PhiDay.org exists to increase awareness and interest in Phi, one of the most interesting numbers in mathematics. Phi, is the Greek letter used to designate the set of numbers 1.618… and it’s reciprocal 0.618…, hence the designation of June 18, or 6/18, as its day of recognition.

Phi is found throughout nature and yields efficiency as well as beauty in design. It is also known as the Golden Ratio, Golden Mean, Golden Number or Golden Section. Euclid of ancient Greece wrote of it and Leonardo Da Vinci used it in his compositions, referring to it as it was known in his age as “The Divine Proportion.” Since the dawn of civilization, this intriguing number has captured the minds and hearts of artists, craftsmen, designers, architects, writers, poets and many others. It may inspire you as well.

Phi is found in mathematics with unique mathematical characteristics of this number that make its square one greater than itself and it’s reciprocal one less than itself. No other number has this property. It is found in Geometry in basic constructions using bisected line or an equilateral triangle, square or pentagon inside a circle. In the solar system, Phi is found in the relative dimensions of the Earth to the Moon and Saturn to its rings. In life it is found in the dimensions of DNA, the proportions of many animals and most notably in the human form, where it defines our perceptions of beauty. Its uniqueness and beauty have not been lost upon the observant eye of humans, and has been used by mankind to achieve a harmony with nature and beauty in design in great architecture, masterpiece paintings, award-winning products and even familiar logos of products that you see and use every day. That’s a rather amazing role for a single number to play in all that we experience in the world around us, and that’s just the beginning.

So Happy Phi Day to you. Enjoy the wonder of knowing that you’re connected to something much larger than you might ever have imagined.

Great phi website

Well my teacher is having a phi day celebration so we missed math class today so Yaaaaaaaaaayyyyyyyyyy!!!!!!!!!!

I enjoyed trying to understand theconcept of Fibonachi sequence. I studied

math many years ago. I enjoyed the mental stimulation Thank you once

again. I hope that I will have the opportunity to again be exposed to more

mathematics!

Man, I can’t believe I didn’t even think of it the other day. I guess I’m more about Jan. 8, 2016 (16-1-8) to most of the world. Or even, Jan. 6, 2018 (1-6-18) US. Has anyone done the math on the 618th day of the 21st Century, or the 6,180th? I turned 21,618 days old at the end of the first quarter (day 90-longevity) . Never thought I’d make it this long. Or is it ‘this far’? ;^ )

Yeah! My children are happy!

phi day is the 139th day in a year

Phi day is the 225th day in a year

I recently had a conversation with my middle-school son about Pi Day (this year, Super Pi Day, 3/14/15), and I commented that there are other mathematical constants that also merit their own day. Until I came across this website, I did not know that someone had set up a Phi (φ) Day, so this is great. Thank you. I would observe φ Day on 1/6 rather than 6/18 (1/φ Day) simply because 6/18 is typically after the school year. Why miss an opportunity?! In 2018, there will be a Super φ Day, 1/6/18.

Another constant that deserves its own day is e (base of natural logarithms). e Day would be 2/7, and also in 2018, there would be a Super e Day, 2/7/18. (I did not find a similar e day website, but maybe I missed it.)

Thus, three months running at the beginning of each year, there could be φ Day in January, e Day in February, and π Day in March. Why not? 2018 will be a Super year for two of them, as 2015 is for one of them.

Lastly, there should also be an i (√-1) Day, but siting this one is a bit trickier. Perhaps, it should be celebrated on February 29 for the simple reason that it is “imaginary” for 3 out of 4 years (ignoring century-year issues). i is also related to π, which has its own day, and e, which should have its own day. By that relationship, e^(iπ) = -1, i^i = e^(-π/2) = 0.207879…. Dividing i^i by 3 (as in 3 out of 4 years) gives 0.06929… = 2.0095…/29 ≈ 2/29. This should verify 2/29 as i Day, and, next year, 2016, is the next chance. It should be done.

Thank you very much for your consideration.

Great thoughts, David. Anything we can do to help our students have a better appreciation and understanding of mathematics is a great idea, and some of your ideas are quite novel.