Lecture 14 - The Sun - Our Parent Star

Lecture 14 - The Sun - Our Parent Star - The Sun - Our...

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The Sun - Our Parent Star ASTRONOMY 3 Lesson 14 1 The chromosphere of the Sun observed in H α - see http://antwrp.gsfc.nasa.gov/apod/ ap040611.html The black circle is Venus transiting in front of the Sun.
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NATURE of the Universe Review of Lesson 13 Astronomy - The Sun: Our Parent Star • Among the large moons in the solar system , we can find quite a variety: Io has volcanoes , Europa is covered by ice, and might house an ocean below the ice, and Titan has a dense atmosphere . • The rings around Jovian planets are primarily caused by moons which came too close and were disrupted by tidal forces . The critical distance is called the Roche limit , which corresponds to 2.5 times the radius of the planet . • Pluto has recently been reclassified as a “dwarf planet ”. It is one of the largest members of the Kuiper belt (a remnant of the formation of the Solar System) . 2
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NATURE of the Universe Questions from Lesson 13 Astronomy - The Sun: Our Parent Star Think about (questions from Lesson 13): • Are sunspots really black? • Does the Sun always shine with the same intensity? 3
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• Measuring the Sun (Ch. 9.1) • Atmosphere of the Sun (Ch. 9.3) • Sunspots (Ch. 9.4) • Flares and solar wind (Ch. 9.4) NATURE of the Universe Today’s Topics Astronomy - The Sun: Our Parent Star 4
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NATURE of the Universe Measuring the Sun Astronomy - The Sun: Our Parent Star Measuring the Sun: Which properties would you measure? • Size • Mass • Rotation period • Temperature • Brightness and Energy Output (Luminosity) • ... 5
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NATURE of the Universe Measuring the Sun Astronomy - The Sun: Our Parent Star The size of the Sun: The Sun angular diameter as seen from Earth: 30 arcmin The distance between the Sun and Earth: 1 Astronomical Unit (150 Million km) => The Sun has a diameter of 10 times the diameter of Jupiter (1.4 Million km) density = mass / volume = 1,400 kg/m 3 The Sun has the same average density as Jupiter ! The temperature of the Sun’s photosphere is 5780 K . The mass of the Sun: The mass of the Sun can be computed from the semimajor axis and orbital periods of the planets and Newton’s laws => The Sun has 1000 times the mass of Jupiter (2 * 10 30 kg). The average density of the Sun: 6
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NATURE of the Universe Measuring the Sun Astronomy - The Sun: Our Parent Star From this we can compute the total power output of the Sun to 4 * 10 26 W . We call this the luminosity of the Sun . The apparent brightness of the Sun (or any star) scales with the distance. The further away we are from the Sun, the fainter it appears. For comparison, in 2005 the average electricity demand in California was 3 * 10 10 W (or 300 million 100-W lightbulbs or 30,000 Megawatt). Above Earth’s atmosphere (i.e. at a distance of
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Lecture 14 - The Sun - Our Parent Star - The Sun - Our...

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