Which of the following best describes the Milky Way Galaxy?
A) a spiral galaxy with a disk about 100,000 light-years in diameter and containing between 100 billion and 1 trillion stars
B) a spherically shaped collection of stars including our solar system and about a dozen other solar systems, stretching about 4 light-years in diameter
C) a spherically shaped collection of about 1 million stars that is about 100 light-years in diameter
D) a spiral galaxy with a disk about a billion kilometers in diameter and containing between 100 million and 1 billion stars
E) a spiral galaxy with a disk about 100,000 light-years in diameter and containing about 100,000 stars
A
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Why should galaxy collisions have been more common in the past than they are today?
A) Galaxies were closer together in the past because the universe was smaller. B) Galaxies attracted each other more strongly in the past because they were more massive; they had not yet turned most of their mass into stars. C) Galaxies were more active in the past and therefore would have collided with each other more frequently. D) Galaxies were much bigger in the past since they had not contracted completely.
The highest energy level in an atom corresponds to n = 1
Indicate whether the statement is true or false
When a 60-Hz voltage is applied to a 22-?F capacitor, the capacitive reactance is
A) 121 ?. B) 760 ?. C) 13 × 10-4 ?. D) 510 ?. E) 83 × 10-4 ?.
It is very cold, but otherwise comfortable. You breathe deeply. Although there is no oxygen, the air pressure is quite tolerable and seems almost Earth-like (because it is mostly nitrogen)
Your vista includes the breathtaking sights of an ocean of liquid methane and methane-snow-capped mountains (although the atmosphere is very smoggy, and the visibility is limited). Your solar day is about 16 Earth days long. A large, ringed object seems to hang in your sky, never rising or setting; however, it does go through phases from new to full and back to new again with the same 16-day period as the rising and setting of the Sun.