The Moon, as we all know, does not shine by its own light. When we see the Moon, it is only because we are seeing the reflection of sunlight reflected off its surface. We can see the Moon in the daytime when the Sun and the Moon are located in the same direction in the sky. As the Moon proceeds on its 29-day orbit around the Earth, at times it is on the opposite side of the Earth from the Sun. The Earth is also spinning on its axis once every 24 hours, a much shorter time than it takes the Moon to revolve around us or for the Earth or Moon together to orbit around the Sun. Though we perceive Moon as rising and setting as it ‘moves’ across the sky, it’s really the Earth rotating on its axis that causes this effect. In one day, the Moon doesn’t move much relative to the Sun or to the Earth, even though during these 24 hours, we see a complete cycle of day and night because of our planet’s spinning.
Viewing of the Moon is also contingent on the state of the Earth’s atmosphere. The stars are ‘out’ during the day. We can not see them because of the scattered light from the stars. But the Moon is the second brightest object in our sky, next to the Sun, so even though it appears pale, we can usually see it during the day if it is close in direction to the Sun. But on days with excessive glare or cloudiness, the Moon may not be visible, especially just before and after a new Moon. Even though the Moon and Sun often appear to be close together, the Sun is always about 400 times farther away from Earth than the Moon is. We can see the Moon during the daytime when the Sun and Moon are relatively close in direction, but not too close! When they are aligned too closely, we can not see the Moon because the Sun is directly behind it and can not light up the side of the Moon facing us. When they are in opposite directions, in the daytime, the Sun is overhead, but the Moon is on the opposite side of the Earth.
When the Moon is overhead, we do see it, but it is night because the Sun is on the other side of the Earth. It’s when the Moon and Sun are at right angles, or close to it, that we can best see the Moon during the day. The Sun, Moon, and Earth form a big triangle, and the Sun is ‘in front’ of the Moon to light up its side that is visible to us, and it’s daytime because the Sun is up in the sky above us.
To get clearer picture, let us assume the Sun as a large light bulb, and the Moon as a large mirror. There are situations where we can not see the light bulb, but we can see the light from the bulb reflected in the Mirror. This is the situation when the Moon is out at night. We can not see the Sun directly because the Earth is blocking our view of it, but we can see its light reflected from the Moon. However, there are also situations where we see both the light bulb and the mirror, and this is what is happening when we see the Moon during the day.