自然、艺术和数学 | 向日葵 Sunflower (© Dileep Chandran/Alamy)-立刻壁应

斐波那契日

向日葵原产于美洲，是一种引人注目的开花植物。一年中，无论什么时候，它都向着天空生长，愉快地歌颂着夏日。事实上，它的花头由许多极小的花朵组成，而这些花朵最终会成熟、变成种子。但是你知道吗？向日葵上也蕴含着大自然的数学奇迹。

照片中这朵向日葵的种子分成两组螺旋排列，一组顺时针方向盘绕，另一组逆时针方向盘绕，彼此镶嵌。如果你将任意一组螺旋线绘制在图表上，你会发现它十分接近斐波纳契数列（1，1，2，3，5，8，13，21…）。在斐波纳契数列中，每一个数字都等于前两个数字之和。虽然这个著名的螺旋公式被认为是13世纪意大利数学奇才斐波那契的作品，但其实印度学者对这个数列的描述比斐波那契早了好几个世纪，而他们或许也并不是第一批发现这个数列的人。但无论这个数列是如何被发现的，每年的11月23日都被认定是斐波那契日，1，1，2，3，你发现其中的奥秘了吗？

Nature, art, and…math?. Fibonacci Day

The sunflower is an eye-catcher, growing to the sky and brightly singing of summer no matter the time of year. Helianthus annuus is native to the Americas, and its flowering head is actually made up of more tiny flowers that mature into seeds (and, of course, get eaten around the world). But did you know that sunflowers also bring one of nature’s mathematical wonders to life?

The gorgeous sunflower displays its seeds in two seed spirals that twist and curve in opposite directions, fanning out from the centre to the golden petals. If you mapped either of those spirals on a graph, they would closely follow the Fibonacci sequence (1, 1, 2, 3, 5, 8, 13, 21…), where you add a number to the one before it to get the next number. While the famous spiral formula is attributed to Fibonacci, the 13th-century Italian math whiz, scholars in India described the sequence centuries before him—and they probably weren’t the first to figure it out either. But regardless of the origin story, each November 23 (11/23…get it?) we celebrate the infinite series known as the Fibonacci sequence.