Page 21 - Curriculum Visions Dynamic Book

fusion The joining of atomic nuclei to form
heavier nuclei.
matter Anything that exists in physical form.
micron A millionth of a meter.
molecule A group of two or more atoms held together by chemical bonds.
nasa The National Aeronautics and Space Administration.
payload The spacecraft that is carried into space by a launcher.
photon A particle (quantum) of electromagnetic radiation.
solar panels Large flat surfaces covered with thousands of small photoelectric devices that convert solar radiation into electricity.
The core
At the center of the Sun is a region called the core. It is where much of the matter of the star is transformed by fusion from hydrogen to helium, and also where energy is released (see pages 8–9).
The radiative zone
The radiative zone is the region outside the core.
It reaches through 55% of the Sun’s radius. In this zone the energy from the core is carried outward by particles of energy called photons.
In the incredibly dense matter within the Sun each photon, once created, moves about 1 micron before being absorbed by a gas molecule. The absorption of the photon heats up the gas molecule, and that makes it reemit another photon. The new photon then travels another micron before it, too,
is absorbed.
The process of producing photons and absorbing them happens all the way through the radiative zone. By the time a photon has reached the outside of the radiative zone, its predecessors have collided with gas molecules between 1019 (ten with 19 zeros after it) and 1025 (ten with 25 zeros after it) times.
Even at the speed of light a journey involving 1019 collisions can take hundreds of thousands to millions of years. So, the light we see from the Sun, which takes 8 minutes to reach us, may actually have been created in the core of the Sun more than tens of millions of years ago!
Each time a photon is absorbed and a new one released, the photon is absorbed and reemitted
at lower and lower temperatures. That alters the wavelength of the energy. The result is that although the energy near the core is mainly gamma ray photons, by the time that energy reaches the surface, it is primarily in wavelengths that produce visible light photons.
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