Glossary term: Radiação eletromagnética
Description: Quando os físicos do século XIX descreveram os fenômenos elétricos e magnéticos, descobriram que há uma maneira de os padrões de campos elétricos e magnéticos se propagarem juntos pelo espaço na velocidade da luz, mesmo em situações em que não há cargas elétricas por perto. Essas ondas são conhecidas como ondas eletromagnéticas ou radiação eletromagnética. As ondas eletromagnéticas elementares podem ser classificadas de acordo com seus comprimentos de onda, e o espectro eletromagnético resultante inclui, dos comprimentos de onda mais curtos aos mais longos: raios gama, raios X, ultravioleta, luz visível, infravermelho, ondas submilimétricas e ondas de rádio (incluindo ondas milimétricas/microondas). A radiação eletromagnética de objetos astronômicos distantes é a fonte mais importante de informações dos astrônomos sobre esses objetos.
Related Terms:
- Força eletromagnética
- Raio gama
- Infravermelho (IV)
- Luz
- Radiação de micro-ondas
- Ultravioleta
- Espectro visível
- Astronomia submilimétrica
- raio X
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
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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In Other Languages
- Árabe: الإشعاع الكهرومغناطيسي
- Alemão: Elektromagnetische Strahlung
- Inglês: Electromagnetic Radiation
- Espanhol: Radiación electromagnética
- Francês: Rayonnement électromagnétique
- Hindi: इलेक्ट्रोमॅग्नेटिक रेडिएशन (विद्युतचुंबकीय विकिरण)
- Italiano: Radiazione elettromagnetica
- Japonês: 放射 (external link)
- Coreano: 전자기복사
- Marathi: इलेक्ट्रोमॅग्नेटिक रेडिएशन (विद्युत चुंबकीय विकिरण)
- Chinês Simplificado: 电磁辐射
- Chinês Tradicional: 電磁輻射
Related Diagrams
Radiação de corpo negro
Caption: As curvas da radiação emitida por corpos negros de diferentes temperaturas. O eixo x mostra o comprimento de onda e o eixo y mostra a quantidade de energia emitida a cada segundo por um metro quadrado da superfície desse corpo negro em cada comprimento de onda.
Quanto mais quente o corpo, menor o comprimento de onda e mais azul a luz em que ele emite sua quantidade máxima de energia. Apesar de o corpo mais frio nesse gráfico ter um pico de luz vermelha, todos os outros corpos mais quentes emitem mais luz vermelha do que o corpo mais frio.
Credit: IAU OAE/Niall Deacon
License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons
Radiação de corpo negro - Catástrofe do UV
Caption: As curvas da radiação emitida por corpos negros de diferentes temperaturas. O eixo x mostra o comprimento de onda e o eixo y mostra a quantidade de energia emitida a cada segundo por um metro quadrado da superfície desse corpo negro em cada comprimento de onda.
Quanto mais quente o corpo, menor o comprimento de onda e mais azul a luz em que ele emite sua quantidade máxima de energia. Apesar de o corpo mais frio nesse gráfico ter um pico de luz vermelha, todos os outros corpos mais quentes emitem mais luz vermelha do que o corpo mais frio.
A linha pontilhada mostra a radiação emitida prevista pela teoria clássica antes da mecânica quântica moderna. Essa previsão tende ao infinito em comprimentos de onda mais curtos para qualquer temperatura de corpo negro acima de zero e foi chamada de "catástrofe do ultravioleta".
Credit: IAU OAE/Niall Deacon
License: CC-BY-4.0 Creative Commons Attribution 4.0 International (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 Attribution 4.0 International (CC BY 4.0) icons
