By studying distant galaxies in the 1920s, Hubble made the following important discovery that led us to conclude that the universe is expanding.
A) All galaxies contain billions of stars, and all galaxies have spiral shapes.
B) All galaxies were born at the same time, and all will die at the same time.
C) All galaxies outside the Local Group are moving away from us, and the farther away they are, the faster they're going.
D) All galaxies outside the Local Group are orbiting the Local Group.
E) Galaxies are in motion throughout the universe, with about equal numbers moving toward us and away from us.
C) All galaxies outside the Local Group are moving away from us, and the farther away they are, the faster they're going.
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Which type of nebula is produced when a star, hotter than 25,000 K, excites the gas near it to produce an emission spectrum producing a distinctive pink color?
a. emission nebulae b. H I c. reflection nebulae d. dark nebulae e. spectral type B6
What are the two most important properties of a telescope? Select exactly two responses.
A. light-collecting area B. retinal intensity C. angular resolution D. magnification
Consider the following statement: "Rocky asteroids are found primarily in the asteroid belt and Kuiper belt while icy comets are found primarily in the Oort cloud." What's wrong with this statement?
A) Asteroids are not made of rock. B) Comets are not icy. C) The Kuiper belt contains icy comets, not rocky asteroids. D) The Oort cloud has nothing to do with comets. E) The statement is accurate as written.
A 50-N object falling in air experiences 30 N of air resistance. The net force on the falling object is
A) 0 N. B) 20 N. C) 50 N. D) 80 N.