The Sun

Layers of the Sun _____ - ~15 million K, 25% radius __________ zone ~60% radius ________________ – to the surface __________ (visible surface) ~5800K Limb darkening Sun spots ____________ - ~10,000K – very thin _______ - may be several million K Core Radiative Convective Zone Photosphere Chromosphere Corona

The Sun’s Atmosphere Photosphere – temp. ______ (average) Layer we see – the surface Chromosphere – a thin layer, a few 1000 km thick, at a temperature between _______________. Can be seen during _____________. Corona – ______________, 1,000,000 km thick, at a temperature of about ___________. 5800 K 4,000 – 10,000 K solar eclipses Outermost layer 1,000,000 K

Outer layers of sun 1 = photosphere, 2 = chromosphere, 3 = corona

Photosphere

Granulation Convection Zone

Limb Darkening

Limb darkening

the “surface” of the sun “Free streaming” photons travel to us without running into much matter “Photosphere” the “surface” of the sun -- where the photons we see emerge from the sun and start to “free stream” “Random Walk” in the interior of the sun, photons are constantly absorbed and scattered by matter

Sunspots are low temperature regions in the photosphere ________ are about 4000 K (2000 K cooler than solar surface) and have ______________ up 1000 the normal solar magnetic field. They can be as large as 50,000 km and last for ___________. Sunspots magnetic fields many months

Sunspots are low temperature regions in the photosphere The large _____________ in sunspots decrease the flow of heat via convection causing the _____________________. magnetic fields sunspot to become cool

Sunspots Umbra Penumbra Granulation

Sunspot cycle

Sunspots can be used to measure the rotation of the Sun Near the ______ the Sun rotates once in ________. The _____ rotate more slowly, about once every ___ ____. equator 25 days poles 36 days

Chromosphere

Corona

Corona “heats up” over a very small distance

Solar Magnetic Field Existence of a ___________ & its complex structure is because of the ________________ and __________ in the atmosphere hot corona solar magnetic field vibrations cartoon of magnetic field lines on sun X-ray pictures of Sun

Magnetic field loops – SOHO satellite

Solar magnetic fields also create other phenomena __________ ______ ________ _______ _____ _________ Prominences Flares Solar wind Coronal mass ejections

Prominences - Cooler than photosphere.

Solar flares - Hotter, up to 40,000,000 K More energetic

Solar Flare 4K solar flare footage captured by NASA

Coronal mass ejections - eruption of gas, can reach Earth and affect aurora, satellites

Coronal mass ejection

“Northern Lights” (Aurora Borealis) Particles in the solar wind slam into Earth’s atmosphere, ________________ Nitrogen & Oxygen which then __________, emitting the photons we see as _______. collisions excite de-excite aurora

Sun at Different Wavelengths Temperature ___________ determines which lines we see Use to our advantage: if we look only at ____________ (wavelengths), we only see gas at certain temperatures – allows us to probe different parts of the sun (photosphere, chromosphere, corona, …) certain lines

Sun at Different Wavelengths 6563 Angstroms -- H (Balmer) line of Hydrogen (tells us about _____________) chromosphere

Sun at Different Wavelengths 195 Angstroms (UV) – _______________ ____________ transition region and corona

Sun at Different Wavelengths X-rays (______) corona

The Sun’s Interior Structure Photosphere Energy transport via convection Flow of energy Energy transport via radiation Energy generation via nuclear fusion Temp, density and pressure decreases outward

The Sun’s Interior Core The region where _______ ______ takes place. Temp. ~ 15 million degrees K. Radiation Zone ______ is transported ______ primarily by ________. Temp. ~ 10 million degrees K. ________________. Convection Zone ______ is transported through _________. nuclear fusion Energy outward photons No nuclear fusion Energy convection

The Moon’s orbit around the Earth would easily fit within the Sun!

The Equilibrium Between Gravity and Pressure The ____________ and ________ at the center of the Sun increases due to _____________________. Without a force to counter gravitation force, the Sun will continue to contract. However, once the condition for _____________ is reached, the energy released by the fusion process is enough to maintain a high enough temperature and pressure to __________________________. That is, the gravitational force pulling materials inward is balanced by the outward force of thermal pressure. This balance is maintained until the nuclear fuel is exhausted. temperature density gravitational contraction nuclear fusion resist the gravitational collapse

The Energy Source of the Sun Today, we understand that the energy source of the Sun is the ___________________ which combines hydrogen nuclei to form helium. The increase of temperature at the center of the Sun due to gravitational contraction eventually triggers nuclear fusion, which converts some of the mass into energy, according to _____________________ ________________. nuclear fusion process Einstein’s mass-energy equation, E = mc2 Electric charge is not conserved! This is a simplified picture that’s not exactly correct.

Proton-Proton Chain

Why Does Nuclear Fusion Occurs Only at the Center of the Sun? Temperature is a measurement of the average _____________ of the particles. Gas at very ________________ move at very __________. High speed is needed to overcome the __________ __________________ between the protons to get them very close to each other. Once the protons are close to each other, the _____________ ______ can bind them together. kinetic energy high temperatures high speeds repulsive electromagnetic force strong nuclear force

Fusion of Hydrogen into Helium E = mc2

E = m c 2 A little mass equals a LOT of energy. Example: (c = speed of light) But where does the Energy come from? c2 is a very large number! A little mass equals a LOT of energy. Example: 1 gram of matter  1014 Joules (J) of energy. Enough to power a 100 Watt light bulb for ~32,000 years!

How does the energy generated at the center get to the surface and to us? The ______ generated by the nuclear fusion process is _______ in the form of ______ (radiative energy). The photons interact with the solar plasma (mostly the electrons). Each time a photon encounters an electron, it _________________. Thus, the photons go through a ______ path to the surface. energy released photons changes its direction zig-zag It takes about 1 million years for a photon to travel from the center of the Sun to its surface. The ‘random walk’ of photon to the surface.

https://www.youtube.com/watch?v=1jYabtziQZo http://orvedahl.bitbucket.org/Software/Animations/random_walk.avi

Energy Transport within the Sun Temperature falls farther from core - more and more non-ionized atoms capture the photons Gas becomes opaque to light in the convection zone

Hot gas is less dense and rises Convection Convection takes over when the gas is too opaque for radiative energy transport. Hot gas is less dense and rises Cool gas is more dense and sinks

How do we Observe the Internal Structure of the Sun? Almost all the ________ from the Sun originates from the _________ of the Sun. To ‘see’ inside the Sun, we need to use special observational methods: ______________. ________________________. radiation outer layers Helioseismology Solar Neutrino Observations 1. Helioseismology The study of how the _______ of the Sun moves – expands and contracts, can tell us about the internal structure of the Sun. We observe the ______ of the solar surface by observing the _____________ of light. surface motion Doppler shift

Helioseismology Helioseismology The study of how the surface of the Sun moves – expands and contracts, can tell us about the internal structure of the Sun. This is similar to how we study the internal structure of the Earth by studying how sound waves propagate through Earth. The surface of the Sun is oscillating up and down due to the excitation of seismic waves. We observe the motion of the solar surface by observing the Doppler shift of light from the surface of the Sun. The red and blue patches represent regions of solar surface receding inward (red) and bulging outward (blue). The surface of the Sun is oscillating up and down due to the excitation of seismic waves. Different seismic wave travels through different part of the solar interior. Thus, by studying the behavior of the seismic waves, we can infer the internal structure of the Sun. Paths of wave

Neutrino Observatories Homestake Neutrino Detector in South Dakota, 1.5 km underground. Neutrino detectors are placed underground to shield them from other unwanted interaction with other cosmic ray particles. Kamiokande Neutrino Detector, Japan Sudbury Neutrino Observatory in Canada, 2 km underground. The 12 meter diameter tank contains 1,000 tons of heavy water.

Looking Under The Solar Surface – Neutrino Observation Solar Neutrino Experiment – 2002 Nobel Price in Physics Knowing how many neutrinos the proton-proton chain produces, we can predict how many neutrinos we can expect to see from the Sun.

The Solar Neutrino Problem A type of elementary particle (_____ different flavors, actually) with very low mass and interacts only through the weak (nuclear) force  Not easily detectable— From the many trillions of neutrinos passing through the neutrino detectors every second, only roughly one neutrino a day is expected to be recorded! three

The Solar Neutrino Problem Should observe one solar neutrino per day in neutrino detectors. Only get ____ solar neutrino every _____ days.  Theory of the _______________________?  We don’t really understand neutrinos? There are ______ different types of neutrinos. Existing detectors only see ____ of the 3 types. Neutrinos ___________ into a different type of neutrino after they were generated, thus reducing the number of neutrinos detectable. New neutrino detectors sensitive to all three. Early results indicated that the number of solar neutrinos is consistent with our model of the Sun! one three structure of the Sun is wrong three one may change

http://phobos. physics. uiowa http://phobos.physics.uiowa.edu/~kaaret/sgu_s05/260,1,Outer Layers of the Sun http://astron.berkeley.edu/~eliot/Astro7A/290,1,Slide 1 http://www.lancs.ac.uk/depts/physics/teaching/py263/PPT/348,3,Slide 3 http://www.ifa.hawaii.edu/users/lin/ast110-6/259,3,The Structure of the Sun – The Internal Structure http://www.physics.sfasu.edu/markworth/ast105/257,2,Sunspots