physics 5 lecturenotes week 1

physics 5 lecturenotes week 1 - Chapter 4: Motions and Time...

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1 Chapter 4: Motions and Time Constellation Cygnus Moons phases and eclipses Motion of Moon, Earth and Sun Paths in the sky: rising, setting, seasons Time and calendars
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2 Constellation Cygnus Right Ascension: 21 hours Declination: 40 degrees Visible from latitudes 90 to -40 degrees Best seen in September (at 9:00 pm) The Milky Way passes through Cygnus Star Deneb is 18 th brightest in sky
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3 Phases of the Moon view from Earth facing the moon view from space 2 Qs: Where sun. . Stood on moon
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4 Where to find the Moon in the Sky The phase of the moon is a measure of the angle between the Sun and the Moon seen from Earth. (memorize) New moon is in the direction of the sun. Rises and sets about same time as sun. A crescent Moon is farther from sun in our sky than the new moon, but still near the Sun first or last quarter (half Moon) must be overhead when the Sun is rising or setting full Moon rises when the Sun sets, and it is highest in the sky near midnight. North pole
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5 Rising and Setting Imagine you are standing on the Earth’s equator. This is the edge of the Earth in the figure, because the North pole is in the center of the drawn circle. At noon your horizon is the vertical yellow line. As Earth spins counterclockwise, you and your horizon stay fixed on the Earth and spin with the Earth. The 3 rd quarter moon is about to set (Earth should be much smaller, so yellow line touches first and3rd quarter moon) while the first quarter is rising. By 3pm your horizon is the green line. 3Qs: highest in sky. . rise…set?
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6 Lunar Eclipses: Sun-Earth-Moon in line A lunar eclipse occurs when the Moon is in the Earth’s shadow. sees the eclipse. It looks red sunlight is refracted (bent) through our atmosphere. The Moon must be full.
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7 Solar Eclipses: Sun-Moon-Earth in line Solar eclipses happen when the Moon passes between us and the Sun. The Moon must be new. 3Qs: type . .type. . and phase
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8 Eclipses and shadows The Moon happens to have about the same angular size as the Sun. The moon can just completely cover the sun when perfectly aligned. The type of solar eclipse (total, partial, annular) depends on Earth’s position in Moon’s shadow. Memorize!
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9 Total Solar Eclipses The sky dark, stars visible. Lasts few minutes in any one place. Somewhere on Earth: 1 or 2 per year. Q: solar eclipse. . A total (solar) eclipse: sun-moon-Earth in exact alignment.
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10 The Path of totality moves The Moon’s orbit carries the path of totality across the spinning Earth. You will see a total eclipse from the blue regions. From a specific place: centuries between total eclipses movie: www.moonglow.net/eclipse/
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11 Eclipses are not bi-weekly Moon’s orbit is tilted 5 degrees to the Earth-sun line Earth and moon are far apart. Accurate separation for sizes Moon shown too near and too big
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12 The Sky Because the Earth is a sphere, the positions of the stars in your sky, and those at your zenith and horizon depend on where you are on Earth.
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physics 5 lecturenotes week 1 - Chapter 4: Motions and Time...

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