Answer:
A. increased; Great Migration
Explanation:
When the migration began, 90 percent of all African-Americans were living in the South. By the time it was over, in the 1970s, 47 percent of all African-Americans were living in the North and West. A rural people had become urban, and a Southern people had spread themselves all over the nation.
<span>Seismic waves.................</span>
<span> the answer is 85,231 mi²</span>
The answer is the spring equinox
Answer:
b. flat rotation curves in spiral galaxies
Explanation:
Dark matter accounts for majority of the matter in the universe (about 85%). It is considered to be composed of subatomic particles which are yet to be discovered. Dark matter cannot be observed because it does not emit light that can be detected. Only its gravitational effect is visible.
Astronomers when calculated the mass of the visible matter and tried to account for the observed speed of stars in the galaxy, there was a mismatch. To understand what caused this mismatch, astronomers gave name to the invisible matter as the Dark Matter.
The expected velocity of stars should decrease away from the near the center of the galaxy but a constant velocity of stars was observed that is a relatively flat rotation curve was obtained.
Thus, flat rotation curves in spiral galaxies in an evidence of Dark Matter.
