Why the Eiffel Tower Leans Away From the Sun

Picture the Eiffel Tower on a clear Paris morning. It looks motionless. Yet sunlight is quietly changing its shape.

The side facing the sun warms and expands more than the shaded side. The difference makes the tower lean slightly away from the light. As the sun moves across the sky, the direction of that lean changes too.

According to the tower's operator, the top can trace a roughly circular curve about 15 centimeters across during a clear day. That number describes its movement, not a measurement of how much taller it becomes.

A building that moves without walking

Thermal expansion sounds like a textbook phrase. Here, it becomes a story you can picture: an enormous iron landmark responding to sunlight, then cooling as night arrives.

The movement is far too small for visitors to notice. The operator says these natural changes do not affect the structure's strength.

The seasonal height question needs more care. The tower's own explanation describes a small gain in height, while a university-authored article in The Conversation gives a larger seasonal estimate. Those sources disagree on the amount. They agree on the mechanism behind the lean: uneven heating makes one side expand more than the other.

That is the most useful distinction to remember. A tower can get taller as it warms, and it can lean when one side warms more than another. Height change and sideways movement are different measurements.

Watch the story

Our short film tells the story of the tower's daily lean: https://youtu.be/A7ywwYIBoso

More short stories from Aha Lantern: https://www.youtube.com/@AhaLantern

Sources and a note on the film

The film follows the tower operator's explanation of the 15-centimeter movement. Its closing line, "the tower doesn't grow in summer," is too broad: heating can increase the tower's height as well. The distinction is between height and sideways motion, not growth versus no growth.



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