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Transcript
The Sun and Other Stars Sunny Facts • The sun is 330,000 times the mass of the earth; diameter is 109x the earth. • 99.86% of the mass of the solar system (Jupiter is 0.1%) • our sun is of “average” size; 5780 K at surface, 12 million degrees K at the core • primarily composed of hydrogen 73.5% and helium; 2% heavy elements • is around 4.6 billion years old, slightly less than half of its lifespan. Sunspots • The sun actually rotates faster at the equator than at the poles (Jupiter also does this). • The sun has “weather,” which consist of darker patches on the surface called sunspots, which can be 10,000 km across. They can last for months. • Sunspots are colder than the rest of the sun: 4300-5000 K. • Sunspots appear in cycles that last around 11 years. What Color is the Sun? • The sun is appears to be yellow because of scattering of light in the earth’s atmosphere. It is actually white. It is called a “yellow” star because most of its radiation is in the yellow-green portion of the electromagnetic spectrum. • The sun has an atmosphere of plasma, called the corona, which extends millions of km into space. Solar Emission Spectrum Why does the Sun emit light? • The massive gravity of the sun squeezes atoms together, overcoming repulsive forces between the atoms’ nuclei • When (hydrogen) atoms fuse, they become a heavier element, helium, and a bit of matter is converted into energy • E=mc2 A small bit of matter is converted into a lot of energy! Nuclear Fusion The Electromagnetic Spectrum The Sun’s neighborhood • The sun is 25,000 l-y from the center of the Milky Way. • Imagining our immediate neighborhood as a sphere with the sun at the center extending 17 light years, contains 50 star systems (many with multiple stars). • The Sun is the 4th largest in the neighborhood; most consist of smaller “brown dwarf” stars. TESS Telescope The Inferred Structure of the Sun The Core • Up to about 25% of the earth’s radius, the core’s density can reach 150 g/cc, with a temperature of 13,600,000 K. • The incredible density is caused by the massive size of the sun • The core is rotating faster than the outer areas of the sun, just like the earth • Energy is produced in the core by fusion of hydrogen into helium; 0.7% of mass is converted into energy when hydrogen becomes helium; fusion occurs only in the core, not outer areas. • Our sun contains 8.9 x 1056 hydrogen atoms, and fuses 3.7 x 1038 every second! • This results in 4 million metric tons of matter being converted into energy every second! • Larger stars have higher densities, higher fusion rates, shorter lives; smaller stars the opposite – they will be around for tens of billions of years. The Radiative Zone • From 0.25 to 0.7 solar radius • Energy flows outward from the core as radiation, decreasing in intensity as you rise through the sun • Radiation is transferred from one atom to another via absorption and emission by electrons around atoms • The sun’s magnetic field is believed to originate in the radiative zone The Convective Zone • Above the radiation zone, matter is not hot enough for radiative transfer, rather the energy circulates by movement of matter (convection) • Density of top of convective zone is only 0.2 g/ cubic meter. Sunspot Lab • Objective: to graph a set of data and use it to predict future sunspot activity. The Maunder Minimum 1645-1700 Tambora Eruption (1816)