f10_sep09 - Thurs., Sep. 9, 2010 What causes eclipses? The...

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Thurs., Sep. 9, 2010 Motions & Cycles of the Moon and Planets Lunar and Solar Eclipses The Greeks’ Geocentric Model Copernicus’ Heliocentric Model Properties of Elliptical Orbits What causes eclipses? • The Earth and Moon cast shadows. • When either passes through the other’s shadow, there is an eclipse . • The Sun is fully blocked in the umbra , but only partially blocked in the penumbra . Types of Lunar Eclipses Lunar eclipses can occur only at full moon (but don’t occur at every full moon). Lunar eclipses can be penumbral , partial , or total . The next total lunar eclipse will be on Dec. 21, 2010. It will be visible from Austin.
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Types of Solar Eclipses Solar eclipses can occur only at new moon (but do not occur at every new moon). Solar eclipses can be total, partial , or annular . There were two solar eclipses in 2010, but there will be no more total solar eclipses until Nov. 2012. Solar Eclipses Condition for a Total Eclipse In order for a nearer object to fully eclipse a more distant object, the angular size of the nearer one must be at least as large as the angular size of the more distant one: " near (") = 206,265 # Diam dist $ % & ' ( ) near * far (") = 206,265 # Diam dist $ % & ' ( ) far We’re already considered this phenomenon and applied it to, for example, Phobos and Mars (HW 1). When an object of relatively small angular diameter passes in front of a larger object, it is called a “transit.”
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f10_sep09 - Thurs., Sep. 9, 2010 What causes eclipses? The...

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