Editing Sun (section)

=== Radiative zone ===
{{Main|Radiative zone}}
[[File:Heat Transfer in Stars.svg|thumb|300x300px|Illustration of different stars' internal structure based on mass. The Sun in the middle has an inner radiating zone and an outer convective zone.|alt=See caption]]
The radiative zone is the thickest layer of the Sun, at 0.45 solar radii. From the core out to about 0.7 [[Solar radius|solar radii]], [[thermal radiation]] is the primary means of energy transfer.<ref name="autogenerated1">{{cite web |url=http://mynasa.nasa.gov/worldbook/sun_worldbook.html |publisher=NASA |title=Sun |website=World Book at NASA |access-date=10 October 2012 |url-status=dead |archive-url=https://web.archive.org/web/20130510142009/http://mynasa.nasa.gov/worldbook/sun_worldbook.html |archive-date=10 May 2013}}</ref> The temperature drops from approximately 7&nbsp;million to 2&nbsp;million kelvins with increasing distance from the core.<ref name="NASA1" /> This [[temperature gradient]] is less than the value of the [[adiabatic lapse rate]] and hence cannot drive convection, which explains why the transfer of energy through this zone is by [[radiation]] instead of thermal convection.<ref name="NASA1" /> [[Ions]] of hydrogen and helium emit photons, which travel only a brief distance before being reabsorbed by other ions.<ref name="autogenerated1" /> The density drops a hundredfold (from 20,000&nbsp;kg/m<sup>3</sup> to 200&nbsp;kg/m<sup>3</sup>) between 0.25 solar radii and 0.7 radii, the top of the radiative zone.<ref name="autogenerated1" /><!-- http://adsabs.harvard.edu/abs/2008SoPh..251..101M -->