Star

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False-color imagery of the Sun, a G-type main-sequence star, the closest to Earth

A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye from Earth during the night, appearing as a multitude of fixed luminous points in the sky due to their immense distance from Earth. Historically, the most prominent stars were grouped into constellations and asterisms, the brightest of which gained proper names. Astronomers have assembled star catalogues that identify the known stars and provide standardized stellar designations. However, most of the stars in the Universe, including all stars outside our galaxy, the Milky Way, are invisible to the naked eye from Earth. Indeed, most are invisible from Earth even through the most powerful telescopes.

For at least a portion of its life, a star shines due to thermonuclear fusion of hydrogen into helium in its core, releasing energy that traverses the star's interior and then radiates into outer space. Almost all naturally occurring elements heavier than helium are created by stellar nucleosynthesis during the star's lifetime, and for some stars by supernova nucleosynthesis when it explodes. Near the end of its life, a star can also contain degenerate matter. Astronomers can determine the mass, age, metallicity (chemical composition), and many other properties of a star by observing its motion through space, its luminosity, and spectrum respectively. The total mass of a star is the main factor that determines its evolution and eventual fate. Other characteristics of a star, including diameter and temperature, change over its life, while the star's environment affects its rotation and movement. A plot of the temperature of many stars against their luminosities produces a plot known as a Hertzsprung–Russell diagram (H–R diagram). Plotting a particular star on that diagram allows the age and evolutionary state of that star to be determined.

A star's life begins with the gravitational collapse of a gaseous nebula of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. When the stellar core is sufficiently dense, hydrogen becomes steadily converted into helium through nuclear fusion, releasing energy in the process.[1] The remainder of the star's interior carries energy away from the core through a combination of radiative and convective heat transfer processes. The star's internal pressure prevents it from collapsing further under its own gravity. A star with mass greater than 0.4 times the Sun's will expand to become a red giant when the hydrogen fuel in its core is exhausted.[2] In some cases, it will fuse heavier elements at the core or in shells around the core. As the star expands it throws a part of its mass, enriched with those heavier elements, into the interstellar environment, to be recycled later as new stars.[3] Meanwhile, the core becomes a stellar remnant: a white dwarf, a neutron star, or if it is sufficiently massive a black hole.

Binary and multi-star systems consist of two or more stars that are gravitationally bound and generally move around each other in stable orbits. When two such stars have a relatively close orbit, their gravitational interaction can have a significant impact on their evolution.[4] Stars can form part of a much larger gravitationally bound structure, such as a star cluster or a galaxy.

Observation history[edit | edit source]

People have seen patterns in the stars since ancient times.[5] This 1690 depiction of the constellation of Leo, the lion, is by Johannes Hevelius.[6]
The constellation of Leo as it can be seen by the naked eye. Lines have been added.

Historically, stars have been important to civilizations throughout the world. They have been part of religious practices and used for celestial navigation and orientation. Many ancient astronomers believed that stars were permanently affixed to a heavenly sphere and that they were immutable. By convention, astronomers grouped stars into constellations and used them to track the motions of the planets and the inferred position of the Sun.[5] The motion of the Sun against the background stars (and the horizon) was used to create calendars, which could be used to regulate agricultural practices.[7] The Gregorian calendar, currently used nearly everywhere in the world, is a solar calendar based on the angle of the Earth's rotational axis relative to its local star, the Sun.


The oldest accurately dated star chart was the result of ancient Egyptian astronomy in 1534 BC.[8] The earliest known star catalogues were compiled by the ancient Babylonian astronomers of Mesopotamia in the late 2nd millennium BC, during the Kassite Period (ca. 1531–1155 BC).[9]

The first star catalogue in Greek astronomy was created by Aristillus in approximately 300 BC, with the help of Timocharis.[10] The star catalog of Hipparchus (2nd century BC) included 1020 stars, and was used to assemble Ptolemy's star catalogue.[11] Hipparchus is known for the discovery of the first recorded nova (new star).[12] Many of the constellations and star names in use today derive from Greek astronomy.

In spite of the apparent immutability of the heavens, Chinese astronomers were aware that new stars could appear.[13] In 185 AD, they were the first to observe and write about a supernova, now known as the SN 185.[14] The brightest stellar event in recorded history was the SN 1006 supernova, which was observed in 1006 and written about by the Egyptian astronomer Ali ibn Ridwan and several Chinese astronomers.[15] The SN 1054 supernova, which gave birth to the Crab Nebula, was also observed by Chinese and Islamic astronomers.[16][17][18]


External links[edit | edit source]

 
  1. ^ Bahcall, John N. (June 29, 2000). "How the Sun Shines". Nobel Foundation. Retrieved 2006-08-30. 
  2. ^ Richmond, Michael. "Late stages of evolution for low-mass stars". Rochester Institute of Technology. Retrieved 2006-08-04. 
  3. ^ "Stellar Evolution & Death". NASA Observatorium. Archived from the original on 2008-02-10. Retrieved 2006-06-08. 
  4. ^ Iben, Icko Jr. (1991). "Single and binary star evolution". Astrophysical Journal Supplement Series. 76: 55–114. Bibcode:1991ApJS...76...55I. doi:10.1086/191565. 
  5. ^ a b Forbes, George (1909). History of Astronomy. London: Watts & Co. ISBN 1-153-62774-4. 
  6. ^ Hevelius, Johannis (1690). Firmamentum Sobiescianum, sive Uranographia. Gdansk. 
  7. ^ Tøndering, Claus. "Other ancient calendars". WebExhibits. Retrieved 2006-12-10. 
  8. ^ von Spaeth, Ove (2000). "Dating the Oldest Egyptian Star Map". Centaurus International Magazine of the History of Mathematics, Science and Technology. 42 (3): 159–179. Bibcode:2000Cent...42..159V. doi:10.1034/j.1600-0498.2000.420301.x. Retrieved 2007-10-21. 
  9. ^ North, John (1995). The Norton History of Astronomy and Cosmology. New York and London: W.W. Norton & Company. pp. 30–31. ISBN 0-393-03656-1. 
  10. ^ Murdin, P. (November 2000). "Aristillus (c. 200 BC)". Encyclopedia of Astronomy and Astrophysics. Bibcode:2000eaa..bookE3440.. doi:10.1888/0333750888/3440. ISBN 0-333-75088-8. 
  11. ^ Grasshoff, Gerd (1990). The history of Ptolemy's star catalogue. Springer. pp. 1–5. ISBN 0-387-97181-5. 
  12. ^ Pinotsis, Antonios D. "Astronomy in Ancient Rhodes". Section of Astrophysics, Astronomy and Mechanics, Department of Physics, University of Athens. Retrieved 2009-06-02. 
  13. ^ Clark, D. H.; Stephenson, F. R. (June 29, 1981). "The Historical Supernovae". Supernovae: A survey of current research; Proceedings of the Advanced Study Institute. Cambridge, England: Dordrecht, D. Reidel Publishing Co. pp. 355–370. Bibcode:1982ASIC...90..355C. 
  14. ^ Zhao, Fu-Yuan; Strom, R. G.; Jiang, Shi-Yang (2006). "The Guest Star of AD185 Must Have Been a Supernova". Chinese Journal of Astronomy and Astrophysics. 6 (5): 635–640. Bibcode:2006ChJAA...6..635Z. doi:10.1088/1009-9271/6/5/17. 
  15. ^ "Astronomers Peg Brightness of History's Brightest Star". NAOA News. March 5, 2003. Retrieved 2006-06-08. 
  16. ^ Frommert, Hartmut; Kronberg, Christine (August 30, 2006). "Supernova 1054 – Creation of the Crab Nebula". SEDS. University of Arizona. 
  17. ^ Duyvendak, J. J. L. (April 1942). "Further Data Bearing on the Identification of the Crab Nebula with the Supernova of 1054 A.D. Part I. The Ancient Oriental Chronicles". Publications of the Astronomical Society of the Pacific. 54 (318): 91–94. Bibcode:1942PASP...54...91D. doi:10.1086/125409. 
    Mayall, N. U.; Oort, Jan Hendrik (April 1942). "Further Data Bearing on the Identification of the Crab Nebula with the Supernova of 1054 A.D. Part II. The Astronomical Aspects". Publications of the Astronomical Society of the Pacific. 54 (318): 95–104. Bibcode:1942PASP...54...95M. doi:10.1086/125410. 
  18. ^ Brecher, K.; et al. (1983). "Ancient records and the Crab Nebula supernova". The Observatory. 103: 106–113. Bibcode:1983Obs...103..106B.