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### 27 Cards in this Set

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 The geocentric theory claims that the _______ is at the _______ of the universe. earth, center path among the stars that the sun appears to follow ecliptic a line between the sun and planet will cover equal areas during any equal orbital time Kepler's second law of planetary motion: law of areas Earth's orbit around the sun revolution planet's circular, slightly off-center orbit eccentric During summer in the northern hemisphere, which way is the North Pole tilted? towards the sun number of degrees Earth's axis is tilted 23 1/2 degrees the force holding planets in their orbits gravity (law of gravitation) English mathematician and scientist who formulated the law of gravitation Sir Isaac Newton first person to use a telescope for astronomy Galileo Galilei time required for a planet to orbit the sun is proportional to its distance from the sun Kepler's third law of planetary motion: period-distance relationship German astronomer who formulated the three laws of planetary motion Johannes Kepler Kepler's three laws of planetary motion 1. elliptical orbits 2. law of areas 3. period-distance relationship the sun is one focus of the ellipse Kepler's first law of planetary motion: elliptical orbits the crystal, or transparent, spheres proposed in the geocentric view of the universe deferents Polish astronomer who played the major role in developing the heliocentric view of the universe Nicolaus Copernicus view of the universe which states that the sun is the center and all heavenly bodies revolve around it heliocentric view the seven celestial bodies (excluding the stars) observed by the earliest astronomers sun, moon, Mercury, Venus, Mars, Jupiter, Saturn ancient view of the universe which states that the earth is the center and all heavenly bodies revolve around it geocentric, or Ptolemaic, view the turning of Earth on its axis rotation Kepler's major contribution to Copernican theory elliptical orbits term describing the sun and all other celestial bodies revolving around it solar system tendency of bodies in motion to remain in motion in the same direction at a constant speed inertia imaginary line about which the earth is spinning axis date of the vernal equinox March 21 (may vary a day because of leap year) type of wind patterns that are evidence of Earth's rotation diagonal date of autumnal equinox September 22 (may vary a day because of leap year)