HowStarsFormforclass

HowStarsFormforclass - How do Stars Work? (The Sun - Our...

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How do Stars Work? (The Sun -- Our Star) ASTR2340, Spring 2010 R. Chandar
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Star Basics • Stars are like people in that they are born, grow up, mature, and die. • Like people, stars also affect their surroundings or local environment. • The most massive stars have the most profound affect on their environment. (A star’s mass determines what life path it will take). In fact, the birth and death of “massive” stars is one of the processes which has most shaped the way that the universe has changed over time. • The life of any star can be described as a battle between two forces: – Gravity vs. Pressure • Gravity always wants to collapse the star. Pressure holds up the star.
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The Sun: An Average Star 99.85 % of the total mass of the Solar System is tied up in the sun. Although the sun is a very average star, our existence is tied to the warmth and light it provides. We are going to learn the basic principles which govern the energy output of the sun and allow it to “shine”. In fact, these principles are similar for all stars! Our sun is made of (by mass): 70% Hydrogen, 28% Helium, and 2% everything else (C, N, O, etc). The surface temperature of the sun is about 5800 K, whereas the center is ~ 10 million K
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Solar Structure -- Photosphere • The sun is so hot, it has neither solid nor liquid matter anywhere ( plasma) (as move down into the sun, encounter continually hotter, denser gases). • The sun appears to have a bright, luminous surface (photosphere). This is not a physical surface, but occurs because visible light comes from a specific gas layer. • The photosphere has a nearly Blackbody spectrum, corresponding to an average temperature of 5800 K.
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Photosphere • Effective “surface” of sun – not solid – region we see by eye • Thin atmospheric layer – Few hundred km • Low density gas – 0.01% Earth’s atmosphere • Close-up shows granulation – convection cells • Sunspots – Cooler than surrounding gas • appear dark
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Galileo’s Sunspot Drawings
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Solar Rotation Fastest at Equator Slower at Poles Rotation of sun causes magnetic fields.
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Most Detailed Sunspot Image Ever! Swedish Vacuum Telescope
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Atmospheric Features • Prominences – Loops of hot gas – Base near sunspots – Trace magnetic fields
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Solar Structure -- the Corona The outermost part of the sun’s atmosphere is called the corona, and extends several million km from the top of the chromosphere. In 1940, it was discovered that a spectrum of the corona contains emission lines of a number of highly ionized elements, for example, from FeXIV. The corona also produces X-rays. These require very high
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This note was uploaded on 02/21/2011 for the course ASTR 2340 taught by Professor Rupalichandar during the Spring '10 term at Toledo.

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HowStarsFormforclass - How do Stars Work? (The Sun - Our...

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