Our Sun

Why do we care about the Sun...

- Light, heat, life

- Space weather solar wind (1,000,000 mph) flares (UV, x-ray radiation)

disturb Earth's magnetic field → power surges

excess radiation bad for satellites

Why do we care about the Sun...

- Light, heat, life

- Space weather solar wind (1,000,000 mph) flares (UV, x-ray radiation)

disturb Earth's magnetic field → power surges

excess radiation bad for satellites

- ...one day it's gonna get us

Layers of the Sun

Core- very very hot (15 million K)

- thermonuclear fusion (H → He)

- 4 million tons of matter per second converted to energy

Radiative Zone- heat transfer through radiation (surprise!)

- photons are absorbed and re-emitted: “random walk”

- few 100,000 years

Convective Zone- heat transfer through convection (another surprise!)

- granulation

- core → surface: ~ 1 million years

Bright areas: hot pockets of gas move up

Dark lanes: cool pockets of gas sink down

Convection -- Granulation

Smaller granules join together,expand, and then split up.

Granules

Atmosphere- photosphere: what you see! (sunspots, granulation)

- the “surface”

Atmosphere - chromosphere: lower atmosphere

- we can see it during eclipses

Atmosphere- corona: upper atmosphere

- very hot, tenuous gas

- we can see it during eclipses

Atmosphere- corona: upper atmosphere

- very hot, tenuous gas

- we can see it during eclipses

The corona is really hot, and no one knows why.(It’s 250x hotter than the surface of the sun!)

. . .Magnetic field ?

Sunspots

Strong magnetic fields block convection cells

→ cooler areas (darker)

Sunspots

Sunspots

- on the photosphere

- formed by differential rotation ~equator: 25-day period ~poles: 35-day period

Sunspots

- on the photosphere

- formed by differential rotation ~equator: 25-day period ~poles: 35-day period

- they're picky about location

- high latitude → low latitude

- “butterfly diagram”

Sunspots

11-year Solar Cycle

Prominences

loops of gas

Flares

eruptions of gas near sunspots

Coronal Mass Ejection (CME)

ejected bubbles of gas

Charged particles interact with Earth’s magnetic field.

Northern Lights

Northern Lights

Particles in Earth’s atmosphere get excited.