You know, February 29, that day that only comes
along every four or so years? It was the Egyptians who first realized the need to add a day every four years to keep
their calendars in sync with the solar year, and it was the Romans who first designated the 29th of February as that extra day.
(Brunner) But why is a Leap Day necessary at all? Why can’t we just come up with a calendar that works without
all this mucking about? In order to understand the concept of a Leap Day, we probably should start with the entire concept
of Time. It’s a bit more complex than just “daylight
come and me wanna go home.” (Belafonte)
It probably should come as no surprise that isolated societies living in temperate zones, in particular, hunters
and gathers, have no real concept of numbers. Not really. There is an Amazonian tribe, for instance, that only
has terms for “some” and “more,” but really nothing else. (Highfield) But then, why do
you need to count if all you have to do is get up whenever, have a leisurely breakfast of whatever fell off the trees during
the night, maybe do a little hunting in the afternoon, snack a bit, maybe take a nap, maybe cook up whatever you got in the
afternoon, and then sit around the fire telling jokes until you shuffle off to bed? And it never changes. But
along came civilization, and with civilization came agriculture, and agriculture meant, at least to a degree, that you kinda
needed to know how to count, and that involves numbers.
You see, the whole problem with relying on agriculture to survive is that you need to know fairly precisely when
to plant your crops, especially the further north you live. In fact, it would probably be a good idea to get plants
into the ground as soon as possible in the spring, and harvest them as late as you can in the fall. And to do that,
you’re going to need a Calendar.
Really, calendars are very easy things to make, especially if you don’t get too wigged out on specific months
and years. And you can make your own! Simply get somebody to go out with you to an open field that faces east,
more or less, every day for a year at sunrise. You stand at a set point at the westward end of the field and have your
buddy stand in the east. When the sun rises, have her whack a stick into the ground where you first see the sun rise
over the horizon. Even though it may seem like yesterday’s stake is pretty much where today’s stake should
go, over time you will notice that those stakes are moving – everyday the sun rises at a slightly different spot on
the eastern horizon than the day before. And over time you will notice that the stakes only go so far left before they
stop and then head right, where they will eventually stop and then head back left. When you get back to where you started,
that’s a year. The farest stake to the left is the first day of Winter – the Winter Solstice – and
the farest stake to the right is the Summer Solstice. And in the middle… those are the Equinoxes – both
Spring and Fall. Ever see the movie Cast Away? Remember the elliptical thing the character played by
Tom Hanks drew on the cave wall? Yup. A calendar. And, though a bit more advanced, it’s Stone Henge.
Really, what you are doing is tracking the earth’s
orbit around the sun. And, really, for all practical purposes, that calendar is all you need. It tells you when
to plant and when to party.
though, is when you try to assign specific days that you expect to stay the same, because they won’t. You see,
the earth is going around a star that itself is orbiting the center of the galaxy, and that galaxy is also orbiting the center
of the universe, and then just to muck things up even more, the entire universe is spinning and expanding at the
same time. Basing our position in the universe relative to other stars and planets is a bit like basing your position
on the Kansas turnpike by the cars and trucks you pass and that pass you. It’s a bit imprecise, to say the least.
But imprecision is something that bothers us. We try to make it work out right. And therein the problem lies.
Remember when Mrs. Bimbaum explained leap years in
the third grade? She told you that years really weren’t 365 days long, but that they were actually 365 and
one quarter days long. Therefore, every four years, you needed to add an extra day to make everything work out.
Of course, at the time you believed it, because Mrs. Bimbaum knew everything, but didn’t the idea of a quarter day seem
just a bit… odd, even then? I mean, when, exactly, is that quarter day? There isn’t,
after all, an extra six hours at the end of every year that we seemingly don’t know what to do with.
The answer is that it’s not really the year
that comes up long, but the days that come up short. On an average, it takes the earth 23 hours, 56 minutes, and 4 seconds
to make one complete rotation – how long it takes for “two successive returns of the Sun to the local meridian.”
And then, notice the word average. Not all days are the same length, depending on where the earth’s at
in its orbit and what latitude you might be at. (Coffee)
And then there’s another problem. Days are actually getting longer. And, no, I’m
not talking about the amount of daylight that varies depending on the season and your latitude. The moon, slowly, is
getting further from the earth – about one and a half inches a year, or roughly the speed at which fingernails grow.
This has the effect much the same as an ice skater spinning in circles. To slow down, she simply extends her arms.
The further the moon is from the earth, the slower the earth rotates, and the longer the days are. In a few billion
years, this could really have a noticeable effect on life on the planet, but for now we’re OK. (Why the Moon…)
So, really, if every day had one hour that was just
a bit shorter than the rest, or if all of our hours weren’t quite sixty minutes, or if every minute weren’t quite
sixty seconds, or if every second weren’t quite a second, everything would work out almost fine, once again depending
on where you live. But since we don’t do that, then the years come out to be that one quarter of a day longer
that Mrs. Bimbaum told you about.
thing, Mrs. Bimbaum wasn’t quite right. A year, relative to our orbital position in that moving field
of background stars – how long it takes us to get back to the exact place we started from after a complete orbit, is
365.2425 days… or perhaps 365.2424 days (or 365 days, 5 hours, 49 min, and 12 seconds, give
or take). (Loy)
The thing is, if
you don’t account for that extra quarter of a day somewhere, somehow, then eventually everything is going to get all
out of whack, technically speaking. Eventually, you’d look at the calendar and say, “Hey! It’s
Spring!” But it won’t be. And then you’re going to be in real trouble when your entire seed
crop is killed by one of those late winter freezes.
Even adding in an extra day every four years isn’t quite going to do it. That’s why we have leap
centuries. Any century year that is not divisible by four hundred does not have a leap year. So we had a leap
year in 2000, but we won’t in 2100, nor will we in 2200 or 2300, and the last time we had a century year that had an
extra day before 2000 was in 1600. Kinda makes you wish you’d paid more attention to the leap year in 2000.
But even that is not completely accurate. That’s why we will eventually need a leap millennia, but it won’t
be any time soon. In about 3,300 years our calendars will be off by a day. (Brunner)
On the other end of the scale, we already have leap seconds. And, no, I am not making
this stuff up. 1982 was the first time I realized we had a leap second, and I haven’t thought about time the same
since. Come to find out, we have them all the time, the first coming in 1972, and the most recent on June 30, 2015.
You see, humans can make
clocks really well, but clocks are not the same as a calendar. A clock can be made with anything that happens at a steady
rate. Ever see the water clock outside of Silver Dollar City? You really can measure time, albeit crudely, with
dripping water. Spring-loaded cogs work better. Zapping a quartz crystal so it vibrates works even better, just
as long as you know how many times it vibrates in a second. And if you want to be really accurate, then you need an
atomic clock, where slightly heated cesium atoms, when microwaved (more or less), change their energy state, and then these changed
atoms are sorted from the rest and used to make a crystal oscillate at exactly 9,192,631,770 times per second. That’s
a lot of work to know what time South Park comes on. (Dwyer)
And if that’s not confusing enough, on a quantum level, there is absolutely no reason
at all why what we call time – the occurrence of one event relative to others – happens in a linear order.
In other words, there really is no reason whatsoever why what we call time progresses from yesterday to tomorrow, and not
the other way around, or in any order at all, as far as that goes. And then there’s Einsteinian Relativity, which
means (among other things) that identical clocks will run differently if one is moving faster than the other. In other
words, the clock in your car actually ticks faster when you’re moving than it does when you’re parked.
But here’s the thing: Even if clocks all
behaved the same, just what are you using them to measure? We can know without a doubt that there are sixty seconds
in a minute, and sixty minutes in an hour. After all, we made those units of measurement up. They did not exist
before we – humans – decided that they did. Somehow we know what a standard second is, just like somewhere
there is an ounce that all standard weight is derived from. Consider this: If there were some kind of apocalypse,
say a meteor or nuclear war or zombies, and you had to come up with time all over again… from scratch… how would
you do it? But I digress. We did do it, and in the event of the Zombie Apocalypse, you probably have better things to worry about than what time it is.
So we have these units of measurement called seconds
and minutes and hours, and they work just fine as long as we are only measuring seconds and minutes and hours. But when
you try to use them to measure something that we didn’t make up, something as complicated as, say, how long it takes
for the earth to rotate once on its axis, what is commonly known as a day, then you can get really confused, especially
if you want everything to come out even when you’re through. That’s when we have to start adding in leap
seconds, and leap days, and leap years.
advice: Ignore it. Be content to know that there are people who get paid to come up with clever ways to determine
just how late you are to work in the morning or When the Earth is Supposed to End or when South Park comes on. After all, if a day is really
only 23 hours, 56 minutes, and 4 seconds … who cares? Tomorrow will come just the same… or not.
And if the mantle clock seems to be off a few minutes every now and again, then just change it… or not. After
all, it’s probably close enough.