According to common sense, stars are not visible during the day because the bright sunlight overwhelms their faint light.
More technically, this occurs because the atmosphere scatters sunlight, thus blocking out the faint starlight.
Similarly, just as stars are typically invisible during the day, we might expect the moon to be invisible as well. However, the moon can indeed be seen during the day.
Why can we see the moon during the day?
1. The moon is sufficiently bright
We know that the moon itself does not emit light but appears bright due to reflecting sunlight. Interestingly, the moon is actually quite dark, with only about 3% of the sunlight that hits its surface being reflected. Yet, this small amount is enough to illuminate our night sky. Thus, while not as bright as the sun, the moon is much brighter than the brightest stars in our night sky. Consequently, it can be visible in the daytime sky, even at noon.
2. Earth's rotation
The visibility of the moon from Earth depends entirely on its position in orbit. The moon orbits the Earth in just under thirty days, presenting different phases in our sky during this time, commonly divided into eight lunar phases.
During certain periods within this cycle (approximately during the full moon), the moon rises as the sun sets because the moon and the sun appear opposite each other in our sky. Hence, during each full moon, the sun, moon, and Earth align fixedly, allowing us to witness both the sunset and the moonrise (on the opposite horizon) simultaneously.
However, as time progresses, the moon's position gradually shifts closer to the sun until it reaches its closest position, around the time of the new moon when it is almost in line with the sun.
As a result, the moon becomes less visible at night and more noticeable during the day. As the Earth continues to rotate, the moon appears above the horizon for approximately 12 hours, coinciding with the 12 hours the sun spends on the horizon, enabling us to see the moon throughout the entire day.
From that point, the moon gradually moves away from the sun until it returns to the full moon phase, and the cycle begins anew. Interestingly, the moon is visible almost every day during the day (except during the days approaching the new moon), but it requires careful observation to notice. This is why most people do not see the moon during the day regularly.
Following the full moon, until a few days before the new moon, the moon will be visible during the day (it is not visible during the new moon phase because the illuminated side of the moon faces away from Earth). By tracking lunar phases daily, we can determine the exact times when the moon is visible during the day.
Therefore, although it may be surprising to see the moon during the day, this phenomenon has a natural and reasonable explanation. The brightness of the moon and the relative positions of the Earth and the moon contribute to this marvelous sight.
By carefully observing lunar phases, we can better understand the regularity of this phenomenon and appreciate this incredible spectacle in the daytime sky.
