ast101 lecture 8

define nuclear fusion

the process of combining atoms with smaller nuclei into one larger one.

define nuclear fission

the process of splitting one larger nuclei into multiple smaller ones

how does the sun generate energy?

the sun generates energy through nuclear fusion of hydrogen into helium

roughly how much of the solar system’s mass is contained in the sun?

over 99%

what is the core?

the innermost layer of the sun where fusion takes place

what would happen if the temperature in the core dropped?

the core would shrink, raising the pressure and the temperature

define hydrostatic equilibrium

the balance between the pull of the suns gravity and the push of the gas pressure within the sun

what is the radiative zone?

the second layer of the sun where heat escapes from the core

what is the convective zone?

the third, lower density layer of the sun where gas moves around

what is convection?

the cycle of cool air sinking and hot air rising

what is the photosphere?

the “surface” of the sun

why does the sun look opaque?

the mean free path of light becomes longer at the photosphere, so light can travel easily to our eyes

what is mean free path?

how long something can travel before running in to something and changing direction

what is solar wind?

the outflow of particles from the sun

what are sunspots?

cooler regions on the “surface” of the sun that appear darker than the areas around them, usually seen in pairs

what is the chromosphere?

the lowest density area of the sun right above the surface that conducts heat to the outer layer

what is the corona?

a layer of gas right outside the chromosphere that allows solar wind to escape via holes

when can you see the chromosphere and corona?

during a total eclipse

which layer of the sun makes up the most of its mass?

the core

list the layers of the sun in order from innermost to outermost

core, radiative zone, convective zone, photosphere + sunspots, chromosphere, corona

how do we know how old the sun is?

we know how long life has been on earth, thus the sun must be at least that old

what is the ball of fire theory and why is it false?

the theory that the sun is perpetually burning, if it were true the sun would only last 80,000 years

what is compression theory and why is it false?

the theory that the sun is gas being squeezed and thus heating up, it must be false because the sun must shrink by over 25m per year