November 23, 2019

For Fibonacci Day, an agave plant

1, 1, 2, 3: It's Fibonacci Day!

Today's date, November 23, can be represented as 11/23, or 1,1,2,3—a Fibonacci sequence of numbers. Likewise, as the leaves on the Queen Victoria agave in today's image spiral out from the centre, they also express the Fibonacci sequence. This unique sequence of numbers was introduced to Europe in 1202 by the Italian mathematician Leonardo of Pisa (posthumously named Fibonacci) in his revolutionary work the 'Liber Abaci.' The book begins by describing the Hindu-Arabic numeral system or 'Modus Indorum’—0 1 2 3 4 5 6 7 8 9—showing how their application could simplify trade and make calculations faster and easier (most of Europe at this time used Roman numerals).

In the third section of his book, Fibonacci goes on to describe various mathematical problems including a thought experiment about increasing rabbit populations, which results in a Fibonacci sequence. The sequence is determined by adding the previous two numbers together to determine the next number: 1, 1, 2, 3, 5, 8, 13, 21, 34, etc. Since then, mathematicians, scientists, and artists have been studying and applying the Fibonacci sequence and the Fibonacci numbers that make it up. While Fibonacci gets the credit for this work, he wasn't the first to discover it. Research published in 1985 posits that ancient Indian mathematicians had been aware of and written about the sequence for more than a century before Fibonacci's work.