ASTR 1020 1st Edition Lecture 5What controls the Sun?- Fusion requires temperatures of million degreesGRAVITATIONAL EQUILIBRIUMPressure from FUSION pushing OUTGravity from MASS pulling INForces EQUAL: Pressure outward=Gravity inwardSPHERICAL –nature of gravity makes it roundWeight of upper layers compresses lower layers Fusion in the Sun’s Core- Gravity compresses the H in the core to very high pressure and temperatures- Temperature and density are high enough (15 million K) to allow nuclear fusion to sustain outward pressure.o The rate of nuclear fusion is extremely sensitive to temperature Why isn’t there a runaway reaction, where fusion makes the core hotter, further increasing the rate of nuclear fusion (making the core yet hotter, etc.)?The Solar ThermostatToo cold: less fusion (less pressure), contracts, heats, more fusion, expandsToo hot: more fusion, expansion, cools, less fusion, contracts NEGATIVE FEEDBACK?The temperature bounces in and out How does the energy get out of the core?- Core temp= 15 million Ko Hot and dense from the gravitational pressure of all that mass- Fusion Produces:o Helium –stays in coreo Neutrinos –no interaction=GONE !o Gamma rays –energy! (transporting energy)o Positrons –quickly find electrons to annihilate with more gamma raysRadiative Zone- Gamma ray photons travel via RADATION- Interior of Sun is very dense. Photons cant go very far before they’re absorbed (~1 mm).- Energy is continuously absorbed and re-emitted, “Random Walk” moving generally outward.- Takes ~50,000 years for energy to leave Sun!Convection Zone- Eventually, gas has cooled to (only) a few million Kelvino No longer redirects photons, absorbs them- Heat travels via CONVECTIONo Hotter regions rise, cooler regions sink (energy carried as heat in gas)- Energy continues to work its way out (nearly 1 million yrs to get to surface)Photosphere (the “surface of the Sun”)- Material cools during journey from core, but particularly during convection- T-core=15-5 million K- T-radiative = 5-2 million K- T-convection =2 x 10^6 -10^4 K- T-photosphere = ~6000 KQ: In the core, what kind of light is most common? Gamma RaysQ: At the photosphere, what kind of light is most common? Visible Photosphere- Photons can leave the Suno “cooled” (T = 5800K) to visible energieso Photosphere is the “visible surface” of the SunGranulation - Result of convection- Typical= 1000-2000 km across- Only last 8-15 minutesSunspots- Darker =coolero Still ~4,000 K- Sunspot pictured at the bottom left covers the area of 15 Earths!Sunspots Caused by MAGNETIC FIELDS- Magnetic fields trap gas in huge bubble loops- Cooler areas at “liftoff” cause dark sunspots What Causes the Magnetic Field Lines to Stick Out Like That?- Differential Rotationo The Sun rotates differently at different latitudes.o 24 days at equator, 39 days near poles (the sun winds itself up)This Solar “Wind Up” Leads To the Sunspot Cycle**11-year solar cycle (maybe because how magnetic field lines wind up)**Sunspots Form At different Latitudes during the cycle- Spots form at higher latitudes during maxima and lower latitudes during minimaIf we see the sunspot edge-on, we can see the loops standing off the surface: PROMINENCEReview of Recitation Lab of the beginning of the weekHEIGHT OF THE C4C (Learning Goal #1:- There can be many right ways to do itLine up triangle with roof (used shadows, measured angles, or counted bricks)Goal #2:- “What is the right answer?” is complicated - HISTOGRAM –how many measurements fall in each range?o 6 groups measure 17-18 meters o 3 groups measures 28-29 meterso Combined data of 2 classes: Most data in “bell curve” at 10-20 meters- How can we get a better estimate?o Take all the results and measure them?Gaussian (Normal) Distribution- Aka, the “bell curve” –common distribution in natureCHECK SLIDE FOR PICTURE OF STANDARD DEVIATION- Number of measurements x height of C4C (meters)- Mean=15.3 meters- Standard deviation of our data =4.3m- Height =15.3+- 4.3 meters !Take away points:- Science relies on different people making different measurements with different techniques- An individual measurement doesn’t mean much- Look at a mean or median to determine the answer and a standard deviation to know how accurate it may be- More measurements=better overall knowledge- Always make sure you result makes