Why does the moon have such an effect on earth's tides and not the sun?

Answer 1

Actually, the sun does affect the earth's tides. The moon and the sun work together to form the tides. When the moon or the sun pull on the earth's oceans, they form an oval shape with 'bulges' on opposite sides of the earth. Those bulges are high tide; the stretched-thin parts are low tide.

When the moon is opposite of the sun (full moon; opposition), the gravity of both the sun and the moon combine to pull even harder on the oceans in opposite directions, thus increasing the bulge and generating spring tides. However, during first quarter or third quarter (half-full moon; the moon is at a 90-degree angle to the sun as viewed from above), the solar force and the lunar force partially cancel each other out, making the tides smaller - these are called neap tides.

The reason that the moon is the predominate player in earth's tides is simply because of its proximity, and its size relative to the earth. The sun, while being many times more massive (and thus, having many times more gravity), is much farther away, so its effect largely mediates the lunar effect.