Transcript Document
Where did the solar system come from? Also: Sun – Moon -Eclipses Astr 221 2015 NW Chs. 8&9 Evidence from Other Gas Clouds • We can see stars forming in other interstellar gas clouds, lending support to the nebular theory. 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. Earth Earth and Moon with sizes shown to scale • An oasis of life • The only surface liquid water in the solar system • A surprisingly large moon Giant Impact First Quarter Second Quarter Formation of Lunar Maria Early surface Large impact is covered crater with craters. weakens crust. Heat buildup allows lava to well up to surface. Cooled lava is smoother and darker than surroundings. Radius: 6.9 108 m (109 times Earth) Mass: 2 1030 kg (300,000 Earths) Luminosity: 3.8 1026 watts Gravitational equilibrium: Energy supplied by fusion maintains the pressure that balances the inward crush of gravity. What is the Sun’s structure? Insert TCP 6e Figure 14.3 The proton–proton chain is how hydrogen fuses into helium in Sun. Sunspots Are cooler than other parts of the Sun’s surface (4000 K) Are regions with strong magnetic fields Loops of bright gas often connect sunspot pairs. Insert TCP 6e Figure 14.21a unannotated The number of sunspots rises and falls in an 11-year cycle. Insert TCP 6e Figure 14.21b unannotated The sunspot cycle has something to do with winding and twisting of the Sun’s magnetic field. Magnetic activity also causes solar prominences that erupt high above the Sun’s surface. Charged particles streaming from the Sun can disrupt electrical power grids and can disable communications satellites. Aurora Borealis What causes eclipses? • The Earth and Moon cast shadows. • When either passes through the other’s shadow, we have an eclipse. Lunar Eclipse When can eclipses occur? • Lunar eclipses can occur only at full moon. • Lunar eclipses can be penumbral, partial, or total. Solar Eclipse When can eclipses occur? • Solar eclipses can occur only at new moon. • Solar eclipses can be partial, total, or annular. 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. 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). Predicting Eclipses • Eclipses recur with the 18-year, 11 1/3-day saros cycle, but type (e.g., partial, total) and location may vary.