Moon Visuals Moon11-19-02b.jpg Limb5-11-2003.jpg moon_crater.jpg simple_moon_spin.avi Chapter 9: The Moon, Earth s Satellite Vital Statistics Orbital distance 384,400 km Orbital period 27.32 days Sidereal Month [fig9.1] Cycle 29.53 days Synodic Month Diameter 3476 km Density 3.34 x density of water 1 The Moon has Synchronous Rotation [Figure 9-2, moon_rotation.mov] Rotation (about axis) equals revolution about earth => same side of moon always faces earth =>on the moon, the earth is nearly in the same spot in the sky [fig 9.3] Orbit [ Figure 9.4] inclined ~ 5º Nodes: points where moon s orbit crosses ecliptic Eclipses: (note actual scale of size and separation [fig9.27,eclipser_shadowsb_2010_v2.mov]) Solar Eclipse: from moon s shadow [eclipser1.avi, eclipser2.avi, fig 9.13, fig 9.9-11,eclipses.mov, Eclipses_Nav.swf] may occur during new moon [fig 9.12, 14] total vs partial vs annular [fig 9.10 ] Things to see during a solar eclipse: Baily s Beads (sunlight through lunar valleys) [fig 9.5] Solar Corona: outer region of sun s atmosphere, usually lost in glare [fig 9.7] Solar Prominence [fig 9.8] 2
Lunar Eclipses: due to Earth s shadow occur during full moon total vs. partial [Figure 9-10] Comparison : [Figure 9-12] Umbra Penumbra Everyone can see a lunar eclipse, only those in the shadow can see the solar eclipse. [fig 9.13] Prediction of Eclipses [Figure 9-14,16] 3 Tidal Effects [tides.avi, Figure 9-17] Earth s Rotation drags tidal bulges around faster than moon orbits. Friction effects earth s rotation is slowing! Moon is dragged along by tidal bulges the Moon s orbit is getting larger. Moon s orbit was much closer. 4
The Moon s Surface [ fig 9.18 (da vinci),19 (galileo), 20 (modern), 23] Craters [fig 9.21, 22] most are impact of meteorites some are volcanic Regolith: blanket of rock accumulated debris of meteorites Maria (seas): darker regions from volcanic activity, filling large impact craters terrae (land): lighter regions Rilles [fig 9.24] resemble dried river beds 5 Lunar Samples similar to silicate rocks on earth absence of water, other volatile substances Age terrae ~ older than 4 Billion years maria ~ 3.2-4 Billion years age and cratering [fig 9.25] crater density indicates age crater saturation: impacts wipe out as many craters as are created. light colored terrae less dense than dark maria (basalts) (less dense than average density) => differentiation 6
History of the Surface of the Moon [fig 9.26] Molten (differentiation) Crust Solidification Heavy Cratering ~ 4 Billion Years Formation of basins (future maria) Cratering lessens, maria fill~ 3.8-3.2 Billion Years Crater density age relationship used to estimate age of other solar system objects 7 Moon s Atmosphere thin, nearly non-existent solar wind escaped radioactive decay products low escape velocity most molecules escape into space solar wind strips some of remainder poor insulation extreme temperatures 400 K (250 ºF) - 100 K (-280 ºF) 8
Moon s interior Mass 1/81 x Earth Density 3.3 x water compare Earth (5.5 x water), iron (8 x water) similar to density of earth s crustal and mantle material Little Seismic activity Structure [Figure 9-28] Thicker crust (compared to Earth s) Deep Lithosphere (solid outer region) (possible) small iron core lopsided Contrast Earth: evolving world (atmosphere, surface, interior) Moon: dead world (negligible atmosphere, inactive surface and interior) 9 Origin of the Moon [Figure 9-29] Fission but: why was Earth rotating so rapidly but: orbit should be along equator Binary Accretion but: different chemical makeup (lack of iron in moon) Capture but: excess energy but: chemical similarity between Moon and Earth s mantle Giant Impact [Figure 9-30] most widely accepted -moon's chemical makeup -moon's history 10