Question

why are there two high tides a day about 12 hours apart from each other?
earth revolves around the sun once during that time.
earth rotates entirely on its axis once during that time.
the moon revolves around earth once during that time.
the moons orbit is in line with earths orbit twice a day.

Explanation:

Tides are mainly caused by the gravitational pull of the Moon on Earth. As Earth rotates on its axis (a full rotation takes about 24 hours), different parts of Earth pass through the areas of high - tide (caused by the Moon's gravitational pull). Since Earth rotates once in about 24 hours, and there are two high - tide areas (one on the side of Earth closest to the Moon and one on the opposite side due to centrifugal force), the time between two high tides is approximately 12 hours. Earth's rotation on its axis is the key factor here. Earth's revolution around the Sun (takes about a year) and the Moon's revolution around Earth (takes about a month) are much longer - term motions and not related to the 12 - hour high - tide cycle. The statement about the Moon's orbit being in line with Earth's orbit twice a day is not relevant to the high - tide cycle.

Answer:

Earth rotates entirely on its axis once during that time.