A comet's nucleus is composed of:
A. dust, dry ice, and water ice.
B. methane and hydrocarbons
C. just iron
D. gases, including mostly hydrogen and helium.
E. iron and silicates.
Ans: A. dust, dry ice, and water ice.
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How is the sunspot cycle directly relevant to us here on Earth?
A) Coronal mass ejections and other activity associated with the sunspot cycle can disrupt radio communications and knock out sensitive electronic equipment. B) The sunspot cycle strongly influences Earth's weather. C) The Sun's magnetic field, which plays a major role in the sunspot cycle, affects compass needles that we use on Earth. D) The brightening and darkening of the Sun that occurs during the sunspot cycle affects plant photosynthesis here on Earth. E) The sunspot cycle is the cause of recent global warming.
Early astronomers used models showing that the Earth was at the center of the universe. Why did they feel this was true?
How long does it take for a radio signal to travel to a spacecraft 
m away?
A. 5.0 s
B. 50 s
C. 
D. 
E. 
Protoplanets
a. grew in size primarily by accretion. b. grew in size primarily by condensation. c. are still visible today as the terrestrial planets. d. grew in size by collecting the particles in the solar wind. e. grew in size by the collision and coalescing of planetesimals.