Astronomy
Astronomy, which etymologically means laws of the
stars, is the science whose subject is the observation and
explanation of events outside the
earth. Astrophysics is the part of astronomy (and
physics) that deals with the application of
physics to the phenomena observed by astronomy. Nearly all astronomers
now have a strong background in physics, and the results of observations are
usually put in an astrophysical context, so astronomy and astrophysics are
used with a very close meaning.
Astronomy is one of the few sciences where
amateurs still play an active role, especially in the discovering and
monitoring of transient phenomena.
Astronomy is not to be confused with
astrology, a
pseudoscience which attempts to predict a person's destiny by tracking the
paths of astronomical objects. Although the two fields share a common origin,
they are quite different; astronomy embraces the
scientific method, while astrology does not.
Given its huge scope, astronomy is divided into different branches. The
divisions are not unique, however, and the intersections, as well as astronomers
who work in several areas, are the rule more than the exception.
A first distinction is between theoretical and observational
astronomy and astrophysics. Observers use a variety of means to obtain data
about different phenomena, data that is then used by theorists to create and
constrain theories and models, to explain observations and to predict new ones.
Fields of study are also categorized in another two main ways: by subject,
usually according to the region of space (e.g. Galactic astronomy) or problems
addressed (such as star formation or cosmology); and according to the means of
obtaining the data (e.g. optical astronomy or radioastronomy)
Many of the important subfields of astronomy have their own Wikipedia
articles, such as the following:
See
list of astronomical topics for a more exhaustive list of astronomy-related
pages.
In astronomy, the main way of obtaining information is through the detection and
analysis of
electromagnetic radiation,
photons, but we also receive information from outside the earth carried by
cosmic rays,
neutrinos, and, in the near future,
gravitational waves (see
LIGO and
LISA[?]).
A traditional division of astronomy is given by the region of the
electromagnetic spectrum observed:
-
Optical astronomy refers to the techniques used to detect and analyze
light in and slightly around the
wavelengths than can be detected with the
eyes (about 400 - 800 nm). The most common tool is the
telescope, with
electronic imagers and
spectrographs.
-
Infrared astronomy deals with using infrared radiation (wavelengths
longer than the red light). Again, the most common tool is the
telescope, but with instruments sensitive to longer wavelengths; the
telescope itself can be optimized for infrared. Space telescopes are also
used to eliminate noise ( electromagnetic interference) from the atmosphere.
-
Radio astronomy uses completely different instruments to detect
radiation of wavelengths of mm to cm. The receivers are similar to those
used in
radio broadcast transmission (which uses those wavelengths of
radiation). See also
Radio telescopes.
-
High-energy astronomy
Optical and radio astronomy can be done using ground-based
observatories, because the
atmosphere is transparent at those wavelengths. Infrared light is heavily
absorbed by
water vapor, so infrared observatories have to be located in high, dry
places or in space.
The atmosphere is opaque at the wavelengths used by
X-ray astronomy,
gamma-ray astronomy,
UV astronomy and, except for a few wavelength "windows",
Far infrared astronomy , and so observations can be carried out only from
balloons or
space observatories.
In the early part of its history, astronomy involved only the observation and
predictions of the motions of the objects in the sky that could be seen with the
naked eye. The
ancient Greeks made many important contributions to astronomy, among them
the definition of the
magnitude system. They also defined the
Zodiac, a band of twelve bright
constellations.
The study of astronomy almost stopped during the middle ages, except for the
work of some
Arabic astronomers. The
renaissance came to astronomy with the work of
Copernicus, who proposed a
heliocentric model of the
Solar System. His work was defended, expanded upon, and corrected by the
likes of
Galileo Galilei and
Johannes Kepler. The latter of these was the first to provide a system which
described correctly the details of the motion of the planets with the Sun at the
center. However, Kepler did not understand the reasons behind the laws he wrote
down. It was left to
Newton's invention of
celestial dynamics and his
law of gravitation, the final explanation of the motions of the
planets. Astrophysics was a later development, which only became possible
once it was understood that the elements that made up the "celestial objects"
were the same that made up the
Earth, and that the same
laws of physics applied.
Stars were found to be far away objects, and with the advent of
spectroscopy it was proved that they were similar to our own sun, but with a
wide range of
temperatures,
masses and sizes. The existence of our
galaxy, the
Milky Way, as a separate group of stars was only proven in the 20th century,
along with the existence of "external" galaxies, and soon after, the expansion
of the
universe seen in the recession of most galaxies from us.
Cosmology, a discipline that has a large intersection with astronomy, made
huge advances during the 20th century, with the model of the hot
big bang heavily supported by the evidence provided by astronomy and
physics, such as the
cosmic microwave background radiation,
Hubble's Law and
cosmological abundances of elements.
For a more detailed history of astronomy, see the
history of astronomy.
See also :
Astronomers and Astrophysicists,
Amateur Astronomy,
History of astronomy,
Theoretical astrophysics
See also:
