Answer:
Correct answer is A. Islamic calendar.
Explanation:
A is correct as this answer known as Hijra happened in 622. This year marks the period from when the Muslims started counting time.
B is not correct as Medieval period starts with the fall of Western Roman Empire.
C and D are not correct as this don't refer to the Muhammed's move from Mecca to Medina.
Our solar system is heliocentric, which means everything revolves around the sun. Geocentric would mean everything revolved around the earth.
Glaciers begin to form when snow remains in the same area year-round, where enough snow accumulates to transform into ice.
Answer: is constant
Explanation:
In order to analyze the velocity of the stars within a galaxy, the <u>galaxy rotation curves</u> (developed by the American astronomer Vera Rubin) are used. These graphs are elaborated as a scatter diagram in which the orbital velocity of the stars present in a galaxy is represented on the Y axis and the distance of these stars to the center of the galaxy on the X axis.
Thanks to this diagram, it has been possible to observe a characteristic behavior in the rotation speed of the stars (and gas) present in the galaxies, which differs from the rules of the orbital movement of the planetary systems postulated by Newton and Kepler.
This means that in these galaxy rotation curves it has been observed that the rotation speed of stars and gas is "constant", regardless of the distance to the center of the galaxy. This discrepancy and these results were then used to demonstrate the existence of dark matter in the universe.
Answer:
none
Explanation:
all i could see was blue sky
