Loading...

Glossary term: Tipo espectral

Description: As estrelas são classificadas em tipos espectrais de acordo com a presença de características em seus espectros.

Para a maioria das estrelas, o tipo espectral baseia-se principalmente na temperatura da superfície estelar e segue uma sequência: O, B, A, F, G, K e M, listados da mais quente à mais fria. Essa sequência foi recentemente ampliada para incluir os tipos mais frios L, T e Y. Esses três representam, em sua maioria, anãs marrons, mas alguns objetos com tipo espectral L são estrelas, e não anãs marrons.

Existem também letras para classificar classes especiais de estrelas. Estrelas de carbono são aquelas com características espectrais marcantes decorrentes de moléculas que contêm carbono. Elas são classificadas como tipo C. Estrelas do tipo S são intermediárias entre os tipos K ou M e C, pois as abundâncias de oxigênio e carbono na superfície são quase iguais. As anãs brancas são divididas em uma série de tipos diferentes com base nas características de seus espectros; todos esses tipos começam com a letra D (DA, DB, etc.). Estrelas quentes e massivas com linhas de emissão largas têm uma série de tipos que começam com W (WN, WC, WO).

A notação atual é um legado da primeira tentativa moderna de classificação, realizada no Observatório do Harvard College. As classes, originalmente designadas de A a Q em ordem alfabética, foram posteriormente reordenadas como uma sequência de temperatura, resultando nos principais tipos ainda utilizados hoje. As principais classes espectrais são subdivididas, denotadas pelos números de zero a nove. O Sol é do tipo espectral G2. Letras adicionais referem-se a características especiais (como “e” para estrelas com linhas de emissão brilhantes), e a classe de luminosidade, indicada por algarismos romanos, também pode ser especificada.

Related Terms:



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".

If you notice a factual or translation error in this glossary term or definition then please get in touch.

In Other Languages

Related Diagrams


Seven lines. The peak of each line moves from short wavelengths for the top line to longer wavelengths for the bottom line.

Stellar spectral types

Caption: The spectra of seven stars ordered by spectral type ranging from the hottest (O-type) at the top to the coolest (M-type at the bottom). The x-axis shows the wavelength of light and the y-axis is a measure of the flux of light received at that wavelength. Each spectrum is normalized (the flux at each wavelength is divided by the maximum flux in that spectrum) and the spectra are then offset from each other along the y-axis to make the plot easier to view. The colour of the lines between 400 nm and 700 nm roughly corresponds to the colour the human eye would see light of that wavelength. Below 400 nm and above 700 nm, where the human eye can see little to no light, the lines are coloured blue and red respectively. The hotter stars have more of their flux at the bluer end of the spectrum and the cooler stars have more of their flux at the redder end. However the total amount of flux a star emits depends on its size and temperature. Due to this, a hot star will emit more red light than a cool star of the same size even if the cool star emits almost all its light in red light but this is not visible in this plot due to the normalization mentioned above. The sharp, narrow drops in the spectra are absorption lines caused by atoms and ions in the stars’ atmospheres. The strength of a spectral line depends on the temperature of a star’s atmosphere. Take the hydrogen line at 656.5 nm as an example. All of the stars in this plot are primarily made of hydrogen, but the 656.5 nm hydrogen line is weak for the hottest and coolest stars but strongest for spectral types A and F. This is because hydrogen absorbs more light at 656.5 nm at the temperatures of A and F stars’ atmospheres than in hotter or cooler stars. The coolest star here, the M-type star, has wide absorption bands in its spectra. This is because this star is cool enough to have compounds such as titanium oxide in its atmosphere. These compounds, often called molecules in astronomy, produce wider spectral absorption features than atoms or ions.
Credit: IAU OAE/SDSS/Niall Deacon

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons


Seven bands with bright and dark patches. The brightest part of the band moves from blue in the top band to red at the bottom

Stellar spectral types - bands

Caption: The spectra of seven stars ordered by spectral type ranging from the hottest (O-type) at the top to the coolest (M-type at the bottom). The x-axis shows the wavelength of light while the brightness or darkness at each wavelength corresponds to the flux of light received from the star at that wavelength with darker patches having less flux and brighter patches more. Each spectrum is normalized (the flux at each wavelength is divided by the maximum flux for that spectrum) so that the maximum flux should appear with the same brightness for all the spectra. The colour plotted between 400 nm and 700 nm roughly corresponds to the color the human eye would see light of that wavelength. Below 400 nm and above 700 nm, where the human eye can see little to no light, the lines are coloured blue and red respectively. The hotter stars have more of their flux at the bluer end of the spectrum and the cooler stars have more of their flux at the redder end. However the total amount of flux a star emits depends on its size and temperature. Due to this, a hot star will emit more red light than a cool star of the same size even if the cool star emits almost all its light in red light but this is not visible in this plot due to the normalization mentioned above. The dark, narrow patches in the spectra are absorption lines caused by atoms and ions in the stars’ atmospheres. The strength of a spectral line depends on the temperature of a star’s atmosphere. Take the hydrogen line at 656.5 nm as an example. All of the stars in this plot are primarily made of hydrogen, but the 656.5 nm hydrogen line is weak for the hottest and coolest stars but strongest for spectral types A and F. This is because hydrogen absorbs more light at 656.5 nm at the temperatures of A and F stars’ atmospheres than in hotter or cooler stars. The coolest star here, the M-type star, has wide absorption bands in its spectra. This is because this star is cool enough to have compounds such as titanium oxide in its atmosphere. These compounds, often called molecules in astronomy, produce wider spectral absorption features than atoms or ions.
Credit: IAU OAE/SDSS/Niall Deacon

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

The Office of Astronomy for Education is hosted by the Haus der Astronomie on the campus of the Max Planck Institute for Astronomy in Heidelberg. The Office of Astronomy for Education is an office of the International Astronomical Union, with substantial funding from the Klaus Tschira Foundation and the Carl Zeiss Foundation. The Shaw-IAU Workshops on Astronomy for Education
are funded by the Shaw Prize Foundation.