The sun

THE SUN 1 million km wide ball of H, He undergoing nuclear fusion. Contains 99% of the mass in the whole solar system! Would hold 1.3 million earths! 386 billion billion megawatts of power produced. 15 minutes of this is equivalent to all the energy consumed by humans in 1 year. 4 million tons of H are consumed every second, but there is enough to burn for another 5 billion years!

THE SUN 150M km (93M miles; 8 light-minutes; 1 AU) from Earth 1 Rs = 700,000 km = 100 Re 1 Ms = 2 x 1030 kg = 300,000 Me Mean density = 1.4 g/cm3 Energy flux at Earth (solar constant) = 1400 W/m2  4 x 1026 W luminosity Rotation: differential, 25 days at equator, 35 days at poles Figure: near-perfect sphere; < 10 km of oblateness Surface gravitational acceleration: 274 m/s2 Surface temperature about 5800 K Core temperature about 13.6 million K Core pressure about 150 billion atmospheres Core density 150 x water (150,000 kg/m3)

P-p chain fusion

How does this provide energy? 1 He weighs slightly less than 4 H…

For how long will the Sun burn? Sun will stay in current evolutionary track until 10% of H is consumed. H burning is 0.7% efficient e.g. mass to energy conversion due to mass difference between H and He Sun burns at rate of 3.846 x 1026 J/s What does this mean in terms of actual energy? Every second, the sun converts 500 million metric tons of hydrogen to helium. Due to the processes of fusion, 5 million metric tons of excess material is converted into energy in each second. This means that every year, 157,680,000,000,000 metric tons are converted into energy. The material from one second of energy is about 1x1027 (one octillion thousand) watts of energy. On Earth, we receive about 2/1,000,000,000 (two billionths) of that energy, or about 2x1018 (two quintillion) watts. This is enough energy to power 100 average light bulbs for about 5 million years -- longer than humans have been standing upright.

How does this compare to other sources? Combustion: 1 kg of coal per square meter per second… …will last 10,000 years Gravitational contraction (Kelvin-Helmholtz): Falling objects convert gravitational energy to heat Matter “falls” into the Sun due to contraction Contraction by 20 m per year…. What does this mean in terms of actual energy? Every second, the sun converts 500 million metric tons of hydrogen to helium. Due to the processes of fusion, 5 million metric tons of excess material is converted into energy in each second. This means that every year, 157,680,000,000,000 metric tons are converted into energy. The material from one second of energy is about 1x1027 (one octillion thousand) watts of energy. On Earth, we receive about 2/1,000,000,000 (two billionths) of that energy, or about 2x1018 (two quintillion) watts. This is enough energy to power 100 average light bulbs for about 5 million years -- longer than humans have been standing upright. …will last 100 million years

Hydrostatic Equilibrium

Wien’s Displacement Law

Solar interior Core: totally ionized; fusion reactions occur; 15M K Radiation zone: ionized, dense and variably transparent (opaque over short distances) to radiation; random walk of photons and continual absorption and re-radiation  takes 104 to106 years to traverse; 7M K Convective zone: energy more efficiently transported via convection cells; 2M K

Spherical Harmonic Normal Modes

Helioseismology

Rotational speeds within the Sun. Red = fastest Blue = slowest Inner 70% rotates at uniform rate This image shows differences in the speed of rotation of material inside the Sun. The false colours represent speed; red material is rotating the fastest, dark blue the slowest. The inner 70% or so of the Sun rotates at nearly the same rate. However there is marked differential rotation in the outer 30%, which corresponds to the solar convection zone where the energy is carried upwards by convection rather than by radiation. Note that the equator rotates much faster than the poles. Outer 30% has differential rotation due to convection zone

Solar interior Photosphere: bubbling surface of the sun where most of visible light comes from; has 1000 km scale granularity (top of convection cells) that exist for 15-20 minute timescales; 5800 K Chromosphere: thin (2000 km) cool (4500 K) skin over photosphere; pink color due to H Transition zone: rapid rise in temperature Corona: vast, extremely hot and ionized cloud around sun; 1M K

chromosphere

UV He ion emission Upper part of chromosphere at 60000 K Prominence 60-80000 K Corona 1M K

Corona Highly ionized zone (1M-3M K) Why so hot??!!

Extends to 706,000 km +

Corona in the extreme UV Coronal loops Coronal holes

extreme UV Fe ion (14+) emission Dark = coronal hole (magnetic field opens out to space and source of high-velocity solar wind)

soft X-ray Bright = hot spots in corona Dark at top = coronal hole

Radio Acquired near solar maximum

Sunspots Slightly cooler areas on the photosphere (4500 K) 10,000 km wide Several day to month lifetimes Locations of twisted and compressed magnetic field lines Migration can be used to track differential rotation of Sun 11 year cycle; number of sunspots related to amount of solar activity

We are currently at an unusually quiet and long-lived minimum…

magnetogram

UV image

Magnetic field polarity flips during 11-year sunspot cycle Complete cycle from N to S to N takes 22 years

Solar Wind Supersonic flow of material from photosphere and corona. Has sufficient kinetic energy to achieve escape velocity 400 km/sec + Extends outward for 10M km

Prominences: 100,000 km scale ejections of mass Usually closed loops around magnetic field lines Relatively cool clouds of H gas

X-rays Bright area is active region in corona (coronal condensation) associated with a flare and sunspot group

Solar Flares Short-lived, sudden increases in brightness (and associated jets of material and release of large amount of energy) near sunspots Bursts of electromagnetic energy as magnetic field lines “snap”

Coronal Mass Ejection

Very damaging space weather phenomenon associated with magnetic storms in the Earth’s ionosphere Can disable spacecraft and ground electrical and telecommunication systems