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Glossary term: 星云

Description: 星云是一种遥远的天体,具有云的外观。通常,星云由星际气体和尘埃组成。在历史上,星云一词指的是所有延展的、边缘模糊的天体,包括我们今天所认识的星系--像银河系这样的遥远恒星系统。如今,星云一词仅限于指代星际介质中的气体和尘埃云,即星系内恒星之间的气体和尘埃。星云被分为许多不同的种类:分子云相对较冷,颜色较暗,主要由分子氢组成;新的恒星就是在这样的云中形成的。巨型分子云可以包含多达数百万个太阳质量的氢气。年轻恒星频繁地喷射出狭窄的电离气体喷流;当这些喷流激发周围的气体时,就会形成一种叫做赫比-哈罗(Herbig–Haro)天体的星云。当大质量恒星形成后,它们的强烈辐射会使周围的气体发出特征性的红光;这种由炽热的电离氢气组成的星云被称为 HII 区(电离氢区)。其他类型的星云与恒星的死亡有关:低质量恒星的死亡会留下不断膨胀的气体外壳,这种星云(命名上有些令人困惑)被称为行星状星云。当大质量恒星以超新星的形式爆发时,喷出的气体会形成一种叫做超新星遗迹的星云。

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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".

Related Diagrams


Sagittarius is shaped like a teapot pouring tea south west. The ecliptic runs WSW to ENE at the top of the constellation

Sagittarius Constellation Map

Caption: The constellation Sagittarius along with its bright stars and surrounding constellations. Sagittarius is surrounded by (going clockwise from the top) Aquila, Scutum, Serpens Cauda, Ophiuchus, Scorpius, Corona Australis, Telescopium, Microscopium and Capricornus. The brighter stars in Sagittarius form a distinctive teapot shape. Sagittarius lies on the ecliptic (shown here as a blue line), this is the path the Sun appears to take across the sky over the course of a year. The Sun is in Sagittarius from mid December to mid January. The other planets of the Solar System can often be found in Sagittarius. Sagittarius lies south of the celestial equator. The famous teapot asterism is visible for all but the most arctic regions of the world but the most southerly parts of the constellation are not visible in northern parts of Asia, Europe and North America. Sagittarius is most visible in the evenings in the northern hemisphere summer and southern hemisphere winter. The supermassive black hole Sagittarius A* which lies at the center of our Milky Way Galaxy is sits on the western (here right-hand) edge of Sagittarius. Due to it covering an area at the center of our Galaxy, Sagittarius is home to many star clusters including open clusters (marked here with yellow circles) and globular clusters (marked here with yellow circles with + signs superimposed on them). Three nebulae are also marked here with green squares. The y-axis of this diagram is in degrees of declination and with north as up and the x-axis is in hours of right ascension with east to the left. The sizes of the stars marked here relate to the star's apparent magnitude, a measure of its apparent brightness. The larger dots represent brighter stars. The Greek letters mark the brightest stars in the constellation. These are ranked by brightness with the brightest star being labeled alpha, the second brightest beta, etc., although this ordering is not always followed exactly. The dotted boundary lines mark the IAU's boundaries of the constellations and the solid green lines mark one of the common forms used to represent the figures of the constellations. Neither the constellation boundaries, nor the lines joining the stars appear on the sky.
Credit: Adapted by the IAU Office of Astronomy for Education from the original by IAU/Sky & Telescope

License: CC-BY-4.0 Creative Commons 署名 4.0 国际 (CC BY 4.0) icons

Related Activities


Reading the Rainbow

Reading the Rainbow

astroEDU educational activity (links to astroEDU website)
Description: By understanding how rainbows work, you can discover about light and its properties, learning about stars, nebulae, galaxies, and our Universe.

License: CC-BY-4.0 Creative Commons 署名 4.0 国际 (CC BY 4.0) icons

Age Ranges: 14-16 , 16-19 , 19+
Education Level: Informal , Middle School , Secondary , University
Areas of Learning: Interactive Lecture , Observation based , Social Research
Costs: Low Cost
Duration: 1 hour 30 mins
Group Size: Group
Skills: Analysing and interpreting data , Asking questions , Engaging in argument from evidence