Why we see the Moon during the day

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The Moon has always been in the sky since mankind took its first steps on Earth, being an important part of almost all cultures that have developed. Within some mythologies and general culture, the Sun and the Moon are currently considered as opposites and representatives of day and night respectively, however, this is a great oversimplification, since the second is not always visible and does not appear only when our star is not there.

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Panoramic image in which the Sun and the Moon appear in the same capture. Taken from r/pics.

A natural satellite

The Earth orbits the Sun and the Moon orbits the Earth, in both cases elliptical trajectories are respected, that is to say, flattened circumferences. In the first case there is a periodicity; the time it takes to complete one revolution, of approximately 365 days. While the second requires 27 days and the Earth of 24 hours to complete a full rotation around itself..

Knowing these numbers, one can build a mental picture of how the movement of the stars in the sky works, which have been measured with great precision directly or indirectly with numerous instruments improved day by day.

Lunar cycle

The Moon in its translation always keeps one side pointing almost perfectly towards the Earth, thanks to a phenomenon known as tidal coupling. The region that is directly illuminated by the Sun changes as it moves in its orbit, and this movement gives rise to what we know as lunar phases.

Moon phases 00
Diagram with the phases of the Moon, showing the entire cycle between New Moon and New Moon. Given the Earth's translational motion around the Sun, to complete the cycle requires 2 extra days of the Moon's normal orbital period.

The phase in which the Moon is observed from the Earth depends directly on the relative position of the Moon and the Sun in the sky. When both are almost at opposite points it can be observed completely illuminated, this is called Full Moon and the night reigns, making it difficult for both stars to be visible at the same time.

Throughout its journey around the Earth, the illuminated area slowly decreases, passing through the waning, waning, waning and waning gibbous phases. After a little more than 14 days the Moon has moved in the sky, with respect to the sun, and seen from the Earth it is almost imperceptible because we are only seeing the non-illuminated part. This last one is called the New Moon, and after it the process repeats itself, passing through crescent, crescent and crescent gibbous until it is Full again.

The Moon by day

From the lunar phases it is possible to know the relative distance between the Moon and the Sun in the sky. During a Full Moon this is maximum; going out as soon as our star is hidden, and in New Moon it is minimum; being visually very close both stars. On the other hand, in the waxing and waning phases both objects are visible simultaneously during the day. Now, every time you look at the sky, you can remember the incredible orbital dance that gives us beautiful sights day by day.

Francisco Andrés Forero Daza