Astr100 Midterm Studyguide

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Lecture 13
Lunar Eclipse
* An eclipse in which the moon passes into the shadow of the Earth * Umbra: the portion of the shadow that receives no direct sunlight from the light source * Penumbra: the portion of a shadow that receives direct light from only part of the light source * Eclipse season: the time of year during which a solar or lunar eclipse is possible Types of Lunar Eclipses

* Penumbral Lunar Eclipse: an eclipse where the moon passes through the earth’s penumbra, but not the umbra; last occurred 2/9/09 * Total lunar eclipse: an eclipse when the moon is completely in the earth’s umbra for a portion of the eclipse; last occurred 2/22/08 * Partial lunar eclipse: an eclipse when only a portion of the moon passes through the earth’s umbra Solar Eclipses

* An eclipse of the sun by the moon
* Total Solar Eclipse: eclipse when the sun’s photosphere (or normally visible portion) is completely blocked by the moon * Corona: the outer atmosphere of the sun; only visible during a total solar eclipse * Partial Solar Eclipse: only a portion of the sun is covered by the moon * Annular Solar Eclipse: an eclipse in which the moon is located to far from the earth for the moon to completely cover the sun; the outer ring of the sun is seen as a bright ring or an annulus; occurred last 1/26/09 The interior of the earth

* Average density: ratio of mass to volume; earth’s average density is 5.4g/cm^3 * Seismology: study of the earth’s physical qualities; we know the makeup of the earth’s interior by analyzing two types of waves generated by earthquakes 4 Parts of the Earth’s interior

* Crust: (<100 km) thin, outermost layer of the earth; rocky and has density ~ 2.5-3g/cm^3 * Mantle: (2900km) thick, solid layer between the crust and the Earth’s core. The density of the mantle is 3-9 g/cm^3; the crust “floats” on the mantle * Outer Core: composed of liquid metals; 1800 km thick

* Inner Core: innermost portion w/ density up to 13g/cm^3; composed mainly of nickel and iron * Differentiation: the chemical process responsible for the pattern that density increases inwardly; due to the sinking of denser materials toward the center of the early earth Earth’s Magnetic Field

* Magnetic Field: thought to originate in the Earth’s liquid outer core * Magnetic Axis: are not located at the poles of rotation, rather, the magnetic axis is tipper about 13degrees; magnetic poles change with time * Dynamo Effect: model that explains the earth’s and other planets’ magnetic fields as being due to electric current flowing within molten iron cores Past and Future Reversals of the Earth’s Magnetic Polarity * Magnetized rocks of different ages have revealed that the direction/polarity of the geomagnetic field has reversed 171 times during the past 76 million yrs * Some worry more cosmic rays will hit the earth if the magnetic polarity reverses again Earth’s Magnetosphere

* Magnetosphere: the region where the geomagnetic field of Earths dominates the interplanetary magnetic field * Van Allen Belts: two doughnut shaped regions composed of charged particles from the sun captured by the Earth’s magnetic field; named after discovered James Van Allen of Iowa university who recently passed * Aurorae: patterns of different colors in the atmosphere resulting from disturbances in the earth’s magnetic field where charged particles follow the magnetic field line down into the atmosphere and collide with atoms Lecture 14

Plate Tectonics
* Alfred Wegener: credited with developing the idea of continental drift * Continental Drift: the gradual motion of the continents relative to one another * Lithosphere: comprised of the earth’s crust and mantle’s outer 40 miles; the lithosphere is broken into about 12 tectonic plates * Rift Zone: a place where tectonic plates are being pushed apart, normally by molten material being forced up out of the mantle * Mid-Atlantic Ridge:...
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