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Unformatted text preview: Chapter 1 I) 1.1 Prehistoric Astronomy A) The Celestial Sphere- All stars lie on a celestial sphere that completely surrounds the earth, with the earth at its center- The line where the sky meets the ground, and below which your view of the celestial sphere is blocked, is called the horizon- The celestial sphere served as a model of the heavens B) Constellations- Fixed patterns of stars on the celestial sphere- Resemble animals using a little imagination C) Motions of the Sun and Stars 1 Daily or Diurnal Motion- As the celestial sphere spins, the north and south celestial polls do not move- The north celestial pole always marks the direction of true north- The celestial equator lies directly above the earth’s equator- Different stars are visible at different times- As the earth moves around the sun, the sun’s glare blocks our view of the part of the celestial sphere that lies toward the sun, making the stars that lie beyond the sun invisible 2 The Ecliptic- The line that the sun traces across the celestial equator- The name ecliptic arises because only when the new or full moon crosses this line an eclipse occur D) The Seasons- The earth’s rotation axis runs through the north and south pole- It is not perpendicular to the orbit around the sun- The tilt is constant causing more sunlight to fall on the northern hemisphere during summer and less during winter 2 The Ecliptic’s Tilt- The sun is high in summer and low in winter 3 Solstices and Equinoxes- Equinox: the days and nights are of equal length Spring (Vernal): March 21 Fall (Autumnal): September 21- Solstice: the sun has stopped its motion north or south June 21 December 21 4 The Planets and the Zodiac- The planes always move within a very narrow band on the celestial equator- All the planets orbits lie nearly in the same plane- The Stars and planets always rise in the east and set in the west- The Planets move in a retrograde motion 5 The Moon- Seems to change throughout the month- As it moves around us we see different amounts of the illuminated half E) Eclipses- Solar Eclipse: the moon passes directly between the earth and the sun- Lunar Eclipse: the earth passes directly between the moon and sun II) 1.2 Early Ideas of the Heavens: Classical Astronomy 1 The Shape of the Earth- Early Greeks knew the earth was round- Aristotle presented arguments that it was round 2 Size of the Earth- Eratosthenes made the first measurement of the earth’s size- Estimated it to be about 25,000- Used angles of shadows on the equinox 3 Distance and Size of the Sun and Moon- Aristarchus of Samos had estimated the relative size of the sun, earth, moon, and distance to each- His calculation of the moon was accurate though- Everything else was wrong- Aristarchus – the sun was the center of the heavens Problems with this were stars should appear in different parts of the sky during different times of the month- Parallax – stars a so remote that the shift is too small to be seen by the naked eye 4 Motion of the Planets...
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This note was uploaded on 04/03/2008 for the course ASTRO 101 taught by Professor Marshall/thornley during the Spring '08 term at Bucknell.
- Spring '08