turbo-1 said:This page will explain it better than I could, but the fact is that as a star enters this phase, it becomes very large, and the radiation becomes less-energetic (shifted toward the red end of the spectrum), thus "red giant".
http://www.historyoftheuniverse.com/starold.html
Yes, the proton-fusing shell gives a new energy source to the star, and this radiative pressure reverses the collapse of the star and causes the outer regions of the star to be pushed out (thus the giant). The radiation loses energy traversing this extra thickness of star-stuff, resulting in longer wavelength emissions (thus the red). When our sun does this, the Earth will have had to suffer a long period of declining radiation (icy planet syndrome), only to be toasted like a marshmallow when the proton-fusing shell lights off and causes the sun to swell.orange said:Thanks mate.
If I understood it correctly, the radiation generated from the proton-fusing shell surrounding the alpha-particle core, has less energy when it reaches the photosphere than when protons are fused in the core.
The term "red giant" refers to a stage in the life cycle of a star. As a star ages and runs out of hydrogen fuel, its core begins to collapse and its outer layers expand, causing it to grow larger and cooler. This expansion and cooling causes the star to emit more red light, which is why it appears red to our eyes. Hence, the name "red giant".
No, not all giant stars are red. The color of a giant star depends on its temperature, which in turn depends on its mass. Stars with lower mass and temperature may appear more orange or yellow, while stars with higher mass and temperature may appear more blue or white.
The size of a red giant star varies depending on its initial mass. On average, red giants can range from 100 to 1,000 times the size of our sun. However, some red giants can grow even larger, reaching sizes of up to 1,000,000 times the size of our sun.
The duration of the red giant phase also varies depending on the initial mass of the star. On average, a star will spend about 10% of its total lifetime as a red giant. For a star like our sun, this can last for about 1 billion years.
After a star has completed its red giant phase, it will continue to evolve and eventually shed its outer layers to form a planetary nebula. The remaining core of the star will then become a white dwarf, which will gradually cool and dim over time.