AcronymJ Definition
PASJ Publications of the Astronomical Society of Japan
PASJ Performance Acoustical Society of Japan
PASJ Pediatric Ambulance Saint-Jean
PASJ People Against The State Of Jersey
PASJ pour la solidarité et la justice ("Alliance for democracy in Mali/African
Party for solidarity and justice
PASJ Page Author Stupid (web design) of Japan
PASJ Panic Attack Syndrome of Japan
PASJ Parental Alienation Syndrome of Japan
PASJ Paris Airshow of Japan
PASJ Paros, Greece - Paros Community (Airport Code) of Japan
PASJ Parti Islam Se-Malaysia (Islamic Party of Malaysia) of Japan
PASJ Partia Agrare e Shqip?ris? (Agrarian Party of Albania) of Japan
PASJ Partido Alianza Social (Spanish: Social Alliance Party, Mexico) of Japan
PASJ Partitioned Annotations of Software (web-based sharing environment) of
Japan
PASJ Pascal Source Code (File Name Extension) of Japan
PASJ Passive Alcohol Sensor of Japan
PASJ Passive Ambiguity Surface of Japan
PASJ Passive and Active Gas-Liquid Separator Devices of Japan
PASJ Patient Administration System (hospitals) of Japan
PASJ Pediatric Academic Societies of Japan
PASJ People Are Stupid of Japan
PASJ Percussive Arts Society of Japan
PASJ Performance Accountability System of Japan
PASJ Performance Algorithm Shifting (Cadillac automotive transmission
technology) of Japan
PASJ Performance Assessment System of Japan
PASJ Periodic Acid-Schiff (medical technology: stain used to detect
carbohydrates in tissue) of Japan
PASJ Peripheral Anterior Synechiae of Japan
PASJ Personal Access Services (Bellcore) of Japan
PASJ Personal Accounting System of Japan
PASJ Personal Alert System of Japan
PASJ Personal Amplification System of Japan
PASJ Personal Assistant Services (disabled and mature community) of Japan
PASJ Personal de Administración y Servicios (Spanish) of Japan
PASJ Personnel Access System of Japan
PASJ Personnel Accounting Symbol of Japan
PASJ Personnel Accounting System (USMC) of Japan
PASJ Personnel Automation Section of Japan
PASJ Pharmacy Analytical Services of Japan
PASJ Phased Announcement System (4ESS) of Japan
PASJ Philanthropic Advisory Service (now part of Wise Giving Alliance) of Japan
PASJ Philippine Academy of Sakya of Japan
PASJ photoacoustic spectrometer/spectroscopy of Japan
PASJ Physician Assisted Suicide of Japan
PASJ Physicians for Automotive Safety of Japan
PASJ Physics Academic Software of Japan
PASJ Pilot Alert System of Japan
PASJ Pilotage Application System of Japan
PASJ Planning and Scheduling
PASJ Planning Assistance to States
PASJ Pod Aft Section
PASJ Point and Shoot (camera)
PASJ Policyholder and Agency Systems (insurance)
PASJ Polish Academy of Sciences
PASJ Pollution Abatement System
PASJ Polyarylsulfone
PASJ Population Analysis Spreadsheets
PASJ Portable Antiquities Scheme (UK)
PASJ Position Announcement System (Sprint)
PASJ Positron Annihilation Spectroscopy
PASJ Post-Abortion Syndrome
PASJ Power Amplifier Symposium (IEEE)
PASJ Power Assisted Steering
PASJ Power Azimuth Spectrum
PASJ Pre-Award Survey
PASJ Precision Acquisition System
PASJ Preliminary Alcohol Screening
PASJ Premises Appear Secure
PASJ Presence and Availability Server
PASJ Presidential Airlift Squadron
PASJ Presidential Appointee in a Position Requiring Senate Confirmation (federal
government ethics)
PASJ Presidential Arts Scholarship
PASJ Pricing Advisor System (insurance)
PASJ Primary Alerting System
PASJ Privacy Act Statement
PASJ Privilege Attribute Server
PASJ Process Automation Systems
PASJ Product Assessment Service
PASJ Product Attribute System (NRF)
PASJ Product of Ambulatory Surgery
PASJ Production Application Support
PASJ Professional Animal Scientist
PASJ Professor of Aerospace Studies
PASJ Profile Alignment System
PASJ Project Acquisition Strategy
PASJ Protected Aircraft Shelter
PASJ Protected Areas Strategy (forestry industry)
PASJ Proud Arabian Stallion (Breyer mold)
PASJ Provoked A Smile
PASJ Pseudo Aircraft Simulation
PASJ Public Access System
PASJ Public Address System
PASJ Publicly Approved Submitter
PASJ Publicly Available Specification
PASJ Push Application Server
The Alliance for Democracy in Mali-Pan-African Party for Liberty, Solidarity and
Justice (Alliance pour la Démocratie en Mali-Parti Pan-Africain pour la Liberté,
la Solidarité et la Justice, ADEMA-PASJ) is a political party in Mali.
On October 25, 1990 opponents of the dictatorship of Moussa Traoré joined
together as ADEMA. This umbrella movement included activists of the following
organizations:
* Sudanese Union/African Democratic Rally (Soudanaise-Rassemblement Démocratique
Africain, US-RDA), party of the former president Modibo Ke?ta
* the Malian Party for Revolution and Democracy (le Parti malien pour la
révolution et la démocratie, PMDR)
* the Malian Party of Labour (le Parti malien du travail, PMT), a
Marxist-Leninist organization
* the Malian Popular and Democratic Front (le Front démocratique et populaire
malien, FDPM), composed primarily of Malian emigrants and political exiles
ADEMA also attracted many supporters with no previous political affiliation.
On May 25, 1991, after the regime of Moussa Traoré was overthrown by General
Amadou Toumani Touré, ADEMA transformed itself into an official political party
and took the name Alliance for Democracy in Mali-African Party for Solidarity
and Justice (ADEMA-Parti Africain pour la Solidarité et la Justice, ADEMA-PASJ).
In 1992, ADEMA-PASJ dominated the February and March legislative elections,
claiming 76 of 116 seats in the Malian National Assembly. Its presidential
candidate, Alpha Oumar Konaré, was elected President of the Republic. ADEMA-PASJ
continued to dominate the government for the following decade, and Konaré was
re-elected in 1997 following an opposition boycott of the polls.
At the end of Konaré's second term, ADEMA-PASJ divided over the succession of
the presidency, with Ibrahim Boubacar Ke?ta leaving the party in October 2000 to
form the Rally for Mali (Rassemblement pour le Mali, RPM). Former prime minister
Mandé Sidibé also left in order to enter the presidential race.
In 2002, Souma?la Cissé was the official presidential candidate of ADEMA-PASJ.
He won 22.7 % of the vote in the first round of the presidential election, held
on 28 April, and was defeated by Amadou Toumani Touré in the second round, held
on 12 May, receiving 35.7 % of the vote. In the parliamentary election held on
14 July 2002, the party won 45 out of 160 seats. 6 additional seats were won by
partners in the Alliance for Republic and Democracy.
ADEMA-PASJ backed Touré for re-election in the April 2007 presidential election.
This was opposed by party vice-president Soumeylou Boubèye Maiga, who was
consequently expelled from the party. In the July 2007 parliamentary election,
ADEMA-PASJ won 51 out of 147 seats, more than any other party.
ADEMA-PASJ's motto is "Work-Solidarity-Justice"; its symbol is the bee. The
current party president is Dioncounda Traoré.
ADEMA-PASJ is a full member of the Socialist International.
Astronomy is the scientific study of celestial objects (such as stars, planets,
comets, and galaxies) and phenomena that originate outside the Earth's
atmosphere (such as the cosmic background radiation). It is concerned with the
evolution, physics, chemistry, meteorology, and motion of celestial objects, as
well as the formation and development of the universe.
Astronomy is one of the oldest sciences. Astronomers of early civilizations
performed methodical observations of the night sky, and astronomical artifacts
have been found from much earlier periods. However, the invention of the
telescope was required before astronomy was able to develop into a modern
science. Historically, astronomy has included disciplines as diverse as
astrometry, celestial navigation, observational astronomy, the making of
calendars, and even astrology, but professional astronomy is nowadays often
considered to be synonymous with astrophysics. Since the 20th century, the field
of professional astronomy split into observational and theoretical branches.
Observational astronomy is focused on acquiring and analyzing data, mainly using
basic principles of physics. Theoretical astronomy is oriented towards the
development of computer or analytical models to describe astronomical objects
and phenomena. The two fields complement each other, with theoretical astronomy
seeking to explain the observational results, and observations being used to
confirm theoretical results.
Amateur astronomers have contributed to many important astronomical discoveries,
and astronomy is one of the few sciences where amateurs can still play an active
role, especially in the discovery and observation of transient phenomena.
Old or even ancient astronomy is not to be confused with astrology, the belief
system that claims that human affairs are correlated with the positions of
celestial objects. Although the two fields share a common origin and a part of
their methods (namely, the use of ephemerides), they are distinct.
Lexicology
The word astronomy literally means "law of the stars" (or "culture of the stars"
depending on the translation) and is derived from the Greek αστρονομ?α,
astronomia, from the words ?στρον (astron, "star") and ν?μο? (nomos, "laws or
cultures").
Use of terms "astronomy" and "astrophysics"
Generally, either the term "astronomy" or "astrophysics" may be used to refer to
this subject. Based on strict dictionary definitions, "astronomy" refers to "the
study of objects and matter outside the earth's atmosphere and of their physical
and chemical properties" and "astrophysics" refers to the branch of astronomy
dealing with "the behavior, physical properties, and dynamic processes of
celestial objects and phenomena". In some cases, as in the introduction of the
introductory textbook The Physical Universe by Frank Shu, "astronomy" may be
used to describe the qualitative study of the subject, whereas "astrophysics" is
used to describe the physics-oriented version of the subject. However, since
most modern astronomical research deals with subjects related to physics, modern
astronomy could actually be called astrophysics. Various departments that
research this subject may use "astronomy" and "astrophysics", partly depending
on whether the department is historically affiliated with a physics department,
and many professional astronomers actually have physics degrees. Even the name
of the scientific journal Astronomy & Astrophysics reveals the ambiguity of the
use of the term.
History
History of astronomy
Further information: Archaeoastronomy
In early times, astronomy only comprised the observation and predictions of the
motions of objects visible to the naked eye. In some locations, such as
Stonehenge, early cultures assembled massive artifacts that likely had some
astronomical purpose. In addition to their ceremonial uses, these observatories
could be employed to determine the seasons, an important factor in knowing when
to plant crops, as well as in understanding the length of the year.
Before tools such as the telescope were invented early study of the stars had to
be conducted from the only vantage points available, namely tall buildings,
trees and high ground using the bare eye.
As civilizations developed, most notably in Mesopotamia, Ancient Greece, Egypt,
Persia, Maya, India, China, and the Islamic world, astronomical observatories
were assembled, and ideas on the nature of the universe began to be explored.
Most of early astronomy actually consisted of mapping the positions of the stars
and planets, a science now referred to as astrometry. From these observations,
early ideas about the motions of the planets were formed, and the nature of the
Sun, Moon and the Earth in the universe were explored philosophically. The Earth
was believed to be the center of the universe with the Sun, the Moon and the
stars rotating around it. This is known as the geocentric model of the universe.
A few notable astronomical discoveries were made prior to the application of the
telescope. For example, the obliquity of the ecliptic was estimated as early as
1000 BC by the Chinese. The Chaldeans discovered that lunar eclipses recurred in
a repeating cycle known as a saros. In the 2nd century BC, the size and distance
of the Moon were estimated by Hipparchus.
During the Middle Ages, observational astronomy was mostly stagnant in medieval
Europe, at least until the 13th century. However, observational astronomy
flourished in the Islamic world and other parts of the world. Some of the
prominent Arab Astronomers, who made significant contributions to the science
were Al-Battani and Thebit. Astronomers during that time introduced many Arabic
names that are now used for individual stars.
Scientific revolution
Galileo's sketches and observations of the Moon revealed that the surface was
mountainous
Galileo's sketches and observations of the Moon revealed that the surface was
mountainous
During the Renaissance, Nicolaus Copernicus proposed a heliocentric model of the
solar system. His work was defended, expanded upon, and corrected by Galileo
Galilei and Johannes Kepler. Galileo innovated by using telescopes to enhance
his observations.
Kepler was the first to devise a system that described correctly the details of
the motion of the planets with the Sun at the center. However, Kepler did not
succeed in formulating a theory behind the laws he wrote down. It was left to
Newton's invention of celestial dynamics and his law of gravitation to finally
explain the motions of the planets. Newton also developed the reflecting
telescope.
Further discoveries paralleled the improvements in the size and quality of the
telescope. More extensive star catalogues were produced by Lacaille. The
astronomer William Herschel made a detailed catalog of nebulosity and clusters,
and in 1781 discovered the planet Uranus, the first new planet found. The
distance to a star was first announced in 1838 when the parallax of 61 Cygni was
measured by Friedrich Bessel.
During the nineteenth century, attention to the three body problem by Euler,
Clairaut, and D'Alembert led to more accurate predictions about the motions of
the Moon and planets. This work was further refined by Lagrange and Laplace,
allowing the masses of the planets and moons to be estimated from their
perturbations.
Significant advances in astronomy came about with the introduction of new
technology, including the spectroscope and photography. Fraunhofer discovered
about 600 bands in the spectrum of the Sun in 1814-15, which, in 1859, Kirchhoff
ascribed to the presence of different elements. Stars were proven to be similar
to the Earth's own Sun, but with a wide range of temperatures, masses, and
sizes.
The existence of the Earth's galaxy, the Milky Way, as a separate group of
stars, was only proved 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. Modern astronomy has also discovered many
exotic objects such as quasars, pulsars, blazars, and radio galaxies, and has
used these observations to develop physical theories which describe some of
these objects in terms of equally exotic objects such as black holes and neutron
stars. Physical cosmology made huge advances during the 20th century, with the
model of the 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.
Observational astronomy
The Very Large Array in New Mexico, an example of a radio telescope.
The Very Large Array in New Mexico, an example of a radio telescope.
Observational astronomy
In astronomy, information is mainly received from the detection and analysis of
visible light or other regions of the electromagnetic radiation. Observational
astronomy may be divided according to the observed region of the electromagnetic
spectrum. Some parts of the spectrum can be observed from the Earth's surface,
while other parts are only observable from either high altitudes or space.
Specific information on these subfields is given below.
Radio astronomy
Radio astronomy studies radiation with wavelengths greater than approximately
one millimeter. Radio astronomy is different from most other forms of
observational astronomy in that the observed radio waves can be treated as waves
rather than as discrete photons. Hence, it is relatively easier to measure both
the amplitude and phase of radio waves, whereas this is not as easily done at
shorter wavelengths.
Though some radio waves are produced by astronomical objects in the form of
thermal emission, most of the radio emission that is observed from Earth is seen
in the form of synchrotron radiation, which is produced when electrons oscillate
around magnetic fields. Additionally, a number of spectral lines produced by
interstellar gas, particularly the hydrogen spectral line at 21 cm, are
observable at radio wavelengths.
A wide variety of objects are observable at radio wavelengths, including
supernovae, interstellar gas, pulsars, and active galactic nuclei.
Infrared astronomy
Infrared astronomy deals with the detection and analysis of infrared radiation
(wavelengths longer than red light). Except at wavelengths close to visible
light, infrared radiation is heavily absorbed by the atmosphere, and the
atmosphere produces significant infrared emission. Consequently, infrared
observatories have to be located in high, dry places or in space. Infrared
astronomy is particularly useful for observation of galactic regions cloaked by
dust, and for studies of molecular gases.
Optical astronomy
The Subaru Telescope (left) and Keck Observatory (center) on Mauna Kea, both
examples of an observatory that operates at near-infrared and visible
wavelengths. The NASA Infrared Telescope Facility (right) is an example of a
telescope that operates only at near-infrared wavelengths.
The Subaru Telescope (left) and Keck Observatory (center) on Mauna Kea, both
examples of an observatory that operates at near-infrared and visible
wavelengths. The NASA Infrared Telescope Facility (right) is an example of a
telescope that operates only at near-infrared wavelengths.
Historically, optical astronomy, also called visible light astronomy, is the
oldest form of astronomy. Optical images were originally drawn by hand. In the
late nineteenth century and most of the twentieth century, images were made
using photographic equipment. Modern images are made using digital detectors,
particularly detectors using charge-coupled devices (CCDs). Although visible
light itself extends from approximately 4000 ? to 7000 ? (400 nm to 700 nm), the
same equipment used at these wavelengths is also used to observe some
near-ultraviolet and near-infrared radiation.
Ultraviolet astronomy
Ultraviolet astronomy is generally used to refer to observations at ultraviolet
wavelengths between approximately 100 and 3200 ? (10 to 320 nm). Light at these
wavelengths is absorbed by the Earth's atmosphere, so observations at these
wavelengths must be performed from the upper atmosphere or from space.
Ultraviolet astronomy is best suited to the study of thermal radiation and
spectral emission lines from hot blue stars (O stars and B stars) that are very
bright in this wave band. This includes the blue stars in other galaxies, which
have been the targets of several ultraviolet surveys. Other objects commonly
observed in ultraviolet light include planetary nebulae, supernova remnants, and
active galactic nuclei. However, ultraviolet light is easily absorbed by
interstellar dust, and measurement of the ultraviolet light from objects need to
be corrected for extinction.
X-ray astronomy
X-ray astronomy is the study of astronomical objects at X-ray wavelengths.
Typically, objects emit X-ray radiation as synchrotron emission (produced by
electrons oscillating around magnetic field lines), thermal emission from thin
gases (called bremsstrahlung radiation) that is above 107 (10 million) kelvins,
and thermal emission from thick gases (called blackbody radiation) that are
above 107 Kelvin. Since X-rays are absorbed by the Earth's atmosphere, all X-ray
observations must be done from high-altitude balloons, rockets, or spacecraft.
Notable X-ray sources include X-ray binaries, pulsars, supernova remnants,
elliptical galaxies, clusters of galaxies, and active galactic nuclei.
Gamma-ray astronomy
Gamma ray astronomy is the study of astronomical objects at the shortest
wavelengths of the electromagnetic spectrum. Gamma rays may be observed directly
by satellites such as the Compton Gamma Ray Observatory or by specialized
telescopes called atmospheric Cherenkov telescopes. The Cherenkov telescopes do
not actually detect the gamma rays directly but instead detect the flashes of
visible light produced when gamma rays are absorbed by the Earth's atmosphere.
Most gamma-ray emitting sources are actually gamma-ray bursts, objects which
only produce gamma radiation for a few milliseconds to thousands of seconds
before fading away. Only 10% of gamma-ray sources are non-transient sources.
These steady gamma-ray emitters include pulsars, neutron stars, and black hole
candidates such as active galactic nuclei.
Fields of observational astronomy not based on the electromagnetic spectrum
Other than electromagnetic radiation, few things may be observed from the Earth
that originate from great distances.
In neutrino astronomy, astronomers use special underground facilities such as
SAGE, GALLEX, and Kamioka II/III for detecting neutrinos. These neutrinos
originate primarily from the Sun but also from supernovae.
Cosmic rays consisting of very high energy particles can be observed hitting the
Earth's atmosphere. Additionally, some future neutrino detectors will also be
sensitive to the neutrinos produced when cosmic rays hit the Earth's atmosphere.
A few gravitational wave observatories have been constructed, but gravitational
waves are extremely difficult to detect.
Planetary astronomy has benefited from direct observation in the form of
spacecraft and sample return missions. These include fly-by missions with remote
sensors; landing vehicles that can perform experiments on the surface materials;
impactors that allow remote sensing of buried material, and sample return
missions that allow direct, laboratory examination.
Astrometry and celestial mechanics
Main articles: Astrometry and Celestial mechanics
One of the oldest fields in astronomy, and in all of science, is the measurement
of the positions of celestial objects. Historically, accurate knowledge of the
positions of the Sun, Moon, planets and stars has been essential in celestial
navigation.
Careful measurement of the positions of the planets has led to a solid
understanding of gravitational perturbations, and an ability to determine past
and future positions of the planets with great accuracy, a field known as
celestial mechanics. More recently the tracking of near-Earth objects will allow
for predictions of close encounters, and potential collisions, with the Earth.
The measurement of stellar parallax of nearby stars provides a fundamental
baseline in the cosmic distance ladder that is used to measure the scale of the
universe. Parallax measurements of nearby stars provide an absolute baseline for
the properties of more distant stars, because their properties can be compared.
Measurements of radial velocity and proper motion show the kinematics of these
systems through the Milky Way galaxy. Astrometric results are also used to
measure the distribution of dark matter in the galaxy.
During the 1990s, the astrometric technique of measuring the stellar wobble was
used to detect large extrasolar planets orbiting nearby stars.
Theoretical astronomy
Nucleosynthesis
* Stellar nucleosynthesis
* Big Bang nucleosynthesis
* Supernova nucleosynthesis
* Cosmic ray spallation
Related topics
* Astrophysics
* Nuclear fusion
o R-process
o S-process
* Nuclear fission
edit
Theoretical astronomers use a wide variety of tools which include analytical
models (for example, polytropes to approximate the behaviors of a star) and
computational numerical simulations. Each has some advantages. Analytical models
of a process are generally better for giving insight into the heart of what is
going on. Numerical models can reveal the existence of phenomena and effects
that would otherwise not be seen.
Theorists in astronomy endeavor to create theoretical models and figure out the
observational consequences of those models. This helps allow observers to look
for data that can refute a model or help in choosing between several alternate
or conflicting models.
Theorists also try to generate or modify models to take into account new data.
In the case of an inconsistency, the general tendency is to try to make minimal
modifications to the model to fit the data. In some cases, a large amount of
inconsistent data over time may lead to total abandonment of a model.
Topics studied by theoretical astronomers include: stellar dynamics and
evolution; galaxy formation; large-scale structure of matter in the Universe;
origin of cosmic rays; general relativity and physical cosmology, including
string cosmology and astroparticle physics. Astrophysical relativity serves as a
tool to gauge the properties of large scale structures for which gravitation
plays a significant role in physical phenomena investigated and as the basis for
black hole (astro)physics and the study of gravitational waves.
Some widely accepted and studied theories and models in astronomy, now included
in the Lambda-CDM model are the Big Bang, Cosmic inflation, dark matter, and
fundamental theories of physics.
A few examples of this process:
Physical process Experimental tool Theoretical model Explains/predicts
Gravitation Radio telescopes Self-gravitating system Emergence of a star system
Nuclear fusion Spectroscopy Stellar evolution How the stars shine and how metals
formed
The Big Bang Hubble Space Telescope, COBE Expanding universe Age of the Universe
Quantum fluctuations Cosmic inflation Flatness problem
Gravitational collapse X-ray astronomy General relativity Black holes at the
center of Andromeda galaxy
CNO cycle in stars
Dark matter and dark energy are the current leading topics in astronomy, as
their discovery and controversy originated during the study of the galaxies.
Subfield of astronomy for specific astronomical objects
Solar astronomy
Sun
The most frequently studied star is the Sun, a typical main-sequence dwarf star
of stellar class G2 V, and about 4.6 Gyr in age. The Sun is not considered a
variable star, but it does undergo periodic changes in activity known as the
sunspot cycle. This is an 11-year fluctuation in sunspot numbers. Sunspots are
regions of lower-than- average temperatures that are associated with intense
magnetic activity.
An ultraviolet image of the Sun's active photosphere as viewed by the TRACE
space telescope. NASA photo.
An ultraviolet image of the Sun's active photosphere as viewed by the TRACE
space telescope. NASA photo.
The Sun has steadily increased in luminosity over the course of its life,
increasing by 40% since it first became a main-sequence star. The Sun has also
undergone periodic changes in luminosity that can have a significant impact on
the Earth. The Maunder minimum, for example, is believed to have caused the
Little Ice Age phenomenon during the Middle Ages.
The visible outer surface of the Sun is called the photosphere. Above this layer
is a thin region known as the chromosphere. This is surrounded by a transition
region of rapidly increasing temperatures, then by the super-heated corona.
At the center of the Sun is the core region, a volume of sufficient temperature
and pressure for nuclear fusion to occur. Above the core is the radiation zone,
where the plasma conveys the energy flux by means of radiation. The outer layers
form a convection zone where the gas material transports energy primarily
through physical displacement of the gas. It is believed that this convection
zone creates the magnetic activity that generates sun spots.
A solar wind of plasma particles constantly streams outward from the Sun until
it reaches the heliopause. This solar wind interacts with the magnetosphere of
the Earth to create the Van Allen radiation belts, as well as the aurora where
the lines of the Earth's magnetic field descend into the atmosphere.
Planetary science
Main articles: Planetary science and Planetary geology
This astronomical field examines the assemblage of planets, moons, dwarf
planets, comets, asteroids, and other bodies orbiting the Sun, as well as
extrasolar planets. The solar system has been relatively well-studied, initially
through telescopes and then later by spacecraft. This has provided a good
overall understanding of the formation and evolution of this planetary system,
although many new discoveries are still being made.
The black spot at the top is a dust devil climbing a crater wall on Mars. This
moving, swirling column of Martian atmosphere (comparable to a terrestrial
tornado) created the long, dark streak. NASA image.
The black spot at the top is a dust devil climbing a crater wall on Mars. This
moving, swirling column of Martian atmosphere (comparable to a terrestrial
tornado) created the long, dark streak. NASA image.
The solar system is subdivided into the inner planets, the asteroid belt, and
the outer planets. The inner terrestrial planets consist of Mercury, Venus,
Earth, and Mars. The outer gas giant planets are Jupiter, Saturn, Uranus and
Neptune. Beyond Neptune lie the Kuiper Belt, and finally the Oort Cloud, which
may extend as far as a light-year.
The planets were formed by a protoplanetary disk that surrounded the early Sun.
Through a process that included gravitational attraction, collision, and
accretion, the disk formed clumps of matter that, with time, became
protoplanets. The radiation pressure of the solar wind then expelled most of the
unaccreted matter, and only those planets with sufficient mass retained their
gaseous atmosphere. The planets continued to sweep up, or eject, the remaining
matter during a period of intense bombardment, evidenced by the many impact
craters on the Moon. During this period, some of the protoplanets may have
collided, the leading hypothesis for how the Moon was formed.
Once a planet reaches sufficient mass, the materials with different densities
segregate within, during planetary differentiation. This process can form a
stony or metallic core, surrounded by a mantle and an outer surface. The core
may include solid and liquid regions, and some planetary cores generate their
own magnetic field, which can protect their atmospheres from solar wind
stripping.
A planet or moon's interior heat is produced from the collisions that created
the body, radioactive materials (e.g. uranium, thorium, and 26Al), or tidal
heating. Some planets and moons accumulate enough heat to drive geologic
processes such as volcanism and tectonics. Those that accumulate or retain an
atmosphere can also undergo surface erosion from wind or water. Smaller bodies,
without tidal heating, cool more quickly; and their geological activity ceases
with the exception of impact cratering.
Stellar astronomy
The Ant planetary nebula. Ejecting gas from the dying central star shows
symmetrical patterns unlike the chaotic patterns of ordinary explosions.
The Ant planetary nebula. Ejecting gas from the dying central star shows
symmetrical patterns unlike the chaotic patterns of ordinary explosions.
Star
The study of stars and stellar evolution is fundamental to our understanding of
the universe. The astrophysics of stars has been determined through observation
and theoretical understanding; and from computer simulations of the interior.
Star formation occurs in dense regions of dust and gas, known as giant molecular
clouds. When destabilized, cloud fragments can collapse under the influence of
gravity, to form a protostar. A sufficiently dense, and hot, core region will
trigger nuclear fusion, thus creating a main-sequence star.
Almost all elements heavier than hydrogen and helium were created inside the
cores of stars.
The characteristics of the resulting star depend primarily upon its starting
mass. The more massive the star, the greater its luminosity, and the more
rapidly it expends the hydrogen fuel in its core. Over time, this hydrogen fuel
is completely converted into helium, and the star begins to evolve. The fusion
of helium requires a higher core temperature, so that the star both expands in
size, and increases in core density. The resulting red giant enjoys a brief life
span, before the helium fuel is in turn consumed. Very massive stars can also
undergo a series of decreasing evolutionary phases, as they fuse increasingly
heavier elements.
The final fate of the star depends on its mass, with stars of mass greater than
about eight times the Sun becoming core collapse supernovae; while smaller stars
form planetary nebulae, and evolve into white dwarfs. The remnant of a supernova
is a dense neutron star, or, if the stellar mass was at least three times that
of the Sun, a black hole. Close binary stars can follow more complex
evolutionary paths, such as mass transfer onto a white dwarf companion that can
potentially cause a supernova. Planetary nebulae and supernovae are necessary
for the distribution of metals to the interstellar medium; without them, all new
stars (and their planetary systems) would be formed from hydrogen and helium
alone.
Galactic astronomy
Galactic astronomy
Observed structure of the Milky Way's spiral arms
Observed structure of the Milky Way's spiral arms
Our solar system orbits within the Milky Way, a barred spiral galaxy that is a
prominent member of the Local Group of galaxies. It is a rotating mass of gas,
dust, stars and other objects, held together by mutual gravitational attraction.
As the Earth is located within the dusty outer arms, there are large portions of
the Milky Way that are obscured from view.
In the center of the Milky Way is the core, a bar-shaped bulge with what is
believed to be a supermassive black hole at the center. This is surrounded by
four primary arms that spiral from the core. This is a region of active star
formation that contains many younger, population II stars. The disk is
surrounded by a spheroid halo of older, population I stars, as well as
relatively dense concentrations of stars known as globular clusters.
Between the stars lies the interstellar medium, a region of sparse matter. In
the densest regions, molecular clouds of molecular hydrogen and other elements
create star-forming regions. These begin as irregular dark nebulae, which
concentrate and collapse (in volumes determined by the Jeans length) to form
compact protostars.
As the more massive stars appear, they transform the cloud into an H II region
of glowing gas and plasma. The stellar wind and supernova explosions from these
stars eventually serve to disperse the cloud, often leaving behind one or more
young open clusters of stars. These clusters gradually disperse, and the stars
join the population of the Milky Way.
Kinematic studies of matter in the Milky Way and other galaxies have
demonstrated that there is more mass than can be accounted for by visible
matter. A dark matter halo appears to dominate the mass, although the nature of
this dark matter remains undetermined.
Extragalactic astronomy
Extragalactic astronomy
The study of objects outside of our galaxy is a branch of astronomy concerned
with the formation and evolution of Galaxies; their morphology and
classification; and the examination of active galaxies, and the groups and
clusters of galaxies. The latter is important for the understanding of the
large-scale structure of the cosmos.
This image shows several blue, loop-shaped objects that are multiple images of
the same galaxy, duplicated by the gravitational lens effect of the cluster of
yellow galaxies near the middle of the photograph. The lens is produced by the
cluster's gravitational field that bends light to magnify and distort the image
of a more distant object.
This image shows several blue, loop-shaped objects that are multiple images of
the same galaxy, duplicated by the gravitational lens effect of the cluster of
yellow galaxies near the middle of the photograph. The lens is produced by the
cluster's gravitational field that bends light to magnify and distort the image
of a more distant object.
Most galaxies are organized into distinct shapes that allow for classification
schemes. They are commonly divided into spiral, elliptical and Irregular
galaxies.
As the name suggests, an elliptical galaxy has the cross-sectional shape of an
ellipse. The stars move along random orbits with no preferred direction. These
galaxies contain little or no interstellar dust; few star-forming regions; and
generally older stars. Elliptical galaxies are more commonly found at the core
of galactic clusters, and may be formed through mergers of large galaxies.
A spiral galaxy is organized into a flat, rotating disk, usually with a
prominent bulge or bar at the center, and trailing bright arms that spiral
outward. The arms are dusty regions of star formation where massive young stars
produce a blue tint. Spiral galaxies are typically surrounded by a halo of older
stars. Both the Milky Way and the Andromeda Galaxy are spiral galaxies.
Irregular galaxies are chaotic in appearance, and are neither spiral nor
elliptical. About a quarter of all galaxies are irregular, and the peculiar
shapes of such galaxies may be the result of gravitational interaction.
An active galaxy is a formation that is emitting a significant amount of its
energy from a source other than stars, dust and gas; and is powered by a compact
region at the core, usually thought to be a super-massive black hole that is
emitting radiation from in-falling material.
A radio galaxy is an active galaxy that is very luminous in the radio portion of
the spectrum, and is emitting immense plumes or lobes of gas. Active galaxies
that emit high-energy radiation include Seyfert galaxies, Quasars, and Blazars.
Quasars are believed to be the most consistently luminous objects in the known
universe.
The large-scale structure of the cosmos is represented by groups and clusters of
galaxies. This structure is organized in a hierarchy of groupings, with the
largest being the superclusters. The collective matter is formed into filaments
and walls, leaving large voids in between.
Cosmology
Physical cosmology
Cosmology (from the Greek κοσμο? "world, universe" and λογο? "word, study")
could be considered the study of the universe as a whole.
Observations of the large-scale structure of the universe, a branch known as
physical cosmology, have provided a deep understanding of the formation and
evolution of the cosmos. Fundamental to modern cosmology is the well-accepted
theory of the big bang, wherein our universe began at a single point in time,
and thereafter expanded over the course of 13.7 Gyr to its present condition.
The concept of the big bang can be traced back to the discovery of the microwave
background radiation in 1965.
In the course of this expansion, the universe underwent several evolutionary
stages. In the very early moments, it is theorized that the universe experienced
a very rapid cosmic inflation, which homogenized the starting conditions.
Thereafter, nucleosynthesis produced the elemental abundance of the early
universe. (See also nucleocosmochronology.)
When the first atoms formed, space became transparent to radiation, releasing
the energy viewed today as the microwave background radiation. The expanding
universe then underwent a Dark Age due to the lack of stellar energy sources.
A hierarchical structure of matter began to form from minute variations in the
mass density. Matter accumulated in the densest regions, forming clouds of gas
and the earliest stars. These massive stars triggered the reionization process
and are believed to have created many of the heavy elements in the early
universe.
Gravitational aggregations clustered into filaments, leaving voids in the gaps.
Gradually, organizations of gas and dust merged to form the first primitive
galaxies. Over time, these pulled in more matter, and were often organized into
groups and clusters of galaxies, then into larger-scale superclusters.
Fundamental to the structure of the universe is the existence of dark matter and
dark energy. These are now thought to be the dominant components, forming 96% of
the density of the universe. For this reason, much effort is expended in trying
to understand the physics of these components.
Interdisciplinary studies
Astronomy and astrophysics have developed significant interdisciplinary links
with other major scientific fields. These include:
* Astrobiology: the study of the advent and evolution of biological systems in
the universe.
* Archaeoastronomy: the study of ancient or traditional astronomies in their
cultural context, utilizing archaeological and anthropological evidence.
* Astrochemistry: the study of the chemicals found in space, usually in
molecular clouds, and their formation, interaction and destruction. It
represents an overlap of the disciplines of astronomy and chemistry.
* Cosmochemistry: the study of the chemicals found within the Solar System,
including the origins of the elements and variations in the isotope ratios.
Amateur astronomy
Amateur astronomy
Amateur astronomers can build their own equipment, and can hold star parties and
gatherings, such as Stellafane.
Amateur astronomers can build their own equipment, and can hold star parties and
gatherings, such as Stellafane.
Collectively, amateur astronomers observe a variety of celestial objects and
phenomena sometimes with equipment that they build themselves. Common targets of
amateur astronomers include the Moon, planets, stars, comets, meteor showers,
and a variety of deep-sky objects such as star clusters, galaxies, and nebulae.
One branch of amateur astronomy, amateur astrophotography, involves the taking
of photos of the night sky. Many amateurs like to specialize in the observation
of particular objects, types of objects, or types of events which interest them.
Most amateurs work at visible wavelengths, but a small minority experiment with
wavelengths outside the visible spectrum. This includes the use of infrared
filters on conventional telescopes, and also the use of radio telescopes. The
pioneer of amateur radio astronomy was Karl Jansky who started observing the sky
at radio wavelengths in the 1930s. A number of amateur astronomers use either
homemade telescopes or use radio telescopes which were originally built for
astronomy research but which are now available to amateurs (e.g. the One-Mile
Telescope).
Amateur astronomers continue to make scientific contributions to the field of
astronomy. Indeed, it is one of the few scientific disciplines where amateurs
can still make significant contributions. Amateurs can make occultation
measurements that are used to refine the orbits of minor planets. They can also
discover comets, and perform regular observations of variable stars.
Improvements in digital technology have allowed amateurs to make impressive
advances in the field of astrophotography.
Major questions in astronomy
See also: Unsolved problems in physics
Although the scientific discipline of astronomy has made tremendous strides in
understanding the nature of the universe and its contents, there remain some
important unanswered questions. Answers to these may require the construction of
new ground- and space-based instruments, and possibly new developments in
theoretical and experimental physics.
* What is the origin of the stellar mass spectrum? That is, why do astronomers
observe the same distribution of stellar masses—the initial mass
function—apparently regardless of the initial conditions? A deeper understanding
of the formation of stars and planets is needed.
* Is there other life in the Universe? Especially, is there other intelligent
life? If so, what is the explanation for the Fermi paradox? The existence of
life elsewhere has important scientific and philosophical implications.
* What is the nature of dark matter and dark energy? These dominate the
evolution and fate of the cosmos, yet we are still uncertain about their true
natures.
* Why did the universe come to be? Why, for example, are the physical constants
so finely tuned that they permit the existence of life? Could they be the result
of cosmological natural selection? What caused the cosmic inflation that
produced our homogeneous universe?
* What will be the ultimate fate of the universe?
Are you interested in
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RuneScape is set in a medieval fantasy world, similar to "Guild Wars" or
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with most massive multiplayer online roleplaying games (MMORPG), there is no
overall objective or end to the game. Players explore, form alliances, perform
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RuneScape has often been one of
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unique game, comes unique players. Players get bored, and then try to develop
cheats....autos or bots that will help them achieve success in their beloved
games of Runescape 2.
RuneScape is a virtual world which
is divided into two part: Members Areas and Non-Members areas. People who pay to
play (p2p), receive access to the special areas. They also have access to the
free areas. The members' places are much larger, offer "better" items for the
gameplay of rs2, and much, much more. The character that you create when you
first start playing runescape, moves around the game on foot; either by running,
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2 is an RPG (Role playing game), there is no set path a person must take to play
rs. They can choose what to do, and when, whether it be training their
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runescape 2 based site. They have now, however, taken another look....
Of course the king of all game
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trick
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The master of massive multiplayer
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Trik.com; this site is one of the best today. The forum section,
Trik.com forum, originally came from IJFG.com (Internet Junction For
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set in a medieval fantasy world, similar to "Guild Wars" or "EverQuest," where
players control character representations of themselves. As with most MMORPG,
there is no overall objective or end to the game. Players explore, form
alliances, perform optional tasks, and complete quests for rewards and to build
characters' skills.
Trik.com continues IJFG.com's
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With the rising popularity of
commercial MMORPG games came the desire from ardent players of these games to
run their own servers beside the ones run by the game's creator. Since the
original server software is not usually available, the behavior of the server
has to be re-engineered. This can be done by analyzing the data stream with the
original server, or by disassembling and analyzing the client which is
available.
Ultima Online was one of the first
large MMORPGs. Due to its openness in implementation, server emulators arose
very quickly, even during the beta stage of development. The destination to
which the client connects was changeable by simply editing a text file. In beta
stage the client-server data stream was not encrypted yet. The term server
emulator became known through Ultima Online server reimplementation such as UOX,
which was the pioneer. Many forks and reimplementations followed UOX, because
its source code was released under the GNU General Public License relatively
early. RunUO is today the most widely used UO-server emulator. After RuneScape
implemented anti-cheating measures, many gamers left and started their own
private servers. The best place to discuss the private server is at
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Another useful site is
Rune
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A defining moment in internet
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