Astronomy
Science dealing with the origin, evolution, composition,
distance, and motion of all bodies and scattered matter in the universe.
The most ancient of the sciences, it has existed since the
dawn of recorded civilization. Much of the earliest knowledge of celestial
bodies is often credited to the Babylonians. The ancient Greeks introduced
influential cosmological ideas, including theories about the Earth in relation
to the rest of the universe. Ptolemy's model of an Earth-centred universe (2nd century
AD) influenced astronomical thought for over 1,300 years. In the 16th century,
Nicolaus Copernicus assigned the central position to the Sun (see Copernican
system), ushering in the age of modern astronomy. The 17th century saw several
momentous developments: Johannes Kepler's discovery of the principles of
planetary motion, Galileo's application of the telescope to astronomical
observation, and Isaac Newton's formulation of the laws of motion and
gravitation. In the 19th century, spectroscopy and photography made it possible
to study the physical properties of planets, stars, and nebulae, leading to the
development of astrophysics. In 1927 Edwin Hubble discovered that the universe,
hitherto thought static, was expanding (see expanding universe). In 1937 the
first radio telescope was built. The first artificial satellite, Sputnik, was
launched in 1957, inaugurating the age of space exploration; spacecraft that
could escape Earth's gravitational pull and return data about the solar system
were launched beginning in 1959 (see Luna; Pioneer). See also big bang;
cosmology; gamma-ray astronomy; infrared astronomy; radio and radar astronomy;
ultraviolet astronomy; X-ray astronomy.
Source: Britannica encyclopedia
