One of the things that the conference of 1884
addressed was: "What do we do about time?" So the discussion went something like
this. People use time to plan their lives; it doesn't make sense to have
time changing minute by minute. And if you think about planet Earth, it rotates: 6 hours — 12 hours —
18 hours — 24 hours and if the sun is over here everywhere gets to be noon at some point during
the 24 hours. What the conference said was: Let's block out time. Instead of going
strictly by the sun, minute by minute, let's block out time into blocks of the planet
that are one hour wide. OK? For that width — that distance in real estate — we
won't change the time, we'll freeze it. Then we'll cross a line, jump an hour,
and freeze time for another hour, and so on. How big are those slots?
Well, the Earth has a full 360 degrees, it does this in 24 hours; so what does it go
in one hour? 360 divided by 24 is 15 degrees per hour. So this produced the concept of time zones. Each time zone — the bit within which we freeze
time — don't allow it to change minute by minute with the sun — the width over which we freeze time
is 15 degrees of longitude. Start at Greenwich: number off 7.5 degrees east, 7.5 degrees west,
makes a 15-degree time zone centered on Greenwich. That's start time for the world; then hours going
west, hours going east — a series of time zones. How many time zones will there be,
each one hour wide? — 24 — 24 hours. Here are the time zones of the world. This is not the map in your textbook; this is a
map from another book. Why am I using this map instead? Because your map only shows the time
zones on land; this one shows them in the ocean also, and I need that. In the ocean, the time
zone boundaries simply follow the meridians, every 15 degrees. So you're crossing the
ocean: you cross a line, you change your clock. If we adhere to these straight lines on
land, we would get into a bit of trouble. What if one of these time zones
goes through the middle of a town, and it's eight o'clock on one side of
town and nine o'clock on the other? When do schools open? When do bars
close? When . . . how do you do business? Hey, could get worse than that. What if the
time zone boundary goes through your home, and it's eight o'clock in the kitchen
and nine o'clock in the living room! OK. So on land, time zone boundaries are adjusted.
They become these rather more irregular lines, as they follow political boundaries. Most
countries around the world are small enough that they can more or less fit into one
time zone, with a bit of manipulation, and so that typically is what they do. Here is the prime meridian going through
England. England is of course on that time. The whole of western Europe decided they wanted
to be on one time, and their time is an hour ahead of Greenwich — even though Portugal, in the
southwest corner of Europe, should, by the sun, be an hour behind Greenwich. So
clock time and solar time in Portugal are off by about two hours, which is at
least part of the reason why restaurants in Portugal serve dinner at 9:00 or 10:00 at
night. A big country like the United States spans multiple time zones. What time zone are we
in? — Pacific Time. Going eastwards, you get to Mountain Time, one hour ahead; then Central
Time, one more hour; and then Eastern Time, another hour ahead. Four time zones. There's
a fifth one up here in eastern Canada, and Alaska is behind Pacific Time, and
Hawaii is even further back than that. There are some places where groups of countries
decided they wanted to be together: for example, these . . . this block of African countries
here are all on Greenwich time. This whole block of countries here wanted to be together on the
same time, which is two hours up from Greenwich, and that including this country here, so when you
cross that political boundary there, you actually change your clock two hours. This time zone (the
dark one here) is not used at all in that area. Even within the ocean, there are
one or two time zone anomalies. The Canary Islands — which
we mentioned in Chapter 1 in connection with a possible tsunami —
they are on the same time zone as Spain, the country to which they are politically
connected. And the Galapagos Islands out here in the Pacific are on the same time as Ecuador,
the country which they are politically part of. Then there were countries that did not participate in the 1884 conference, and decided that they
would set time their own way; and you will see some interesting times here: India is five
hours and thirty minutes ahead of Greenwich. Newfoundland — three hours and thirty minutes
behind Greenwich, and possibly the most absurd of all, one of the small countries here on the
north coast of South America — and I honestly don't know which one it was — decided
that they wanted to be within 15 minutes of the correct time by the sun. Their time
is 3 hours and 45 minutes behind Greenwich. Across the bottom of the map
here are a set of numbers. The numbers on this side are plus numbers,
the numbers on that side are minus numbers. If you look at your textbook, you'll
find that these are plus numbers, and those are minus numbers. So how come we
have these two opposite numbering schemes? Well, it's like this: one of them is based on
how many hours you add or subtract to your time to get to Greenwich, and the other is based on
the number of hours you add or subtract from Greenwich time to get to your
time. That's confusing, isn't it? I suggest you forget all
about those numbering systems. Living in the United States, a big country
with several time zones, you guys have a better understanding of time zones than most people. So
you should all be able to answer the question: "What time is it in New York right now?" Very
practical question. If you have friends or you want to do business, when do you pick up the
phone and call? When, more important, do you not pick up the phone and call? — Well obviously
that depends on the time that you're viewing this video, but hopefully you chose a time
three hours ahead of where we are now. If you're watching this in the middle of the
day — say 12 noon — it's 3 pm in New York. If you're watching it at 9:00 at night, it's midnight
in New York. You are aware of these time zones, so you know that if you go eastwards, you move
the clock forwards, and coming westwards you set it back. And that's the way to
remember these time zones — forget the numbers at the bottom. Now, the next question this Chapter addresses
is: "How do you determine where you are?" OK? You're on a ship out in the ocean.
There's no land in sight in any direction. How do you figure out where you're at?
Well that means: how do you determine your latitude and your longitude? — because
then you can place yourself on the chart. Well latitude is easy: you use the sun. The sun is
93 million miles away, so the sun's rays come in parallel — exactly the same direction everywhere. If you're in a boat on the equator, the sun's
rays are coming in directly overhead, aren't they? If you could take your boat to
the north pole (which you can't), the sun's rays would be coming in
horizontally. Somewhere in between, the sun's rays come in at an angle. So look:
90 degrees between the sun and the horizon . . . some smaller angle . . . essentially zero degrees . . .
the angle between the horizon and the sun tells you your latitude. Can you take
that measurement at any time of day? No. Anywhere, at dawn, the sun is zero degrees above
the horizon. It gets higher, higher, higher. When is it at its highest point? — 12 noon. So this observation
is called "taking the noon sight." There's a picture in your book of a person using an instrument to
do just that. This instrument is called a sextant — the modern descendant of an ancient,
ancient, instrument used for many centuries, called an astrolabe. This is the modern one. And you look through it: you're looking . . . at the
horizon, and there's a separate field of view that shows the sun, and a mirror system that allows you
to bring the sun down, until the sun matches the horizon. So you crank the wheel, and bring the sun
down until the sun's on the horizon, then you read off the angle that you've cranked the sun down, and
that's your measurement. So what you do: when it's getting late morning, you
start making measurements of the sun. And each time you make another measurement,
you have to increase the angle a little bit, because the sun is getting higher. When you stop
increasing the angle, it's noon. You have the time: is noon — local time — by solar noon, and have the
angle that you're going to use to determine your latitude. Sailors have done this
successfully for thousands of years. Now what about longitude? That's more difficult. There is no relationship between the sun and longitude. Noon by the sun goes all around the planet every 24 hours. So for centuries, until very recently, sailors could
determine their latitude, but not their longitude, and many of the maritime disasters of history
result from not knowing exactly where you are — not knowing your longitude. So how can you sail
the ocean at all, if you don't know where you are? Well, you know half of it: you know your latitude,
but not your longitude. Well, it's not perfect, but you can do pretty well through a process called
"dead reckoning". You can tell how fast your ship is going. An experienced sea captain would say
he could just look at the water and he knew how many miles an hour the ship was going.
He's probably right — with experience. But there are actual quantitative ways. You know how many feet
long your ship is; you drop something overboard at the front end of the ship; you time how long
it takes to get to the back end of the ship, as you sail past it; and the distance
divided by the time is your speed. Simple. OK? So you've got a chart.
You have set off from this port city, and you know that you sailed eastwards for
three hours at 10 miles an hour, then you changed course and sailed north-eastwards for the
next 15 hours at 8 miles an hour. OK? And so on. Now you reckon you're at this point here. Where's this information recorded? — ship's log. That's why the ship's log is such
an important part of survival. That ship's log has even carried through into
modern movies: "Star Trek — captain's log — star-date . . . " The ship's log recorded — hour by
hour — exactly what was going on: direction, speed, weather conditions, any
evidence of ocean currents, stuff like that. Never missed a record — their
survival could depend on it. Let's say that now we get a noon sight, and
we discover that we're actually somewhere on this line of latitude here. What would
they do? They'd take this whole line and swing it around to make that point move to
this point, and say: OK, then we must be here." So yeah, you can do a reasonable job
of getting along without longitude, but by no means perfect, and lots
of ocean disasters as a result.