Glossary term: 電磁輻射
Description: 當19世紀的物理學家在描述電磁現象時發現，即使在附近沒有電荷的情況下，電場和磁場也能以光速在空間傳播。這些波被稱為電磁波或電磁輻射。基本電磁波可根據其波長進行分類，由此產生的電磁波譜從較短波長到較長波長包括：伽馬射線、X射線、紫外線、可見光、紅外線、亞毫米波和射電波（包括毫米波/微波）。來自遙遠天體的電磁輻射是天文學家了解這些天體的最重要的信息來源。
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See this term in other languages
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
This is an automated transliteration of the simplified Chinese translation of this term
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In Other Languages
- 阿拉伯語: الإشعاع الكهرومغناطيسي
- 德語: Elektromagnetische Strahlung
- 英語: Electromagnetic Radiation
- 西班牙語: Radiación electromagnética
- 法語: Rayonnement électromagnétique
- 印地語: इलेक्ट्रोमॅग्नेटिक रेडिएशन (विद्युतचुंबकीय विकिरण)
- 義大利語: Radiazione elettromagnetica
- 日語: 放射 (external link)
- 韓語: 전자기복사
- 馬拉提語: इलेक्ट्रोमॅग्नेटिक रेडिएशन (विद्युत चुंबकीय विकिरण)
- 巴西葡萄牙語: Radiação eletromagnética
- 簡體中文: 电磁辐射
Related Diagrams
黑體輻射
Caption: 不同溫度黑體的輻射麯綫。x 軸錶示波長，y 軸錶示黑體錶麵每平方米在每個波長下每秒發射的能量。
溫度越高的物體，波長越短，發齣的最大能量光也越藍。盡管圖中最冷的天體發齣的紅光達到峰值，但其他較熱的天體發齣的紅光都比最冷的天體多。
Credit: IAU OAE/Niall Deacon
License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons
黑體輻射--紫外綫災難
Caption: 不同溫度黑體的輻射麯綫。x 軸錶示波長，y 軸錶示黑體錶麵每平方米在每個波長下每秒發射的能量。
溫度越高的物體，波長越短，發齣的最大能量光也越藍。盡管圖中最冷的天體發齣的紅光達到峰值，但其他較熱的天體發齣的紅光都比最冷的天體多。
虛綫顯示的是現代量子力學之前的經典理論所預測的輻射量。對於任何溫度高於零的黑體，這一預測在較短波長處都趨於無窮大，被稱為 "紫外綫災難"。
Credit: IAU OAE/Niall Deacon
License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons
Stellar Structure
Caption: Stars are balls of plasma. For most of a star’s life it burns hydrogen into helium in its core. This phase of a star’s life is known as the main sequence. Burning hydrogen into helium produces heat, that heat travels out of the star’s core eventually reaching the star’s photosphere (often referred to as the “surface” of the star). From here the heat can radiate into space as various forms of electromagnetic radiation. However, how heat travels from the core to the photosphere depends on the star’s mass.
Imagine a parcel of gas rising inside a star. As it rises, it moves into an area of lower pressure, so it cools down and expands. If the parcel is still hotter, and therefore less dense than its surroundings, it keeps moving upward due to buoyancy. Eventually, it will rise far enough to cool and sink back down. This rising and sinking cycle is called convection. Whether convection occurs depends on how quickly temperature changes as you move away from the star’s core. If the temperature in a star drops rapidly, rising parcels of gas are more likely to stay hotter than their surroundings, so convection dominates as the mode of energy transfer in this part of the star. Conversely if the temperature drops more slowly (i.e. if the temperature gradient is small) then heat will mostly be transferred by radiation (photons).
In the most massive main sequence stars (more massive than about 1.5 times the mass of the Sun, seen here on the left), hydrogen is burned into helium using the CNO cycle. This is highly temperature dependent and thus energy production is concentrated near the center of the star. This leads to a larger temperature gradient and thus a convective core. Further out the temperature gradient becomes smaller and heat transport is dominated by radiation. This is called the radiative zone.
For lower mass stars like the Sun (between 0.3 and 1.5 solar masses, seen here in the middle) hydrogen is burned to helium using a different process (the pp chain). This depends less on the internal temperature than the CNO cycle and so energy production is more distributed in the star’s core. This leads to a smaller temperature gradient and thus a radiative core where convection occurs surrounded by a radiative zone. Going further out the gas becomes cool enough for some elements to hang to on some of their electrons, i.e. not being completely ionised. This partially ionised gas is more opaque to photons, trapping heat. This leads to a large temperature gradient and thus convection.
The lowest mass stars (below 0.3 solar masses, seen here on the right) have no radiative zone and are fully convective.
The arrows in the radiative zone are shown as wavy lines heading out of the star. However, a photon’s journey out of a star is much more complex with each individual photon travelling only a short distance before being deflected by some of the charged particles that make up the plasma of the star’s interior. This leads to a long and winding road that takes millennia instead of the few seconds it would take if the photon did not interact with particles in the plasma.
Credit: Based on a vector diagram by Wikimedia user Д.Ильин which itself is based on a diagram from sun.org
License: CC-BY-4.0 Creative Commons 姓名標示 4.0 國際 (CC BY 4.0) icons
