Moon in Broad Daylight: Here's Why We Can Sometimes See Earth's Natural Satellite in the Daytime Sky

The Sun and the Moon usually share the daytime sky, but why is this the case?

The only times when the daytime Moon cannot be visible is when it is near Full Moon and New Moon.

Daytime Moon

The reason why people may see the Moon during the day is the same reason why they may see the Moon during the night. This is due to how the Moon reflects the light of the Sun.

Moreover, the Moon's closeness to the Earth ends up making it brighter compared to the nighttime or daytime sky. The Moon is the second-brightest cosmic object that can be seen from Earth, coming after the Sun.

However, the moon is not visible during the day. This is due to the atmosphere of the Earth and the Moon's orbital cycle.

If the Earth did not have any atmosphere, the Moon would always be visible.

Moreover, the lunar phases mean that if it moves in between the Earth and the Sun, the illuminated side does not face Earth, while the Moon's dark side does not face the planet. This makes it invisible to Earth skywatchers.

Visible Moon in Broad Daylight

The atmosphere's gas particles, which are mainly oxygen and nitrogen, scatter light with a short wavelength, such as violet and blue light. Such scattering covers the absorption and re-emission of light in another direction and is the reason why the sky is blue.

For the Moon to be visible during the day, it needs to overcome such scattered light. For two to three days around the New Moon, the natural satellite is invisible to Earth observers. Its sky position would mean that the scattered light of the Sun outshines the Moon.

However, usually, the relative closeness of the Moon with the Earth, which is an average proximity of 384,000 kilometers, implies that the light reflected looks brighter compared to objects that emit or reflect light that are farther away.

Edward Guinan, an astronomy and astrophysics professor from Villanova University, said that the stars that can be seen from Earth are a "million billion times less bright" compared to the Sun's light. Moreover, they are also a million times fainter compared to the brightness of the Moon.

The Sun's scattered light is so bright in the sky that it overwhelms starlight during daytime. However, it does not always overwhelm the reflected light of the Moon.

Astronomers make use of surface brightness to quantify objects' apparent brightness within the sky. They do so by measuring the light amounts emitted across a night sky area.

Because the Moon is more proximate to the Earth compared to stars, its surface brightness is greater compared to that of the sky. This means that it is easy for humans to see the Moon shine during the day.

However, there are also other factors that can affect the visibility of the daytime Moon. These include the current lunar phase, the seasons, and the clearness of the sky on any day.

On average, the Moon is visible during the day for 25 days out of the month all throughout the year. The remaining five days take place around the Full Moon and New Moon lunar phases.

During the New Moon lunar phase, the Moon would be too close to the Sun for it to be visible. When it is near a Full Moon, its visibility is only possible during the night, as the Moon goes up at sunset and sets during sunrise.

Moreover, though the Moon is hovering over the horizon for 12 hours a day, its visibility may not always match with daytime hours. During winter, when mid-latitude days are shorter, the Moon has a shorter time for daytime visibility. Earthshine can also affect lunar visibility.