What is one piece of evidence for dark matter?
A. the existence of many dark cool dust clouds that do not emit radiation
B. the presence of neutrinos
C. the existence of many planetary systems
D. the fact that the rotation curves of most galaxies become flat at large distances from the center
Answer: D
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Since brown dwarfs cannot ignite hydrogen fusion, how might we hope to spot them? What role does deuterium play in this?
What will be an ideal response?
Which of the following never appears to exhibit retrograde motion?
A) the Sun B) Venus C) Mars D) Jupiter E) Saturn
An infinite universe is one of the assumptions of the cosmological principle
Indicate whether the statement is true or false
What makes us think that Mars must once have had an atmosphere that was warmer and had higher surface pressure?
A) We think it for purely theoretical reasons, based on calculations showing that the Sun has brightened with time. B) The atmosphere is too cold and thin for abundant liquid water today, yet we see evidence of large areas of flowing water in the past. C) The presence of inactive volcanoes on Mars tells us that there must once have been a lot of outgassing, and hence a thicker atmosphere. D) The fact that parts of Mars have a lot of craters tells us that Mars must once have been much warmer.