Feeling Grumpy about Pi Day - Numberphile

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Yeah. No, I'm a grumpy old man. I'm allowed to be. I'm I'm grumpy. I'm old. So So you're here filming today for Pi Day and you're you're worried because you know you've only got a day to do the editing in. Uh I want I wish to make the case that Pi Day is not actually the 14th of March. Pi Day is the 22nd of July. So you got plenty of time. Pi Day. Yes. Is is uh March 14th 3:14, right? So 314 3.14 Pi. But it's only Pi Day if you put your month at the beginning and then your day. And sensible people put the day first then the month. So tomorrow is the 14th of March, not March 14th. And 14.3 is not pi. So the reason why 22nd of July is pi day is because 22nd of July is written 227 or 22 over7 and 22 over7 is a pretty good approximation to pi. >> But not exact. It's like is it is it the best approximation among the months and days we've got? >> Absolutely. Yeah. I know it's it's a pretty good approximation to buy and it's certainly at least as good as 3.14 or or the March 14th >> that assumes putting the 22 before the sevens. Aren't you aren't you guilty of the same kind of parochialism? Some people call it 722. >> They do but yes you want to talk about parochialism most of the world talks about 227 not 722. And I think there are actually quite good reason you know. So okay there are various ways you could choose to write a date right you could start you could write it the way that I just did of 22nd of July 2026 day month year that's called the little Indian approach because you start with the little bit and work towards the big bit you could write it the other way round you could write 20 2026 July 22nd that's the big Indian approach because you start with the the big bit the year and then work your way towards the little bit >> and you call that big Indian even though it's at the start not the Yes, I've never quite understood that. But anyway, nonetheless, little Indian is starting with the starting with the day. Big Indian starting with the the year. There's good reasons to do either of them, right? The reason you might want to start with the year is if you write your date that way round, if you've got a whole bunch of strings with that date in it and you just sort them, then they'll actually come out in date order, which is quite a handy thing if you actually want to sort a bunch of dates. The little Indian approach is quite useful in the sense that if somebody asks you what's the date, they probably know what year it is. It's quite likely they know what month it is. What they're really asking you is what day is it? And therefore, you start with the most important piece of information, what the day is, right? That's reason for a little Indian. >> The most granular sort of uh >> yeah, it's the probably the information that you're most likely to need, right? What day of the week? What day of the month is it? What rather than what month is it or what year is it? So, you start with the important stuff. The approach that gives you pi day being March the 14th is called middle Indian because you start with the middle bit and there is no justification for that at all that I can think of. It's just a way of writing the date and it's kind of arbitrary. I think the US is the only country in the world that does it. >> What do you call the terrorist attacks that happen in New York in 2001? >> Uh what do Americans call the 4th of July? >> Good answer. They don't call it July the 4th, do they? >> So once in a while they slip and accidentally use a sensible way of writing dates back there. Anyway, look, I should hasten to point out I don't take this at all seriously. You know, I don't wish to offend anybody. I really don't care how you choose to write your date. It just amuses me um that it's such a thing. >> You're an astronomy professor. You're a retired astronomer. what Indian does to scientists prefer in their like cataloges and data and you know observations and if I'm looking at a picture that was taken by the Hubble Space Telescope and it's dated what's going to be on there >> so generally if you're going to write out down a date you write it big Indian just because you want to be able to sort things very easily so you do it that way >> start with the year >> start with the year but actually astronomers use a thing called Julian date which is just basically counting days it's just a number and every day the Julian date goes up by one so every day has a number. And so actually that's the the most useful way in astronomy for counting dates because actually what you want to know in astronomy is well how long ago did something happen? We just need to subtract that Julian date from today's Julian date and that will tell you how long ago it happened. If you want to know the time between two things, you just take the difference between the Julian dates. >> Do you know what Julian dates we need to look up? 31 314 3,141. All the pi julian dates. >> We need a very Yeah, we and we're up to very big ones now. So actually we'll get lots of decimal places but it might be you might have a long time to wait for it. >> Okay. >> And we are and again we also are being uh base 10 centric. >> Absolutely. Yes. Very so. >> Pi was historically rarely calculated this way because it's notoriously inaccurate to try and get I know we're idiots. Uh it's notoriously inaccurate to try and calculate pi uh by measuring a circle.