field, in physics

(Encyclopedia)field, in physics, region throughout which a force may be exerted; examples are the gravitational, electric, and magnetic fields that surround, respectively, masses, electric charges, and magnets. The...

triangle , in music

(Encyclopedia)triangle, in music, percussion instrument consisting of a steel rod bent into a triangle, open at one angle, and struck with a steel rod. Only since the end of the 18th cent. has it been an orchestral...

Mass, in Christianity

(Encyclopedia)Mass, religious service of the Roman Catholic Church, which has as its central act the performance of the sacrament of the Eucharist. It is based on the ancient Latin liturgy of the city of Rome, now ...

Ganymede, in astronomy

(Encyclopedia)Ganymede gănˈēmēdˌ [key], in astronomy, one of the moons, or natural satellites, of Jupiter; the largest natural satellite in the solar system, it is larger than the planet Mercury. ...

category, in philosophy

(Encyclopedia)category, philosophical term that literally means predication or assertion. It was first used by Aristotle, whose 10 categories formed a list of all the ways in which assertions can be made of a subje...

tenure, in education

(Encyclopedia)tenure, in education, a guarantee of the permanence of a college or university teacher's position, awarded upon successful completion of a probationary period, usually seven years. Tenure is designed ...

proof, in mathematics

(Encyclopedia)proof, in mathematics, finite sequence of propositions each of which is either an axiom or follows from preceding propositions by one of the rules of logical inference (see symbolic logic). Mathematic...

archangel, in religion

(Encyclopedia)archangel ärkˈānjəl [key], chief angel. They are four to seven in number. Sometimes specific functions are ascribed to them. The four best known in Christian tradition are Michael, Gabriel, Raphae...