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Where did the solar system come from? Astr 221 2015 NW Chs. 8&9 Also: Sun – Moon -Eclipses
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Evidence from Other Gas Clouds We can see stars forming in other interstellar gas clouds, lending support to the nebular theory.
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Was our solar system destined to be? Formation of planets in the solar nebula seems inevitable. But details of individual planets could have been different.
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An oasis of life The only surface liquid water in the solar system A surprisingly large moon Earth and Moon with sizes shown to scale Earth
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Giant Impact
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First QuarterSecond Quarter
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Formation of Lunar Maria Large impact crater weakens crust. Heat build- up allows lava to well up to surface. Early surface is covered with craters. Cooled lava is smoother and darker than surroundings.
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Radius: 6.9 10 8 m (109 times Earth) Mass: 2 10 30 kg (300,000 Earths) Luminosity: 3.8 10 26 watts
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Gravitational equilibrium: Energy supplied by fusion maintains the pressure that balances the inward crush of gravity.
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What is the Sun’s structure? Insert TCP 6e Figure 14.3
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The proton–proton chain is how hydrogen fuses into helium in Sun.
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Sunspots Are cooler than other parts of the Sun ’ s surface (4000 K) Are regions with strong magnetic fields
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Loops of bright gas often connect sunspot pairs.
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The number of sunspots rises and falls in an 11-year cycle. Insert TCP 6e Figure 14.21a unannotated Insert TCP 6e Figure 14.21b unannotated
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The sunspot cycle has something to do with winding and twisting of the Sun ’ s magnetic field.
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Magnetic activity also causes solar prominences that erupt high above the Sun ’ s surface.
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Charged particles streaming from the Sun can disrupt electrical power grids and can disable communications satellites.
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Aurora Borealis
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What causes eclipses? The Earth and Moon cast shadows. When either passes through the other’s shadow, we have an eclipse.
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Lunar Eclipse
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When can eclipses occur? Lunar eclipses can occur only at full moon. Lunar eclipses can be penumbral, partial, or total.
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Solar Eclipse
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When can eclipses occur? Solar eclipses can occur only at new moon. Solar eclipses can be partial, total, or annular.
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Why don’t we have an eclipse at every new and full moon? –The Moon’s orbit is tilted 5° to ecliptic plane. –So we have about two eclipse seasons each year, with a lunar eclipse at new moon and solar eclipse at full moon.
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Summary: Two conditions must be met to have an eclipse: 1.It must be full moon (for a lunar eclipse) or new moon (for a solar eclipse). AND 2. The Moon must be at or near one of the two points in its orbit where it crosses the ecliptic plane (its nodes).
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Predicting Eclipses Eclipses recur with the 18-year, 11 1/3-day saros cycle, but type (e.g., partial, total) and location may vary.
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