AST 115 1st Edition Lecture 21 Outline of Last Lecture I. The Source of the Sun’s Energya. PossibilitiesII. The Proton – Proton Chain a. Deuteronb. Positronc. NeutrinoIII. The Solar Neutrino “Mystery”a. Raymond Davisb. What’s wrong?Outline of Current LectureI. Interior of the Sun (Theory)II. Interior of the Sun (Observations)a. Two ways of making observations of the interior of the SunIII. Introduction to Ch. 10: Characterizing StarsIV. Measuring the Distances to StarsCurrent Lecture Interior of the Sun (Theory)o We can use the knowledge of physics to estimate (by calculation) the conditions inside the Sun.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- The material in the Sun should behave like a gas on Earth does. (a pressure-temperature relation: ideal gas law. If pressure increases, so does the temperature and vise versa)- The Sun is neither expanding nor contracting. (Hydrostatic equilibrium: a pressure-depth law. Pressure increases with depth)- The Sun is not cooling of (Thermo Equilibrium: rate at which energy leaves the surface equals the rate at which it reaches the surface from the interior. Energy transferred by radiation, or by convection)- There must be an internal energy source for the Sun. (Thermonuclear fusion of hydrogen into helium). (Solution to the equation: “model of the Sun”) Temperature at the center ~ 15.6 million ˚K Density at the center ~ 150 g/cm3 The models of the Sun show estimated temperature, pressure, density, and chemical composition from the center to the surface. Interior of the Sun (Observations)o Two ways to make observations of the Sun:- Helioseismology – sound waves traveling through the interior show up as surface pulsations.- Direct probes (via neutrinos emitted from core, produced during hydrogen fusion) Although elusive, these solar neutrinos have been detected. Super-Kamiokande Solar Neutrino Detector in Japan (contains 50,000 tons of pure water and uses 13,000 light detectors)Introduction to Chapter 10: Characterizing Stars Measuring the distances to starso The basic method uses trigonometry and is called “surveying”. It is based on the phenomenon of “parallax”.o Stellar parallax = apparent shift in position of a nearby star as we change our vantage point while the Earth orbits the Sun.-Distance=1Stellar Parallax Angle-d=1p (d = distance ; p = stellar parallax angle)- The angle must be in arc seconds (“)- Distance is in parsecs- Where 1 pc = 3.26 LY- Example: Alpha Centauri has p = 0.742” d=10.742 = 1.35 pcd=4.39 light years (converted to LY)o Maximum Distance using Stellar Parallaxd(max)=1p(min)- From Earth, p(min) ~ 0.01 arc secSo d(max) ~ 100 pc ~ 326 LY- New methods, eg. HIPPARCOSo p(min) ~ 0.001 arc seco So d(max) ~ 1000 pc = 1kpcor ~ 3260 LY*This is much smaller than the size of our Galaxy. Other methods have been discovered to increase our distance – measuring
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