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16.1 Physical properties of the sunstar= a glowing ball of gas held together by its own gravity and powered bynuclear fusion at its center-Relatively normal star lying right in the middle of the observed ranges of stellarmass, radius, brightness, and compositionOverall propertiesThe Sun’s mass is 2.0×10^30 kgSolar rotation= can be measured by timing sunspots and other surface featuresas they traverse the solar disk-Sun rotates in a month-The sun spinsdifferentially, like Jupiter and Saturn faster at the equator andslower at the poles-Solar rotation can be measured by timing sunspots and other surface features asthey traverse the solar diskSunspots are never seen above latitude 60° (north or south), but at that latitude,they indicate a 31-day period-The distribution of solar radiation has the approximate shape of a blackbodycurve for an object at about 5800 K. The average solar temperature obtained inthis way is known as the Sun’seffective temperature.Solar structurephotosphere=The “surface” part of the Sun that emits the radiation we see lyingabove the uppermost layer of the sun’s interior and below chromo-sphere-solar corona= The outer portion of the sun, normally too faint to be seen, butvisible during an eclipsechromosphere= Sun’s lower atmosphere, Just above the photospheretransition zone= region in which the temperature rises dramatically separatesthe sun’s chromosphere from the coronasolarcorona= outer atmosphere of the sun. lies above the chromosphere and atgreat distances turns into solar windsolar wind= an outward flow of fast-moving charged particles from the sun.spreads across the entire solar systemconvection zone= a region where the material of the Sun is in constantconvective motionradiation zone= region of the suns interior where extremely high temperaturesguarantee that the gas is completely ionized. Photons only occasionally interactwith electrons and travel through this region with relative ease. The area in whichsolar energy is transported toward the surface by radiation rather than byconvection-The termsolar interioris often used to mean both the radiation and convectionzones.centralcore= the site of powerful nuclear reactions that generate the Sun’senormous energy output
LuminosityThe Sunradiatesa great deal of energy into space, uniformly (we assume) in alldirections. By holding a light-sensitive device a photoelectric cell, perhapsperpendicular to the Sun’s rays, we can measure how much solar energy isreceived per square meter of the surface area every second.solar constant= The amount of solar energy reaching this surface each second-value is approximately 1400 watts per square meter-About 50 to 70 percent of the incoming energy from the Sun reaches Earth’ssurface; the rest is intercepted by the atmosphere (30 percent) or reflected awayby clouds (0 to 20 percent)Luminosity= one of the basic properties used to characterize stars, defined asthe total energy radiated by stars each second, at all wavelengths-

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