• There is always one half of the Earth which is illuminated and the other half which remains in the shadows, according to our partner The Conversation.

  • The Moon, on the other hand, revolves around the Earth.

    So it is sometimes opposite the Sun, sometimes on the same side as it.

  • This analysis was conducted by Yaël Nazé, astronomer at the Institute of Astrophysics and Geophysics of the University of Liège (Belgium).

To answer this question, let's go back to the concept of a day.

The day is when it's clear and if it's clear, it's because the sun's rays shine on us.

On the other side of the Earth, at the same time, no ray of Sun (they cannot cross the Earth) and therefore it is night.

At all times, there is half of the planet illuminated and half that remains in shadow.

The Moon revolves around the Earth so sometimes it is opposite the Sun (and is therefore clearly visible to Earthlings immersed in the night), sometimes it is on the same side as the Sun (and is therefore visible to Earthlings in broad daylight).

However, there is one important thing to add: its shape.

Indeed, what we observe is the illuminated part of the Moon.

If the Moon is in the opposite direction to the Sun, the whole part turned towards the Earthlings is well lit: we see a nice disc, it is the full moon.

It's a bit like reading a book: with a lamp over your shoulder, the pages are well lit and reading is easy.

On the other hand, if the Moon is almost in the same direction as the Sun, not only does the Sun blind us but in addition we only have access to the unlit part of the Moon: impossible to see anything ( it is then the new moon)!

For the intermediate directions between these two extremes, we will see just a fraction of a disc, between a thin crescent (just before or after the new moon) and an almost complete disc (just before or after the full moon), passing through the half moons. -moons (first and last quarters, stack between new moon and full moon).

So you can see the Moon during the day (if the sky is clear), but not just any shape at any time.

For example, the last quarter will be visible in the morning, the first quarter in the afternoon…

Our "ASTRONOMY" file

To have the exact times of moonrise and moonset, you can consult the IMCCE website.


To better understand the phases, you can do a little experiment that you will find on page 18 of this book (published by Réjouisciences).

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This analysis was written by Yaël Nazé, astronomer at the Institute of Astrophysics and Geophysics of the University of Liège (Belgium).


The original article was published on

The Conversation website

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