Compared to the Sun, older stars contain what proportion of elements heavier than hydrogen and helium?
A) a higher proportion
B) exactly the same proportion
C) they contain absolutely no heavy elements at all
D) a lower proportion
D
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In what sense do telescopes function as "time machines"?
A) They allow us to observe individual stars and galaxies as they change with time. B) Some of the oldest telescopes are still in use today. C) They allow us to see distant objects as they were in the distant past. D) They allow us to see the Milky Way Galaxy as it was when it was much younger.
When an alpha particle is emitted from an unstable nucleus, the atomic number of the nucleus
A) decreases by 2. B) increases by 4. C) increases by 2. D) decreases by 4. E) increases by 6.
As a projectile thrown upward at a non-vertical angle moves in a parabolic path, as in the figure, at what point along its path are the velocity and acceleration vectors for the projectile perpendicular to each other?
Cosmological redshift is the result of
A) the high speeds at which galaxies move within clusters. B) the expansion of the universe. C) old, red stars in distant galaxies. D) supermassive black holes.