Glossary term: Estrela
Description: Uma estrela é uma bola de plasma - núcleos atômicos separados de seus elétrons - que é mantida unida por sua própria gravidade e impedida de entrar em colapso pela pressão interna que é consequência dos processos de fusão nuclear nas regiões centrais da estrela. Os astrônomos, em um leve abuso da nomenclatura física, costumam usar "gás" e "plasma" de forma equivalente e, portanto, também se referem às estrelas como bolas de gás. Na atmosfera de uma estrela, o plasma pode estar apenas parcialmente ionizado e (dependendo da temperatura da estrela) até mesmo conter alguns átomos.
A estrela mais próxima da Terra é o Sol.
Em um sentido mais geral, a palavra "estrela" inclui protoestrelas, onde a fusão nuclear ainda não começou, e remanescentes estelares, como estrelas de nêutrons ou anãs brancas, que são duas possibilidades (dependendo da massa) de transformação das estrelas depois de esgotado o combustível para a fusão nuclear. Esses remanescentes estelares não são simplesmente bolas de plasma - uma anã branca pode se cristalizar em um tipo incomum de sólido depois de se resfriar por bilhões de anos, e as estrelas de nêutrons têm uma grande semelhança com núcleos atômicos gigantescos.
Sejam elas observadas a olho nu ou por meio de telescópios de luz visível, as estrelas são os objetos mais evidentes no céu noturno. No cosmos, elas são normalmente encontradas dentro de galáxias, cada estrela geralmente acompanhada por um ou mais planetas. O estudo de como as estrelas se formam e evoluem é um importante subcampo da astrofísica.
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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher The translation of this term and its definition is still awaiting approval
The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".
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A gravitational lens magnifies one of the first stars
Caption: This image zooms in on a star formed within the first billion years after the birth of the Universe (at a redshift of 6.2). The Hubble Space Telescope detected this light using a technique called gravitational lensing. A massive galaxy cluster between the observer and the imaged star creates a distorted and warped image of the parent galaxy and reveals its features.
Credit: NASA, ESA, B. Welch (JHU), D. Coe (STScI), A. Pagan (STScI)
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Watchtower and Paddy Fields Under the Starry Sky
Caption: Winner in the 2022 IAU OAE Astrophotography Contest, category Still images of celestial patterns.
This image, taken in April 2022, shows the sky over a plantation field around a century-old watchtower guarding a village in the province of Guangdong, China. Throughout the ages, the sky has been used as a tool for navigation and also as a calendar. By watching the apparent movement of the stars, it is possible to follow the passing of time, thereby understanding the change of the seasons which in turn helps to plan out the best timings of agricultural work.
The most prominent constellations in this image are Orion and Canis Major, the Great Dog. Commonly associated with a giant hunter in Greek mythology, Orion is followed by his hound in the shape of the constellation Canis Major.
In China, the seven bright stars of the constellation Orion are paradoxically called Three Stars (Shen) and this is one of the 28 Lunar Mansions. The Babylonian pre-zodiac, the so-called “Path of the Moon”, had 17 constellations and included Orion (therein named “True Shepherd of the Heavens”). This is not really surprising because, even in the system of the 88 modern constellations, the Moon sometimes stands in the constellation Orion. The modern constellation boundaries were defined in the 1920s in such a way that the area of Orion ends a half degree south of the ecliptic, in order to avoid the Sun entering it. Still, the Moon and the planets do occasionally. Therefore, Orion is part of the Zodiac (a stripe 5 to 10 degrees around the ecliptic), part of the path of the Moon and, of course, also used by many cultural calendars all over the world.
Sirius, the bright star in the left half of the photograph, is the brightest star in the night sky, and has been used by many indigenous cultures to determine their calendars; the Egyptians awaited the Nile flood with Sirius’s heliacal rise, while the Romans connected its reappearance after its invisibility in daylight with the hottest summer time. In Old China, Sirius was considered a single-star asterism called The Wolf. The adjacent area was called The Market for Soldiers and the area in the southern part of Canis Major was imagined as the Bow with an Arrow.
The reddish bright star in the top right corner is Betelgeuse, a red supergiant and one of the largest stars that can be seen with the naked eye. Orion’s Great Nebula below Orion’s Belt should be mentioned, but also the fainter huge red arc that is called Barnard’s Loop is clearly shown in this photograph. This galactic nebula and the circular red nebula around Orion’s not-so-bright head are both parts of star-forming regions, while the red nebula to the upper left of Orion is the Rosette Nebula in the unrecognisable constellation of Monoceros.
Credit: Likai Lin/IAU OAE
License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
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