The Sun

How do we determine the interior structure of the Sun?

we use physics and observations to infer the interior structure, since we only see the outer layers of the Sun

What does the inside of the Sun look like?

at each point within the Sun, the outward push of pressure is balanced by the inward pull of gravity - the energy radiated from the surface of the Sun balances the energy produced in its interior (the Sun is very balanced)

What is hydrostatic equilibrium?

outward radiative pressure = inward force of gravity

Why is hydrostatic equilibrium important?

without it, Sun would be shrinking/expanding rapidly

What are the ideal conditions for nuclear fusion?

density, temperature, and pressure increase toward the center

What is nuclear fusion?

involves the fusing of atomic nuclei - the strong nuclear force binds protons and neutrons together, fusion requires ramming protons together at high speed

What do nuclei consist of?

protons and neutrons

What’s the end result of nuclear fusion?

creates more massive nuclei from less massive ones

How does the Sun generate so much energy?

hydrogen burning

What is hydrogen burning?

fusion of hydrogen into helium in the Sun’s central core - powers all main sequence stars

What does hydrogen fusion create?

positrons and neutrinos

What are neutrinos?

light atomic particles with no electric charge - has very weak interactions with matter, escapes the core freely

What is the inner part of the Sun called?

radiative zone

What is radiative transfer?

photons move out from crowded (hot) regions to cooler ones - energy produced in the Sun’s core must get out

What can affect radiative transfer?

opacity of a material

What is the convective zone?

outer part of the Sun

What is convection?

rising/falling of hot/cool gas, like water boiling

What happens in the photosphere?

temperature decreases outward, increases inward - atmosphere density drops very rapidly with increasing altitude

What is the photosphere?

layer where light is emitted (apparent surface)

What is limb darkening?

the Sun looks dimmer near its edge because we look through less material at the edges

What does the photosphere produce?

complex absorption spectrum - cooler outer layers of the photosphere absorb some of the light from hotter, deeper layers

What is the chromosphere?

above the photosphere, has a higher temperature than the photosphere - gives off a reddish emission-line spectrum

What is the corona?

above the chromosphere, extremely hot, very disperse, emits x-rays, can extend for several solar radii, isn’t visible with the eye unless there’s a solar eclipse

What are sunspots?

cooler areas in the photosphere

What is the structure of sunspots?

dark inner umbra w/ surrounding penumbra

How are sunspots caused?

magnetic fields

What is the solar maxima?

most amount of sunspots and activity

What are solar prominences?

hot rising gas in the chromosphere constrained by magnetic fields

What are solar flares/coronal mass ejections?

highly energetic, violent bursts and eruptions

What is the heliosphere?

Sun’s reach of influence on its environment

What does the heliosphere do?

solar wind pushes away material and helps protect Earth from harmful cosmic rays