The expansion of a star to giant or supergiant size _____, and so the stars move toward the upper right in the Hertzsprung-Russell (H-R) diagram
A) contracts the star drastically
B) cools the star's outer layers
C) dims the star
D) makes the star less luminous
B
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____ about 130 km above Earth's surface near the polar regions when energy in the solar wind guided by Earth's magnetic field excites gases in the upper atmosphere
a. Coronas occur b. Flares occur c. Auroras occur d. Coronal holes occur e. Nuclear fission occurs
Bert says that a charged particle in a vacuum can travel in a helix only if a uniform electric field and a uniform magnetic field are both present and both parallel to the axis of the helix. Stuart says that only a magnetic field with a component parallel to the axis of the helix is needed. Which one, if either, is correct, and why?
a. Bert, because the charged particle's velocity can have a vertical component only if an electric field in the vertical direction is present. b. Stuart, because a component of velocity in the vertical direction is not changed by a vertical component of a magnetic field. c. Bert, because a component of velocity in the vertical direction is changed by a vertical component of a magnetic field. d. Stuart, because an electric field in the vertical direction would cause the particle to come to a complete stop. e. Neither, because particles cannot move in helical paths in the presence of magnetic and electric fields.
Why is 21-cm radiation so important to the study of interstellar matter and the Galaxy?
A) It helps locate the galactic core in Sagittarius. B) Emitted by hydrogen, it passes through interstellar dust and lets us to map the entire Galaxy. C) Emitted by carbon monoxide, it passes through interstellar gas and lets us to see places rich in organic molecules around the Galaxy. D) It is emitted by most stars, enabling astronomers to map the entire Galaxy. E) It is emitted only in hot regions of star formation, so the pattern of the spiral arms of the Galaxy can be mapped.
Periods are divided into
a. eons. b. epochs. c. millennia. d. eras.