Starlight pp 145-173 | Cite as

First Look Inside a Star – The Atmosphere

  • Keith Robinson
Part of the Patrick Moore's Practical Astronomy Series book series (PATRICKMOORE)


As astronomers, we soon learn that the blindingly brilliant visible face of the Sun is called the photosphere, and we could be forgiven for thinking that this is some kind of precisely defined surface, like the surface of a planet. However, all stars including the Sun are entirely gaseous, and the photosphere consists of what amounts to the inner part of a star’s surface layers – in effect, its atmosphere. It is a layer of gas of finite depth that is relatively dense, and so it is the principal source of the continuum part of a star’s spectrum. However, photons that are emitted within the photosphere and which escape from its topmost layers do so as a result of having traveled along a range of paths of both varying distance and optical depth. This has interesting consequences for the overall appearance of the Sun’s photosphere and maybe that of other stars, too.


Absorption Line Optical Depth Color Index High Energy Level Spectral Class 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.ScotforthUK

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