Helios in Greek and Sol in Roman• Drove his chariot across the sky to

provide daylight

• Returned each night in a huge golden

cup on the river Oceanus

• His son Phaeton drove the chariot one

day but lost control burning Africa and

turning the Ethiopians black

Ra and his barge

Japanese sun goddess Amatersasu

emerges from her cave

The Sun

• Radius is 100 times Earth‟s

• Rotates in ~25 days at Equator and ~40 days at poles

• Mass is 1,000 times Jupiter‟s mass.

• 1 Jupiter = 300 Earths

• Density = 1.4gm/cm3

• Surface Temperature 5780K

Lifetime of the Sun• Sun radiates 1026 watts

• Burning oxygen and hydrogen – sun lasts 18 000 years

• Gravitational potential energy – 30 million years

• But geologists and radioactive dates say billions of years

Hydrogen Fusion

Powers the Sun• Largest bomb USA made

was 15 Megaton Bikini Atoll blast 1954

• Nuclear (Strong force) is a million times the chemical (Electromagnetic force)

• 4 Hydrogen nuclei equal 1 Helium + energy

Binding Energy

• Fission produces energy by

breaking up high mass nuclei

• Fusion produces energy by

forming higher mass nuclei

Fusion Animation

• Protons repel each other since both have positive charge

• Coulomb barrier overcome by temperature of Millions Kelvin

Fusion Animation &

Antiparticles Two protons make a deuterium

ejecting a positron and a neutrino

Neutrino escapes sun in seconds

Positron is antielectron and annihilates an electron => gamma ray

Every particle has an antiparticle

When we make them we always get both – anti-stars, anti-Earths, anti??

A proton and a deuterium make a Helium 3 and a gamma ray

Two Helium 3‟s make a Helium nucleus and release two protons

Mass Disappears(?) • 4 protons have more mass than 1 Helium

• 0.7% of input mass M becomes energy (m=0.007M)

• E=mc2 with E in Joules, m in kg and c=3X108 m/sec

• Per second sun converts 600million tons of Hydrogen to Helium

• 4 million tons of mass to energy

Antiparticles - Positrons• When a particle meets its antiparticle they annihilate

• Producing only energy = gamma rays

• Lucky for us the universe seems to be all matter

Ray Davis‟ Solar Neutrino Detector• Standard Model - four forces, four particles, three families, no gravity

• Average neutrino not stopped by a light year of lead

• First Neutrino detectors only found a third of the expected number

• Problem with sun?, neutrino detector?, neutrinos?

• Won Noble Prize in 2002 for NOT finding something

Sudbury Solar Neutrino Observatory• Neutrinos “oscillate” from electron to muon to tau type

Components of Sun

Core, Radiation Zone,

Convection Zone• Heat/energy produced in hot dense

core (15 million Kelvin)

• Transported by radiation initially and

• By convection after 70% of Radius

• By radiation from Photosphere to Earth

Core, Radiation, Convection Zones,

Photosphere, Chromosphere, Corona

• Each gamma ray photon

produced in core is

absorbed and reemitted

• As possibly two or more

lower energy photons

• Trip to surface takes

~million years

• One gamma ray becomes

~1800 visible photons

Photosphere - Sun with Giant Spots• Effective temperature 5780K so sun is gaseous/plasma throughout

• Photosphere is apparent surface where hot gas becomes opaque H-

• Photosphere is 3400 times less dense than air on Earth – 500km deep

Granulation Movie

• Granules are the top of

convection cells

• About 1000km across

Granulation Model

• Granules last about 20

minutes

• Difference in

temperature between

center and edge is

about 100K

3-D Sun, Near Edge

• Notice granules blocking each other‟s image

• Gas rises/falls with a speed of ~1km/sec

Supergranules & Limb Darkening

• 35,000 km across last about a day &contain ~300 granules

• Best seen in chromospheric network (bright circular areas)

• Edge of sun (limb) appears fainter than the center

Chromosphere in

H-Alpha

• Thin layer above Photosphere ~1000km thick

• Filaments are dark & plage are bright regions

• Spectrum taken during eclipse shows emission lines - curves (chromo) and rings (corona)

Chromosphere and Venus Transit• Temperature increases through chromosphere

• In transition region between Chromosphere and Corona

temperature increases most quickly 10,000-1,000,000K

Spicules on Limb• Spikes of gas rise

7000km through

chromosphere

• They last ~5 minutes

• Seen here in H-Alpha

Corona in X-rays• Corona heated to millions of degrees by flares?, spicules?, ??

• Photosphere emits few X-rays so it is dark

• Some other stars are bright in X-rays so they probably have a corona

Pearly White Corona• Seen during a solar eclipse or with coronagraph

• Light scattered from dust and electrons - continuum

• Emission lines from highly ionized elements

• Very rarified and hot (Millions Kelvin)

Dark Coronal Holes Emit Solar Wind

• Solar Wind speed ~400km/sec and density ~7 protons/cm3

• Sun looses 10 million tons/year or 10-14 solar masses

Helioseismology • Solar surface moves up and down like ocean waves

• 5 minute oscillations were first of millions of modes to be discovered

Oscillation Modes• Sound waves refracted back to surface

• Longer wavelengths reach further into sun

• Wavelength X Frequency = sound speed

• Sound speed gives temperature & density with depth

Differential Rotation

• Red fastest – Blue slowest

• Left side shows rotation

period is ~25 days at equator

and ~40 days at poles

• Right side shows rotation in

interior

The Active Sun

• Surface gas is electrically

charged and moving

• So it generates magnetic

fields

• Notice bright plage regions,

filaments and prominence

Spot Motion and Evolution

• Spots last a

few days to a

month

• Big spots last

longer

• Group of

spots is

called an

active region

Sunspot

Close-up

• Dark central region called umbra Temp~4000K

• Grey surrounding region is penumbra Temp~5000K

Sunspot at Various Heights in Sun

• From photosphere to a few hundred kilometers to chromosphere at few thousand km.

Under A Sunspot• Spots are cooler due to deceased circulation

• Blocked energy is radiated from nearby regions

Latitude of Spot Appearance

• Spots first appear at +/-35 degrees latitude

• Appear closer to equator later in cycle

• Spots from new cycle can overlap with old cycle

Sunspot Number by Year• More sunspots at maximum & sometimes none at minimum

• Number of spots varies with 11 year cycle

• Discovered by Schwabe in 1843

Solar Constant• Solar irradiance more easily measured from above atmosphere

• A change of ~3% would start an ice age

Is the Solar Constant Constant?

• Lack of sunspots: 1645-1715 called

Maunder Minimum

• Coincides with Little Ice Age

Solar „Constant‟ / Sunspot Number• Some stars exhibit brightness changes like rotation & spot cycles

• Ca H&K emission lines from active regions on other stars

Detecting a Sunspot‟s Magnetic Field• Sunspots have magnetic field 1000 times Sun‟s average

field, which is 1000 times Earth‟s magnetic field

• Magnetic fields are seen on some stars

Magnetic Polarity of Spots

Babcock Model• Differential Rotation winds up field lines

• Which loop through the photosphere making a pair of spots

• Spots appear closer to equator during cycle

• Overall field reverses with 22 year cycle

Solar Flare Movie• Flares can last from a few seconds

to hours

• Seen in Visible, UV and X-Rays

• Also seen on other stars in

Visible, UV and X-rays

3rd Largest

Solar Flare in

X-rays

• 28 Oct 2003

• Observed with EIT on

SOHO

• Jupiter sized group in

white light

• Visible to naked eye

3rd Most Powerful Flare

• 28 Oct 2003

• Frames ~30 min

spacing

• Related Coronal

Mass Ejection

• Noise caused by

ejected protons

• X-rays seen from

corona of other

stars

Eruptive

Prominence Over

Half Hour• Magnetically confined gas

which is 70,000K

Flare and Eruptive Prominence

Coronal Mass Ejections

Heliosphere• Solar wind is

eventually stopped

by interstellar

medium

Solar Flares

Affect

Magnetosphere

• Solar flares and coronal mass ejections

• Impact Earth and guided by magnetic field

• Hit upper atmosphere and cause aurora

Sun-Earth-Aurora Connection• Aurora forms oval surrounding magnetic pole

• Big storm → big oval

Aurora Movie by Andre Clay in Alaska