Stars
A star is a large ball of hot gas, thousands to millions of kilometers
in diameter, emitting large amounts of radiant energy from nuclear
reactions in its interior. differ fundamentally from planets in that
they are self-luminous, whereas planets shine by reflected sunlight. Except
for the SUN, which is the nearest star, stars appear only as points of
light, even in the largest telescopes, because of their distance.
The brightest stars have long been given names. Most of the familiar
names originated with the ancient Greeks or with later Arab astronomers; an
entirely different system was used by the Chinese, starting hundreds of
years earlier, about 1000 BC. Polaris, the North Star, ...
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lettered names, such as RR
Lyrae in the constellation Lyra. Fainter stars are known by their numbers
in a catalog; HD 12938 is the 12,938th star in the Henry Draper Catalogue.
CHARACTERISTICS OF STARS
Each star in the universe has its own position, motion, size, mass,
chemical composition, and temperature. Some stars are grouped into clusters,
and stars and star clusters are collected in the larger groupings called
galaxies. Our GALAXY, the Milky Way, contains more than 100 billion stars.
Because tens of millions of other galaxies are known to exist, the total
number of stars in the universe exceeds a billion billion.
Positions, Motions, and Distances
Stars are seen in the same relative positions, night after night, year
after year. They provided early astronomers with a reference system for
measuring the motions of planets ("wandering stars"), the Moon, and the Sun.
The westward rotation of the celestial sphere simply reflects the daily
eastward rotation of the Earth, ...
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(3.3 light-years). Most of the measured
distances are greater than 20 parsecs (65 light-years), which shows why the
average star in the sky is so much fainter than the nearby Sun.
Brightness and Luminosity
Star brightness was first estimated by eye, and the brightest stars in
the sky were described as "stars of the first magnitude." Later, the
magnitude scale was defined more accurately: 6th magnitude stars are just
1/100 as bright as 1st magnitude stars; 11th magnitude stars are 1/100 as
bright as 6th magnitude, and so on. The magnitude scale is logarithmic;
that is, each magnitude corresponds to a factor of 1/2.54, because (1/2.54)
to the power of 5 =1/100 (see MAGNITUDE).
...
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Stars. (2007, April 8). Retrieved November 23, 2024, from http://www.essayworld.com/essays/Stars/63057
"Stars." Essayworld.com. Essayworld.com, 8 Apr. 2007. Web. 23 Nov. 2024. <http://www.essayworld.com/essays/Stars/63057>
"Stars." Essayworld.com. April 8, 2007. Accessed November 23, 2024. http://www.essayworld.com/essays/Stars/63057.
"Stars." Essayworld.com. April 8, 2007. Accessed November 23, 2024. http://www.essayworld.com/essays/Stars/63057.
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