Everyone knows in general how things seem to work for day and night. During the Day the Sun is the brightest thing there is. We also know that Moon is the brightest object in the sky at night, but wait a minute. Why can we see the Moon during the day as well? The reason is due to two big factors are the moon’s brightness and its orbit around the Earth. These two things make it possible for the moon to still be seen during the day. Otherwise the belief of the Sun by day and Moon by night would still hold.
The Moon is the brightest object in the sky after the sun. The first reason why is that it is so close to Earth when compared to anything else. The Sun is bright because it is burning vast amounts of hydrogen so it really doesn’t need as much proximity to the Earth to be seen. The Moon’s nearness makes it hard to ignore even during the day. The second reason is its reflectiveness. Most of us know the moon is not a smaller sun or star. It is basically a natural satellite that is 1/6th the size of Earth. However, most of the surface is white making it very reflective. In essence the Moon is basically a big mirror reflecting back the Sun’s light from the other side of the Earth.
The other reason is the Moon’s orbit around the Earth. While for the most part the moon seems to set in the West as the Sun rises in the East, this is not always the case. This is because to the attentive observer the Moon is not in the same place all the time. The fact is that during the lunar cycle it makes a circuit across the sky. At the full Moon the moon is exactly opposite of the Sun. However as it gets closer to the New Moon, the Moon gets closer to the sun. This may make the moon less visible at night but it sure makes it more visible in the day.
So that is why we can see the moon during the day. The moon is highly reflective and close to the Earth so it is very visible both day and night. Its orbit increases its visibility because the Moon gets close to the sun towards the beginning of the lunar cycle as travels around the sky. So it increases visibility during the day.
We’ve also recorded an entire episode of Astronomy Cast all about the Moon. Listen here, Episode 113: The Moon, Part 1.