Astronomy
Astronomy is a
Astronomy is one of the oldest natural sciences. The early civilizations in
Professional astronomy is split into observational and theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects. This data is then analyzed using basic principles of physics. Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. These two fields complement each other. Theoretical astronomy seeks to explain observational results and observations are used to confirm theoretical results.
Astronomy is one of the few sciences in which amateurs play an
Etymology
Astronomy (from the Greek ἀστρονομία from ἄστρον astron, "star" and -νομία -nomia from νόμος nomos, "law" or "culture") means "law of the stars" (or "culture of the stars" depending on the translation). Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects.[2] Although the two fields share a common origin, they are now entirely distinct.[3]
Use of terms "astronomy" and "astrophysics"
"Astronomy" and "astrophysics" are synonyms.[4][5][6] 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",[7] while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, and dynamic processes of celestial objects and phenomena".[8] 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.[9] However, since most modern astronomical research deals with subjects related to physics, modern astronomy could actually be called astrophysics.[4] Some fields, such as astrometry, are purely astronomy rather than also astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics", partly depending on whether the department is historically affiliated with a physics department,[5] and many professional astronomers have physics rather than astronomy degrees.[6] Some titles of the leading scientific journals in this field include The Astronomical Journal, The Astrophysical Journal, and Astronomy & Astrophysics.
History
Ancient times
In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye. In some locations, early cultures assembled massive artifacts that may have 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 and in understanding the length of the year.[10]
Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye. As civilizations developed, most notably in
A particularly important early development was the beginning of mathematical and scientific astronomy, which began among
Following the Babylonians, significant advances in astronomy were made in
Middle Ages
Medieval Europe housed a number of important astronomers.
It is also believed that the ruins at
For over six centuries (from the recovery of ancient learning during the late Middle Ages into the Enlightenment), the
Scientific revolution
During the
Improvements in the size and quality of the telescope led to further discoveries. The English astronomer
During the 18–19th centuries, the study of the
Significant advances in astronomy came about with the introduction of new technology, including the
The existence of the Earth's galaxy, the
Observational astronomy
The main source of information about
Radio astronomy
Radio astronomy uses radiation with wavelengths greater than approximately one millimeter, outside the visible range.[47] 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.[47]
Although some
A wide variety of other objects are observable at radio wavelengths, including
Infrared astronomy
Infrared astronomy is founded on the detection and analysis of
With the exception of infraredOptical astronomy
Historically, optical astronomy, also called visible light astronomy, is the oldest form of astronomy.
Ultraviolet astronomy
Ultraviolet astronomy employs
X-ray astronomy
X-ray astronomy uses
Gamma-ray astronomy
Gamma ray astronomy observes astronomical objects at the shortest wavelengths of the electromagnetic spectrum. Gamma rays may be observed directly by satellites such as the
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.[47]
Fields not based on the electromagnetic spectrum
In addition to electromagnetic radiation, a few other events originating from great distances may be observed from the Earth.
In
The combination of observations made using electromagnetic radiation, neutrinos or gravitational waves and other complementary information, is known as multi-messenger astronomy.[59][60]
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 (the use of celestial objects to guide navigation) and in the making of calendars.[61]: 39
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 or potential collisions of the Earth with those objects.[62]
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, as their properties can be compared. Measurements of the radial velocity and proper motion of stars allow astronomers to plot the movement of these systems through the Milky Way galaxy. Astrometric results are the basis used to calculate the distribution of speculated dark matter in the galaxy.[63]
During the 1990s, the measurement of the
Theoretical astronomy
Nucleosynthesis |
---|
Related topics |
Theoretical astronomers use several tools including analytical models and computational numerical simulations; each has its particular advantages. Analytical models of a process are better for giving broader insight into the heart of what is going on. Numerical models reveal the existence of phenomena and effects otherwise unobserved.[65][66]
Theorists in astronomy endeavor to create theoretical models that are based on existing observations and known physics, and to predict observational consequences of those models. The observation of phenomena predicted by a model allows astronomers to select between several alternative or conflicting models. Theorists also modify existing models to take into account new observations. In some cases, a large amount of observational data that is inconsistent with a model may lead to abandoning it largely or completely, as for
Phenomena modeled by theoretical astronomers include:
- stellar dynamics and evolution
- galaxy formation
- large-scale distribution of matter in the Universe
- the origin of cosmic rays
- general relativity and physical cosmology, including string cosmology and astroparticle physics.
Modern theoretical astronomy reflects dramatic advances in observation since the 1990s, including studies of the
Specific subfields
Astrophysics
Astrophysics is the branch of astronomy that employs the principles of physics and
In practice, modern astronomical research often involves a substantial amount of work in the realms of
Astrochemistry
Astrochemistry is the study of the abundance and reactions of
Astrobiology
Astrobiology is an interdisciplinary scientific field concerned with the origins, early evolution, distribution, and future of life in the universe. Astrobiology considers the question of whether extraterrestrial life exists, and how humans can detect it if it does.[73] The term exobiology is similar.[74]
Astrobiology makes use of
This
Physical cosmology
billion years ago ) |
Cosmology (from the Greek κόσμος (kosmos) "world, universe" and λόγος (logos) "word, study" or literally "logic") could be considered the study of the Universe as a whole.
Observations of the
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
When the first neutral atoms formed from a sea of primordial ions, 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.[82]
A hierarchical structure of matter began to form from minute variations in the mass density of space. Matter accumulated in the densest regions, forming clouds of gas and the earliest stars, the
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.[84]
Fundamental to the structure of the Universe is the existence of dark matter and dark energy. These are now thought to be its dominant components, forming 96% of the mass of the Universe. For this reason, much effort is expended in trying to understand the physics of these components.[85]
Extragalactic astronomy
The study of objects outside our galaxy is a branch of astronomy concerned with the
Most galaxies are organized into distinct shapes that allow for classification schemes. They are commonly divided into spiral, elliptical and Irregular galaxies.[86]
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 older stars.[61]: 877–878 Elliptical galaxies may have been formed by other galaxies merging.[61]: 939
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 within which massive young stars produce a blue tint. Spiral galaxies are typically surrounded by a halo of older stars. Both the Milky Way and one of our nearest galaxy neighbors, the Andromeda Galaxy, are spiral galaxies.[61]: 875
Irregular galaxies are chaotic in appearance, and are neither spiral nor elliptical.[61]: 879 About a quarter of all galaxies are irregular, and the peculiar shapes of such galaxies may be the result of gravitational interaction.[87]
An active galaxy is a formation that emits a significant amount of its energy from a source other than its stars, dust and gas. It is powered by a compact region at the core, thought to be a supermassive black hole that is emitting radiation from in-falling material.[61]: 907 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 shorter frequency, high-energy radiation include Seyfert galaxies, quasars, and blazars. Quasars are believed to be the most consistently luminous objects in the known universe.[88]
The
Galactic astronomy
The 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.[61]: 837–842, 944
In the center of the Milky Way is the core, a bar-shaped bulge with what is believed to be a
Between the stars lies the
As the more massive stars appear, they transform the cloud into an H II region (ionized atomic hydrogen) of glowing gas and plasma. The stellar wind and supernova explosions from these stars eventually cause the cloud to disperse, 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.[92]
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.[93]
Stellar astronomy
The study of stars and
Almost all elements heavier than hydrogen and helium were created inside the cores of stars.[94]
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 fuses its hydrogen fuel into helium 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. A star with a high enough core temperature will push its outer layers outward while increasing its core density. The resulting red giant formed by the expanding outer layers enjoys a brief life span, before the helium fuel in the core is in turn consumed. Very massive stars can also undergo a series of evolutionary phases, as they fuse increasingly heavier elements.[95]
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;[96] while smaller stars blow off their outer layers and leave behind the inert core in the form of a white dwarf. The ejection of the outer layers forms a planetary nebula.[97] 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.[98] Closely orbiting binary stars can follow more complex evolutionary paths, such as mass transfer onto a white dwarf companion that can potentially cause a supernova.[99] Planetary nebulae and supernovae distribute the "metals" produced in the star by fusion to the interstellar medium; without them, all new stars (and their planetary systems) would be formed from hydrogen and helium alone.[100]
Solar astronomy
At a distance of about eight light-minutes, the most frequently studied star is the
The Sun has steadily increased in luminosity 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.
At the center of the Sun is the core region, a volume of sufficient temperature and pressure for
A solar wind of plasma particles constantly streams outward from the Sun until, at the outermost limit of the Solar System, it reaches the
Planetary science
Planetary science is the study of 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 the Sun's planetary system, although many new discoveries are still being made.[105]
The Solar System is divided into the
The planets were formed 4.6 billion years ago in the
Once a planet reaches sufficient mass, the materials of different densities segregate within, during planetary differentiation. This process can form a stony or metallic core, surrounded by a mantle and an outer crust. 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.[108]
A planet or moon's interior heat is produced from the collisions that created the body, by the decay of radioactive materials (e.g.
Interdisciplinary studies
Astronomy and astrophysics have developed significant interdisciplinary links with other major scientific fields. Archaeoastronomy is the study of ancient or traditional astronomies in their cultural context, utilizing archaeological and anthropological evidence. Astrobiology is the study of the advent and evolution of biological systems in the Universe, with particular emphasis on the possibility of non-terrestrial life. Astrostatistics is the application of statistics to astrophysics to the analysis of a vast amount of observational astrophysical data.[110]
The study of
Amateur astronomy
Astronomy is one of the sciences to which amateurs can contribute the most.[114]
Collectively, amateur astronomers observe a variety of celestial objects and phenomena sometimes with consumer-level equipment or equipment that they build themselves. Common targets of amateur astronomers include the Sun, the Moon, planets, stars, comets, meteor showers, and a variety of deep-sky objects such as star clusters, galaxies, and nebulae. Astronomy clubs are located throughout the world and many have programs to help their members set up and complete observational programs including those to observe all the objects in the Messier (110 objects) or Herschel 400 catalogues of points of interest in the night sky. One branch of amateur astronomy, 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 that interest them.[115][116]
Most amateurs work at visible wavelengths, but many 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).[117][118]
Amateur astronomers continue to make scientific contributions to the field of astronomy and 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.[119][120][121]
Unsolved problems in astronomy
In the 21st century there remain important unanswered questions in astronomy. Some are cosmic in scope: for example, what are dark matter and dark energy? These dominate the evolution and fate of the cosmos, yet their true nature remains unknown.[122] What will be the ultimate fate of the universe?[123] Why is the abundance of lithium in the cosmos four times lower than predicted by the standard Big Bang model?[124] Others pertain to more specific classes of phenomena. For example, is the Solar System normal or atypical?[125] 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?[126] Likewise, questions remain about the formation of the first galaxies,[127] the origin of supermassive black holes,[128] the source of ultra-high-energy cosmic rays,[129] and more.
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.[130][131]
See also
- Cosmogony – Branch of science or a theory concerning the origin of the universe
- Outline of astronomy
- Outline of space science – Overview of and topical guide to space science
- Space exploration – Exploration of space, planets, and moons
Lists
- Glossary of astronomy – List of definitions of terms and concepts commonly used in the study of astronomy
- List of astronomical instruments
- List of astronomical observatories
- List of astronomy acronyms
- List of software for astronomy research and education
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This poses a challenge to these models, because [...]
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{{cite web}}
: CS1 maint: unfit URL (link) - ^ Sagan, Carl. "The Quest for Extraterrestrial Intelligence". Cosmic Search Magazine. Archived from the original on 18 August 2006. Retrieved 12 August 2006.
Bibliography
- Newcomb, Simon; Clerke, Agnes Mary (1911). . Encyclopædia Britannica. Vol. 2 (11th ed.). pp. 800–819.
- Harpaz, Amos (1994). Stellar Evolution. A K Peters, Ltd. ISBN 978-1-56881-012-6.
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- James, C. Renée (2023). Things That Go Bump in the Universe: How Astronomers Decode Cosmic Chaos. Johns Hopkins University Press. ISBN 978-1421446936. Archivedfrom the original on 13 December 2023.
External links
- NASA/IPAC Extragalactic Database (NED) (NED-Distances)
- Core books and Core journals in Astronomy, from the Smithsonian/NASA Astrophysics Data System