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### 42 Cards in this Set

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 a small circle the center of which moves around in the circumference of a larger circle: used in Ptolemaic astronomy to account for observed periodic irregularities in planetary motions. Epicycle Who discovered the "heliocentric universe"? Copernicus What does a "Geocentric Universe" mean? It means that people used to think that the Earth was the center of the solar system and that everything revolved around it. occurs when the two planets lie in a line on the same side of the Sun inferior conjunction angle btwn the sun and a planet as viewed from the Earth elongation length of time during which a body in the solar system makes one orbit of the sun relative to the earth, i.e., returns to the same elongation. synodic period variation (change) in anle that occurs when viewing a nearby object from different places. parallax The orbit of every planet is an ellipse with the sun at one of the foci. Kepler's 1st law of planetary motion A line joining a planet and the sun sweeps out equal areas during equal intervals of time as the planet travels along its orbit. This means that the planet travels faster while close to the sun and slows down when it is farther from the sun. Kepler's 2nd law of planetary motion The squares of the orbital periods of planets are directly proportional to the cubes of the semi-major axes (the "half-length" of the ellipse) of their orbits. Kepler's 3rd law of planetary motion The distance from us and the Sun is an ___________ _________. astronomical universe distance light travels in one year light year an object in motion stays in motion inertia Newton's 1st law of motion The acceleration of an object is proportional to the force acting on it Force = Mass * Acceleration Newton's 2nd law of motion The ancient Greeks laid the groundwork for progress in science. Early Greek astronomers devised a geocentric cosmology, which placed the _______ at the center of the universe. Earth The _________ method is a procedure for formulating theories that correctly predict how the universe behaves. scientific A scientific theory must be testable, that is, capable of being _________. disaproved Theories are tested and verified by observation or __________ and result in a process that often leads to their refinement or replacement and to the progress of science. experimentation In a heliocentric cosmology, the ______ is but one of several planets that orbit the sun. Earth The _______ orbital period of a planet is measured with respect to the stars. It determines the length of the planets year. Its ________ period is measured with respect to the sun as seen from the moving Earth. Sidereal Synodic _______ describe the paths of the planets around the Sun much more accurately than do circles. Ellipses Galileo The invention of the telescope led ________ to new discoveries, such as the phases of Venus and the moons of Jupiter, that supported a heliocentric view of the universe. _______ based his explanation of the universe on three assumptions now called ________ laws of motion. These laws and his law of universal gravitation can be used to deduce Kepler's laws and to describe planetary motion with extreme accuracy Newton Newton The _____ of an object is a measure of the amount of matter in the object. mass ______ is a measure of the force with which the gravity of some other object pull on the object's mass when the two objects are at rest with respect to each other. weight What makes a theory scientific? A theory is an idea or set of ideas proposed to explain something about the natural world. A theory is scientific if it makes predictions that can be objectively tested and potentially disaproved. What is the shape of the Earth's orbit around the Sun? All planets have elliptical orbits around the Sun. Do the planet orbit the Sun at constant speeds? No. The closer a planet is to the Sun in its orbit, the faster it is moving. It moves fastest at perihelion and slowest at aphelion. Do all the planets orbit the Sun at the same speed? No. A planet's speed depends on its average distance from the Sun. The closest planet moves fastest, the most distant planet moves slowest. How much force does it take to keep an object moving in a straight line at a constant speed? Unless an object is subject to an outside force, like friction, it takes no force at all to keep it moving in a straight line at a constant speed. How does an object's mass differ when measured on Earth and on the Moon? Assuming the object doesn't shed or collect pieces, its mass remains constant whether on the Earth or on the Moon. Its weight, however, is less on the Moon. Who wrote down the equation for the law of gravitation? a. Copernicus b. Brahe c. Newton d. Galileo e. Kepler c. Newton Which of the following most accurately describes the shape of the Earth's orbit around the Sun? a. circle b. ellipse c. parabola d. hyperbola e. square b. ellipse Of the following planet's, which takes longest to orbit the Sun? a. Earth b. Uranus c. Mercury d. Jupiter e. Venus b. uranus What is a sun-centered model of the solar system called? heliocentrism How long does it take the Earth to complete a sidereal orbit of the Sun? 365 and 1/4 days How did Copernicus explain the retrograde motions of the planets? The Copernican model placed the Sun at the center of the universe and the Earth and planets in orbit around the Sun. Retrograde motion is an optical illusion caused by our moving point of view. The outer planets have larger orbits than Earth, so the Earth overtakes, causing the planet to appear to move backward. The inner planets have smaller orbits than Earth, so when they overtake us, they appear to move backwards. Which planets can never be seen at opposition? inferior planets Which planets never pass through inferior conjunction? superior planets At what configuration would it be best to observe Mars, Jupiter, and Saturn with an Earth-based telescope? Superior conjunction At what configuration would it be best to observe Mercury or Venus with an Earth-based telescope? Inferior conjunction Why was the discovery of Neptune a major confirmation of Newton's universal law of gravitation? Because he predicted that there was an 8th planet out there.