About the Sun

 The sun is made of several regions the core: the radiative zone, the convective zone, the photosphere, the chromosphere and the corona.

                At the center of the sun is the core. Extending from the center of the sun to a radius of approximately 43,500 km (~27,000 miles), the core is more than 150 times denser than water and reaches temperatures of roughly 16,000,000 K (28,800,000 °F). Every second, the core converts 600 million metric tonnes (1,322,772 million pounds) of hydrogen to 596 million metric tonnes (1,313,953 million pounds) of helium. The remaining 4 million metric tonnes of hydrogen is converted into energy roughly equivalent 3.84 x1026 W. For scale, most power plants in the United States produce power in the Mega Watt scale, or 106 W. The core is the only part of the sun where it is hot and dense enough to produces a significant amount of heat to allow thermonuclear reactions to occur. Other regions of the sun are heated by energy transfer from the core.

                After the core comes the radiative, or radiation, zone which extends from the core to about 130500 km (81,088 miles), and ranges in temperature from 10,000,000 K to 2,000,000 K (18,000,000°F -3,600,000°F) . Energy from the core is transferred through a diffusion process- a process in which particles mix together due to their natural movement caused by thermal, pressure, or concentration gradients [2, 3].  Due to the high density of both the core and the radiative zone, the particles undergo multiple collisions with each other making them travel in a random path. It is estimated that it takes as much as a few thousand years for the energy from the core to reach the outer surface of the radiative zone [1].

                 The convection zone extends from the end of the radiative zone to the visible surface of the sun. The density at the surface of this zone is about double of air at seas level on Earth and temperature in this zone ranges from 2,000,000 K to 5,778 K (3,600,000°F -9,941°F) at the surface. This difference in temperature is large enough to allow for the plasma in the sun to be transported by bulk convection. Hot plasma will rise to the surface, cool, and then sink back to the bottom of the convective zone.

                After the convective zone comes the photosphere, which is the visible surface of the sun. The photosphere is only about 100-500 km (62 mi – 311 mi) thick, and has a particle density of about 1% of air at sea level on earth.  This zone has a temperature of 5778 K (9,941°F) and emits most of the radiation from the sun. Several solar features can be observed on the photosphere, which are described under the Solar Phenomena tab. The diameter of the sun is generally given as the diameter of the photosphere.

                 Located 2,000 to 5,000 km (1,242.742 mi -3,106.856 min) above the photosphere is the chromosphere. Hydro-magnetic waves and compression waves caused by features in the photosphere heat the chromosphere to temperatures between 10,000 K and 50,000 K (17,540 °F- 89,540°F).

                The outermost region of the sun is called the corona. The corona is essentially the atmosphere of the sun, has no well-defined outer surface, and unlike Earth, is filled with plasma.  The corona is the only part of the sun that can be seen during the moment of totality in a total solar eclipse. The corona emits x-rays and its temperature ranges from about 500,000 K to 2,000,000 K (899,540°F -3,599,540°F).



[1] Pisacane, V. L. (2016). The space environment and its effects on space systems. Reston, VA: American Institute of Aeronautics and Astronautics.

[2] Turns, S. R. (2012). An introduction to combustion: concepts and applications. New York: McGraw-Hill, Connect Learn Succeed.

[3] Diffusion. (n.d.). Retrieved July 24, 2017, from https://www.merriam-webster.com/dictionary/diffusion