It is moving farther from the Earth-sun line in space. Each evening, as the moon's orbital motion carries it away from the Earth-sun line, we see more of the moon's day side. Thus the crescent in the west after sunset appears to wax, or grow fatter each evening.

Why do we see a crescent moon?

As the moon continues in its orbit around the Earth, away from the sun, increasingly more of its sunlit surface is visible. This is why the moon sometimes appears as a crescent or half-moon. When it's farther from the sun and visible above the horizon, it's easier to spot during the day.

What causes moon phases?

Moon phases are determined by the relative positions of the Moon, Earth, and Sun. ... Instead, the Moon's phase depends only on its position relative to Earth and the Sun. The Moon doesn't make its own light, it just reflects the Sun's light as all the planets do. The Sun always illuminates one half of the Moon.