page_title: Convection
section_title: Stellar physics
hierarchical_section_title: Convection / Examples and applications / Stellar physics
caption_attribution_description: Artist's impression of the structure of a solar-like star and a red giant. The two images are not to scale - the scale is given in the lower right corner. It is common to divide the Sun's (and solar-like stars') interior into three distinct zones: The uppermost is the Convective Zone. It extends downwards from the bottom of the photosphere to a depth of about 15% of the radius of the Sun. Here the energy is mainly transported upwards by (convection) streams of gas. The Radiative Zone is below the convection zone and extends downwards to the core. Here energy is transported outwards by radiation and not by convection. From the top of this zone to the bottom, the density increases 100 times. The core occupies the central region and its diameter is about 15% of that of the entire star. Here the energy is produced by fusion processes through which hydrogen nuclei are fused together to produce helium nuclei. In the Sun, the temperature is around 14 million degrees. In red giants, the convection zone is much larger, encompassing more than 35 times more mass than in the Sun.
context_page_description: Convection is the transfer of heat due to the bulk movement of molecules within fluids, including molten rock. Convection includes sub-mechanisms of advection, and diffusion.
  Convection cannot take place in most solids because neither bulk current flows nor significant diffusion of matter can take place. Diffusion of heat takes place in rigid solids, but that is called heat conduction. Convection, additionally may take place in soft solids or mixtures where solid particles can move past each other.
  Thermal convection can be demonstrated by placing a heat source at the side of a glass filled with a liquid, and observing the changes in temperature in the glass caused by the warmer fluid circulating into cooler areas.
  Convective heat transfer is one of the major types of heat transfer, and convection is also a major mode of mass transfer in fluids. Convective heat and mass transfer takes place both by diffusion – the random Brownian motion of individual particles in the fluid – and by advection, in which matter or heat is transported by the larger-scale motion of currents in the fluid.
context_section_description: The convection zone of a star is the range of radii in which energy is transported primarily by convection.
  Granules on the photosphere of the Sun are the visible tops of convection cells in the photosphere, caused by convection of plasma in the photosphere. The rising part of the granules is located in the center where the plasma is hotter. The outer edge of the granules is darker due to the cooler descending plasma. A typical granule has a diameter on the order of 1,000 kilometers and each lasts 8 to 20 minutes before dissipating. Below the photosphere is a layer of much larger "supergranules" up to 30,000 kilometers in diameter, with lifespans of up to 24 hours.
caption: An illustration of the structure of the Sun and a red giant star, showing their convective zones. These are the granular zones in the outer layers of these stars.
exif: {"Image ImageDescription": "Artist's impression of the structure of a solar-like star and a red giant. The two images are not to scale - the scale is given in the lower right corner. It is common to divide the Sun's (and solar-like stars') interior into three distinct zones: The uppermost is the Convective Zone. It extends downwards from the bottom of the photosphere to a depth of about 15% of the radius of the Sun. Here the energy is mainly transported upwards by (convection) streams of gas. The Radiative Zone is below the convection zone and extends downwards to the core. Here energy is transported outwards by radiation and not by convection. From the top of this zone to the bottom, the density increases 100 times. The core occupies the central region and its diameter is about 15% of that of the entire star. Here the energy is produced by fusion processes through which hydrogen nuclei are fused together to produce helium nuclei. In the Sun, the temperature is around 14 million degrees. In red giants, the convection zone is much larger, encompassing more than 35 times more mass than in the Sun."}