The Eiffel Tower is taller in summer (it also shrinks in the winter). The reason? Thermal expansion (and contraction).
How is the Eiffel Tower taller in summer?
At 330 meters high, you won’t be able to tell just by looking at it that the Eiffel Tower grows by 15 centimeters in the summer. At 132 years old, the Tower spent 42 glorious years as the world’s tallest building. And the structure wasn’t even meant to be permanent.
The Eiffel tower is made of iron, puddled iron (or wrought iron) to be exact. And to be even more precise, it’s puddled iron from the Forges de Pompey near Nancy, France.
At the time, architect Gustave Eiffel had relied heavily on iron and had not worked with steel in any significant way in his architecture. Of course, steel does not change during temperature fluctuations, whereas iron does.
The growing and shrinking Tower
According to the structure’s tourism website (cited below):
“When temperatures rise, the Tower increases in size! This is a natural physical phenomenon called thermal expansion. Heat causes an increase in volume that makes the Eiffel Tower a few centimeters taller. This expansion also causes the Tower to tilt slightly away from the sun. The sun only hits one of the 4 sides of the Tower creating an imbalance with the other 3 sides, that remain stable, thus causing the Eiffel Tower to lean. In this way, the sun’s movement over the course of a clear day can cause the top of the Tower to move in a more or less circular curve measuring approximately 15 centimeters in diameter.”
You probably can’t see it in your photos, but you read that right – the Tower does lean slightly in the summer since the sun only hits one side directly, causing it to expand.
This expansion goes away when the sun isn’t strong.
Thermal contraction is a winter problem. During the cold months, the metal structure shrinks from its normal height.
You might think all this contracting and shrinking causes the iron to become weaker, but the Tower is so large that there’s no risk of cracking. It was also built to withstand wind. In fact, it was designed to sway with the wind (or at least vibrate) to avoid structural damage. — WTF fun facts