Prepared by Lisa M. Will, San Diego City College Lecture Slides CHAPTER 2: Patte
Conrad, Rob, Morning Drive-Time Personality has reference to this Academic Journal, PHwiki organized this Journal Prepared by Lisa M. Will, San Diego City College Lecture Slides CHAPTER 2: Patterns in the SkyMotions of Earth in addition to the Moon Underst in addition to ing Our Universe SECOND EDITION Stacy Palen, Laura Kay, Brad Smith, in addition to George Blumenthal Patterns in the Sky What do we observe on the sky due to the: Rotation of Earth Revolution of Earth Axial tilt of Earth Orbit of the Moon Rotation of the Earth One day is 24 hours. One rotation with respect to stars = 23 hr 56 min = sidereal day One rotation with respect to the Sun = 24 hours = solar day Earth rotates counterclockwise in addition to also orbits the Sun in the counterclockwise direction.
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Class Question The Sun rises in the east in addition to sets in the west. Which way is Earth rotating Toward the west Toward the north Toward the east Toward the south Celestial Sphere The celestial sphere is a projection of Earths axes in addition to equator into space. The celestial sphere rotates around the north in addition to south celestial poles each day. Celestial Sphere: Celestial Equator in addition to Ecliptic Celestial equator: midway between the two poles. Ecliptic: apparent path of the Sun, inclined 23.5 degrees to equator.
Celestial Sphere: Earths North Pole At Earths North Pole, we would see half of the celestial sphere. The north celestial pole would be at the zenith, the point directly overhead. Celestial Sphere: Circumpolar No star rises or sets =>circumpolar. Observers never see the south celestial pole. Celestial Sphere: Circumpolar (Cont.)
Celestial Sphere: Circumpolar (Cont.) Celestial Sphere: Circumpolar (Cont.) From what location on Earth would all of the stars on the celestial sphere be visible Equator North Pole Prime Meridian South Pole Class Question
Celestial Sphere: Hemispheres At Earths equator, all stars rise in addition to set. The celestial poles are on the northern in addition to southern horizons. What would the sky look like from a latitude of 30° N All stars would be circumpolar. All stars would be visible. No stars would be visible. Some stars would be circumpolar; some would never be visible. Class Question Celestial Sphere: Stars Visibility Some stars are circumpolar. Some stars are never visible.
Revolution of the Earth The average distance to the Sun is called the astronomical unit, or AU. 1 AU = 150 million km = 8.3 light-min Revolution of the Earth: Zodiac As Earth revolves, the Sun is seen against different constellationsthe zodiac. The constellations are along the ecliptic. Axial Tilt of the Earth Earths axis is tilted at an angle of 23.5°with respect to the ecliptic plane.
Axial Tilt of the Earth: In Summer The tilt causes the seasons. In summer: The angle of sunlight is more direct. Energy is more concentrated in addition to days are longer. Axial Tilt of the Earth: In Summer (Cont.) Axial Tilt of the Earth: In Summer (Cont.)
Axial Tilt of the Earth: Summer in addition to Autumnal Seasons Summer solstice: Sun is at its highest point above the ecliptic (June 21). Longest day. Autumnal equinox: Sun on the celestial equator (Sept. 22). Equal hours of day in addition to night. Axial Tilt of the Earth: Winter in addition to Vernal Seasons Winter solstice: Sun at its lowest point below the ecliptic (December 21). Shortest day. Vernal equinox: Sun on the celestial equator (March 20). Equal hours of day in addition to night. Axial Tilt of the Earth: Winter in addition to Vernal Seasons (Cont.)
Axial Tilt of the Earth: Winter in addition to Vernal Seasons (Cont.) If the ecliptic were aligned with the celestial equator, what would happen to the seasons Each season would last longer. Nothing. They would be the same as now. We would not have seasons at all. Cannot tell from the in as long as mation given. Class Question Axial Tilt of the Earth: Changes Over Years Earths axial tilt changes orientation over a period of 26,000 years due to precession. The location of the poles slowly shifts. Currently the north celestial pole is near the bright star Polaris.
Orbit of the Moon Synchronous rotation. The Moon completes one full rotation in one full revolution around Earth. Orbit of the Moon: Moon From the Earth The Moon shines because of reflected sunlight. Half of the Moon is always illuminated by the Sun. Phases of the Moon The phase of the Moon is determined by how much of the bright side we see.
If Earth rotated in 12 hours but its orbit were the same, which of the following would NOT be true Each season would happen twice per year. We would still see only one hemisphere of the Moon. The cycle of lunar phases would last as long as it does now. Observers at the North Pole would only see one half of the celestial sphere. Class Question Chapter Summary The daily patterns of rising in addition to setting => Earths rotation. The annual patterns of the stars in addition to constellations in the sky => Earths revolution. The changes in the length of day in addition to intensity of sunlight that create the seasons => Axial tilt of the Earth. The phases of the Moon => Moons revolution around the Earth.
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