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# ES 2.2 PPT

## by Ryan Cooper on Sep 15, 2010

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## ES 2.2 PPTPresentation Transcript

•  The Earth exhibits two main motions: • Rotation – the turning, or spinning, of a body on its axis. • Revolution – the motion of a body, such as a planet or moon, along its orbit around some point in space. The Earth also has another very slow motion. • Precession – the wobbling of a body around its axis of rotation.
•  The main results of the Earth’s rotation (W to E) are day and night. • Takes about 24 hours moving approx. 1000 mph! • Axis of rotation tilted about 23.5 We can measure Earth’s day in 2 ways: • Synodic (Solar) – one complete rotation with respect to the Sun  24 hours. • Sidereal – one complete rotation with respect to distant stars  23 hours, 56 minutes.
• http://astro.unl.edu/classaction/animations/lunarcycles/synodiclag.html
•  Earth revolves around the Sun in a very slight elliptical orbit. (Kepler’s 1st Law) • Takes 365.25 days traveling at an average speed of 67,000 mph! • Average distance of 93 million miles. However, due to its slightly elliptical orbit, Earth’s distance from the Sun varies. • Perihelion – Earth is closest to the Sun.  91 million miles. • Aphelion – Earth is farthest from the Sun.  95 million miles.
•  Winter Solstice  Summer Solstice • December 21 • June 21 • SDR  23.5 S • SDR  23.5 N (Tropic of Capricorn) (Tropic of Cancer) • 10 hrs. day, 14 hrs. night • 14 hrs. day, 10 hrs. night Spring (Vernal) Equinox  Fall (Autumnal) Equinox • March 21 • September 21 • SDR  Equator • SDR  Equator • 12 hrs. day, 12 hrs. night • 12 hrs. day, 12 hrs. night http://astro.unl.edu/classaction/animations/coordsmotion/eclipticsimulator.html
•  The motion of Earth’s axis • A lot of astronomers link as it traces out a circle on climate change to this. the sky. • Presently, the axis of the Earth points to the star, Polaris Amount of time it takes to (North Star). complete one circle is • In about 13,000 years, it will 26,000 years! point to Vega!
•  Earth has one natural satellite, the moon (Luna), which also makes an elliptical orbit around the Earth. • Due to this, its distance from Earth varies from time to time. • Perigee – moon is closest to Earth. • Apogee – moon is farthest away from Earth. • The motions of the Earth-moon system constantly change in relation to the Sun, Earth, and moon.  This is why the moon appears differently throughout each month.
•  The lunar phases are caused by the changes in how much of the illuminated (sunlit) side of the moon faces Earth. • Half the moon is always illuminated! The moon produces none of its own light.
•  1st Phase  NEW MOON • None of the moon appears illuminated as viewed from Earth. Waxing – phases during which the lit portion of the moon increases from the RIGHT. Waning – phases during which the lit portion of the moon decreases and only the LEFT hand side remains illuminated.
•  Thecycle of the moon through all 8 phases takes 29.5 days. • This is one complete revolution with respect to the sun and is called a synodic month. Thetrue period of revolution for the moon is actually 27.3 days. • This revolution is known as a sidereal month, since it is with respect to distant stars. • The reason it takes longer to go through the phases is because as the moon is revolving around Earth, the Earth-moon system is also revolving around the Sun.
•  Themoon is not only revolving around the Earth, but also rotating upon its own axis. • One complete rotation on its axis takes 27.3 days. • You may recall this number is the sidereal month time. Therefore, the moon revolves around the Earth at the same rate it rotates on its axis. This is called synchronous rotation.
•  Due to the moon’s synchronous rotation, its surface experiences periods of daylight and darkness lasting about 2 weeks each. This, along with no atmosphere on the moon accounts for the temperature extremes of 127 C (261 F) on the day side of the moon and -173 C (-279 F) on the night side.
•  Throughout early astronomy, the Greeks realized shadows on certain celestial bodies such as the Earth and moon. When the moon moves in a line directly between Earth and the Sun, it casts a dark shadow on Earth and is known as a solar eclipse. Occur during the new moon phase, as viewed from Earth.
•  When the Earth is positioned between the Sun and the moon, Earth casts its shadow on the moon, and a lunar eclipse occurs. Occur during the full moon phase, as viewed from the Earth.  On average, there are 4 eclipses each year, 2 of each kind (solar and lunar). The zone of full shadow is known as the umbra. The zone of partial shadow is known as the penumbra.
• A BSolar Eclipse Lunar Eclipse
•  Why doesn’t a solar eclipse occur with every new moon and a lunar eclipse occur with every full moon?  They would if the orbit of the moon lay exactly along the plane of Earth’s orbit around the Sun.  However, the tilt of the moon’s path around Earth is 5 .
•  During a total solar eclipse, the moon completely blocks out the solar disk of the Sun for up to seven minutes. • Temperature sharply decreases a few degrees during this time. • Visible only to people within the moon’s umbra. A partial eclipse is seen by those in penumbra. • Total solar eclipses are very rare at any location. Next one visible from the United States  8-21-17
•  During a total lunar eclipse, the moon is completely within Earth’s umbra, but is still visible as a reddish-orange disk. • This is due to Earth’s atmosphere scattering sunlight.  Longer, red wavelengths reflect • Visible to anyone on the side of the Earth facing the moon.  Total lunar eclipse can last up to almost 2 hours!
•  Our natural satellite, the moon, is about 1/4 the diameter of Earth. • Much of what we know about the moon comes from the Apollo missions.  Six Apollo spacecraft landed on the moon between 1969 and 1972. Gravitational attraction at the lunar surface is 1/6 of that experienced on Earth’s surface. • Example: 150 lb. person on Earth weighs only 25 lb. on the moon.
•  Most widely accepted theory for the origin of the moon is when the solar system was forming, an object the size of Mars impacted the Earth. • Debris was ejected from this collision and eventually entered orbit around Earth, combining to form the moon. • This is known as the Giant Impact Hypothesis.
•  Themost obvious feature of the moon’s surface are craters, which are round depressions in the surface of the moon. • Larger craters are about 250 km. in diameter (width of Indiana). • Most craters were produced by the impact of rapidly moving debris or meteoroids from space.
•  In contrast, the Earth’s surface only has about a dozen easily recognized craters. • Friction with Earth’s atmosphere burns up small Vredefort: 250-300 km. debris prior to making impact with Earth’s surface. Three largest on Earth’s surface include: • Vredefort (South Africa) Sudbury: 200 km. • Sudbury (Canada) • Chicxulub (Mexico) Chicxulub: 170 km.
•  Most of the moon’s surface is made of densely cratered, light-colored areas known as highlands. • They cover most of the surface on the far side of the moon. • The highlands consist of mountain ranges made from lunar material.
•  When Galileo first viewed the moon from his telescope, he noticed dark areas, which he thought looked like seas. • We now term these dark, relatively smooth areas on the moon’s surface maria, which is the Latin for “sea”.  These beds of old lava flows formed when meteoroids punctured the moon’s surface, allowing magma to bleed out.  Long channels called rilles, are associated with maria  may be remnants of ancient lava flows.
•  The first manned mission to successfully land on the moon was the Apollo 11 mission (July 20, 1969) • This mission carried three astronauts: Neil Armstrong, Buzz Aldrin, and Michael Collins.  Of those 3, only 2 walked on the moon (Armstrong first, then Aldrin). Collins stayed in the command module.  This fulfilled President John F. Kennedy’s dream (speech in 1961).