For finding the distance to M31, Hubble relied upon:
A) RR Lyrae stars in its globular clusters.
B) type I supernova in its core.
C) type II supernova in its spiral arms.
D) Cepheid variables in its spiral arms.
E) planetary nebulae near its core.
D
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Claudius Ptolemy created a mathematical model of the Aristotelian Universe in which a planet followed a small circle called the _____ that slid around a larger circle called the deferent
A) heterocycle B) epicycle C) pericycle D) hemicycle
Label 1a lies on the rim of a large crater, and label 1b lies on the rim of a smaller one. Which crater must have formed first?
A) crater 1a B) crater 1b C) cannot be determined
Martian volcanoes are larger than volcanoes on Earth because
A) Mars's weaker gravity makes it easier for tall structures to be built up. B) the lack of plate tectonics on Mars means that mantle plumes remain stationary relative to the surface, building up huge, single mountains. C) Mars has more internal heat than the Earth so volcanoes naturally grow to much larger sizes D) Both A and B
Current in a conductor can be increased by
A) increasing the voltage across it. B) reducing its resistance. C) both of these D) neither of these