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Astronomy applies the concepts from physics, biology, and geology to explain their origin and evolution. We can divide astronomy into 4 sub-fields: ASTROPHYSICS: Applying the laws of physics in space; ASTROMETRY: Mapping celestial bodies; ASTROGEOLOGY: Examining rocks, terrain, and material in space; ASTROBIOLOGY: Searching for life outside Earth
- Overview
- The scope of astronomy
- Determining astronomical distances
Astronomy is the study of objects and phenomena beyond Earth. Astronomers study objects as close as the Moon and the rest of the solar system through the stars of the Milky Way Galaxy and out to distant galaxies billions of light-years away.
How is astronomy different from cosmology?
Astronomy is the study of objects and phenomena beyond Earth, whereas cosmology is a branch of astronomy that studies the origin of the universe and how it has evolved. For example, the big bang, the origin of the chemical elements, and the cosmic microwave background are all subjects of cosmology. However, other subjects such as extrasolar planets and stars in the present Milky Way Galaxy are not.
astronomy, science that encompasses the study of all extraterrestrial objects and phenomena. Until the invention of the telescope and the discovery of the laws of motion and gravity in the 17th century, astronomy was primarily concerned with noting and predicting the positions of the Sun, Moon, and planets, originally for calendrical and astrological purposes and later for navigational uses and scientific interest. The catalog of objects now studied is much broader and includes, in order of increasing distance, the solar system, the stars that make up the Milky Way Galaxy, and other, more distant galaxies. With the advent of scientific space probes, Earth also has come to be studied as one of the planets, though its more-detailed investigation remains the domain of the Earth sciences.
Since the late 19th century, astronomy has expanded to include astrophysics, the application of physical and chemical knowledge to an understanding of the nature of celestial objects and the physical processes that control their formation, evolution, and emission of radiation. In addition, the gases and dust particles around and between the stars have become the subjects of much research. Study of the nuclear reactions that provide the energy radiated by stars has shown how the diversity of atoms found in nature can be derived from a universe that, following the first few minutes of its existence, consisted only of hydrogen, helium, and a trace of lithium. Concerned with phenomena on the largest scale is cosmology, the study of the evolution of the universe. Astrophysics has transformed cosmology from a purely speculative activity to a modern science capable of predictions that can be tested.
Its great advances notwithstanding, astronomy is still subject to a major constraint: it is inherently an observational rather than an experimental science. Almost all measurements must be performed at great distances from the objects of interest, with no control over such quantities as their temperature, pressure, or chemical composition. There are a few exceptions to this limitation—namely, meteorites (most of which are from the asteroid belt, though some are from the Moon or Mars), rock and soil samples brought back from the Moon, samples of comet and asteroid dust returned by robotic spacecraft, and interplanetary dust particles collected in or above the stratosphere. These can be examined with laboratory techniques to provide information that cannot be obtained in any other way. In the future, space missions may return surface materials from Mars, or other objects, but much of astronomy appears otherwise confined to Earth-based observations augmented by observations from orbiting satellites and long-range space probes and supplemented by theory.
A central undertaking in astronomy is the determination of distances. Without a knowledge of astronomical distances, the size of an observed object in space would remain nothing more than an angular diameter and the brightness of a star could not be converted into its true radiated power, or luminosity. Astronomical distance measurement began with a knowledge of Earth’s diameter, which provided a base for triangulation. Within the inner solar system, some distances can now be better determined through the timing of radar reflections or, in the case of the Moon, through laser ranging. For the outer planets, triangulation is still used. Beyond the solar system, distances to the closest stars are determined through triangulation, in which the diameter of Earth’s orbit serves as the baseline and shifts in stellar parallax are the measured quantities. Stellar distances are commonly expressed by astronomers in parsecs (pc), kiloparsecs, or megaparsecs. (1 pc = 3.086 × 1018 cm, or about 3.26 light-years [1.92 × 1013 miles].) Distances can be measured out to around a kiloparsec by trigonometric parallax (see star: Determining stellar distances). The accuracy of measurements made from Earth’s surface is limited by atmospheric effects, but measurements made from the Hipparcos satellite in the 1990s extended the scale to stars as far as 650 parsecs, with an accuracy of about a thousandth of an arc second. The Gaia satellite is expected to measure stars as far away as 10 kiloparsecs to an accuracy of 20 percent. Less-direct measurements must be used for more-distant stars and for galaxies.
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Two general methods for determining galactic distances are described here. In the first, a clearly identifiable type of star is used as a reference standard because its luminosity has been well determined. This requires observation of such stars that are close enough to Earth that their distances and luminosities have been reliably measured. Such a star is termed a “standard candle.” Examples are Cepheid variables, whose brightness varies periodically in well-documented ways, and certain types of supernova explosions that have enormous brilliance and can thus be seen out to very great distances. Once the luminosities of such nearer standard candles have been calibrated, the distance to a farther standard candle can be calculated from its calibrated luminosity and its actual measured intensity. (The measured intensity [I] is related to the luminosity [L] and distance [d] by the formula I = L/4πd2.) A standard candle can be identified by means of its spectrum or the pattern of regular variations in brightness. (Corrections may have to be made for the absorption of starlight by interstellar gas and dust over great distances.) This method forms the basis of measurements of distances to the closest galaxies.
The second method for galactic distance measurements makes use of the observation that the distances to galaxies generally correlate with the speeds with which those galaxies are receding from Earth (as determined from the Doppler shift in the wavelengths of their emitted light). This correlation is expressed in the Hubble law: velocity = H × distance, in which H denotes Hubble’s constant, which must be determined from observations of the rate at which the galaxies are receding. There is widespread agreement that H lies between 67 and 73 kilometres per second per megaparsec (km/sec/Mpc). H has been used to determine distances to remote galaxies in which standard candles have not been found. (For additional discussion of the recession of galaxies, the Hubble law, and galactic distance determination, see physical science: Astronomy.)
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The Scope of Astronomy. LH 95 stellar nursery in the Large Magellanic Cloud. The subject of Astronomy is the study of all the kinds of matter and radiation beyond the Earth. Astronomy is an excellent vehicle for studying science because of the sheer diversity of the universe.
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, meteoroids, asteroids, and comets.
21 de dez. de 2022 · The current suite of operational missions includes the Hubble Space Telescope, the Chandra X-ray Observatory, and the James Webb Space Telescope. Additionally, the Fermi Gamma-ray Space Telescope explores the high-energy end of the spectrum.
Discover More Topics From NASA. NASA explores the unknown in air and space, innovates for the benefit of humanity, and inspires the world through discovery.
25 de jun. de 2024 · Scope. Topics covered in the journal include: Observational astronomy. Theoretical astrophysics. Computational techniques in astrophysics. Instrumentation and techniques. Planetary science....
