Latitude, Longitude and Time Zones

A globe lets you hold a model of Earth in your hands. Its lines help you find places, even far across an ocean.

A ball with two poles

Earth is almost a sphere, a ball shape. A globe keeps the continents and oceans in their proper shapes and sizes compared with each other. A flat map stretches or squashes some parts. You cannot flatten a ball's surface without changing it.

Earth spins around its axis, an imaginary line through its center. The axis reaches the surface at the North Pole and South Pole. Many globes have a rod through these points so you can turn them.

Two kinds of lines

The equator circles Earth's middle, halfway between the poles. It runs east and west. Its length is about 40,075 km (24,901 miles). It crosses Ecuador, Brazil, Kenya, and Indonesia.

Other east–west circles are parallels, or lines of latitude. They never meet. Imagine rings around a ball, getting smaller toward either end. Equal changes in latitude have almost equal spacing on the ground. At each pole, the circle shrinks to a point.

Meridians, or lines of longitude, run from pole to pole. Each is half a circle. Picture the lines between orange segments: wide apart around the middle, together at the ends. All meridians have the same length. The prime meridian is their starting line, through Greenwich in London. A metal strip there marks the historic line chosen by mapmakers.

An address made from lines

Together, parallels and meridians form a grid. Find one line of each kind and follow them to their crossing. That crossing fixes a position on the globe. You will soon give each line a number.

Compare two descriptions of a meeting place:

• "Beside the bridge" gives a relative location. It compares the place with another feature.
• A latitude and longitude pair gives an absolute location. It identifies a position in the world grid.

The lines are imaginary. You do not need to see a stripe on the ground to cross the equator! When you trace a globe, follow the equator around its middle. A line running from top to bottom is a meridian.

You can describe a place using two halves of Earth. Start with the equator, then check the prime meridian.

North or south?

A hemisphere is half a sphere. The equator separates the Northern Hemisphere from the Southern Hemisphere. A place north of the equator is northern. A place south of it is southern. A point exactly on the equator sits on their boundary.

East or west?

The prime meridian and the opposite meridian, at 180°, make a full circle. Together, they divide Earth into Eastern and Western Hemispheres. From 0°, go east up to 180° for the Eastern Hemisphere. Go west up to 180° for the Western Hemisphere.

A place away from these boundary lines belongs to one north–south half and one east–west half. Egypt is northern and eastern. Australia is southern and eastern. Argentina is southern and western.

Read the map's labels

On many world maps, north is up and Greenwich is near the middle. East then appears on the right. A Pacific-centered map puts Greenwich near an edge instead. Follow the numbered lines and direction letters. Page position alone cannot tell you a hemisphere.

Imagine a place south of the equator and west of Greenwich. First name the Southern Hemisphere. Then name the Western Hemisphere. You have used two different dividing circles, so both names describe the same place.

Countries can cross a boundary

Brazil, Kenya, and Indonesia have land on both sides of the equator. The prime meridian crosses the United Kingdom, France, Spain, Algeria, Mali, Burkina Faso, Togo, and Ghana. Each has land in both eastern and western halves. Kiribati's Pacific islands reach into all four hemispheres.

The Western Hemisphere includes parts of Europe and Africa, too. Portugal, Ireland, and Senegal lie west of Greenwich. It is not just another name for the Americas.

Most land and most people are in the Northern Hemisphere. Much of the Southern Hemisphere is ocean. Find your own town on a globe. The 48 connected U.S. states lie in the Northern and Western Hemispheres. In the United Kingdom, check which side of Greenwich your town lies on.

Latitude gives you a north–south position. Its number measures distance from the equator as an angle.

Start at zero

The equator is 0° latitude. The symbol ° means degrees. Imagine two lines starting at Earth's center. One points to the equator; the other points to your place. The angle between them gives its latitude. A right angle takes you to a pole.

The North Pole is 90°N. The South Pole is 90°S. Latitude never goes beyond 90°. Write N or S after a nonzero latitude: New York City is near 41°N, while Wellington is near 41°S. The equator needs no letter.

The lines run east–west, but their numbers measure north or south. Think of climbing a ladder: the rungs run across, but you move up or down between them.

Compare distance from the equator

A larger latitude number means farther from the equator. Cairo, at about 30°N, is closer than Sydney, at about 34°S. Compare 30 with 34. The letters tell the side, not how far away it is.

Farther south means a larger S number. A place at 30°S is south of 20°S. Moving from 30°S toward 20°S takes you toward the equator, which is northward.

Find a north–south gap

For places on the same side of the equator, subtract their numbers. Chicago at 42°N and Mexico City at 19°N have a latitude gap of:

For places on opposite sides, add. Cairo at 30°N and Cape Town at 34°S are:

Trace the path through 0° to see why both parts count.

Turn degrees into an estimate

One degree of latitude is about 111 km (69 miles). Cairo's north–south distance from the equator is about:

The 64° gap gives about 7,104 km from north to south. This measures their latitude separation, not a flight route between the cities. Longitude can separate places east–west as well.

Lines can help describe borders, too. Much of the U.S.–Canada border from Minnesota west to the Pacific follows 49°N. On a map, that part looks straight because it follows one parallel.

Longitude gives you an east–west position. Its starting line is the prime meridian, at 0°.

Measure from Greenwich

A longitude needs E for east or W for west. Numbers rise from 0° to 180° in either direction. The 180° meridian is the same line whether you reach it eastward or westward. It is opposite Greenwich, mostly in the Pacific Ocean, and crosses Fiji's islands.

Unlike the equator, longitude has no natural starting line. People chose Greenwich. In 1884, delegates from 25 countries met in Washington, D.C. They voted 22 for Greenwich, one against, with two not voting. Many ships already used charts based on Greenwich.

Watch meridians come together

Every meridian is a half circle from pole to pole. They meet at both poles. At the equator, one degree of longitude spans about 111 km (69 miles). Near 60°N, it spans only about 56 km (35 miles). At the poles, the meridians meet at one point.

So you cannot use 111 km for every longitude gap. The same number of degrees covers a smaller east–west distance near a pole.

Compare two longitudes

For places on the same side of Greenwich, subtract. Los Angeles is near 118°W and New York City near 74°W:

For places on opposite sides, first add the numbers. New York at 74°W and Cairo at 31°E give:

This gap goes through Greenwich. Sometimes the shorter way crosses 180° instead. Wellington near 175°E and Samoa near 172°W give:

A full circle has 360°, so the shorter gap is:

They are close across the Pacific, despite having large numbers and different letters.

Keep the letter

"31°" alone could mean east or west. Those positions are on different sides of Earth. Write 31°E or 31°W so someone can find the right meridian. Remember the different limits: latitude reaches 90°, longitude reaches 180°. The two longitude directions together make the full 360° turn.

A latitude and longitude pair is a place's coordinates. Read them in order: latitude first, longitude second.

Follow two lines to a crossing

Cairo is at about 30°N, 31°E. Start at the equator and find 30°N. Then find the meridian 31° east of Greenwich. Their crossing gives Cairo's position.

For Sydney, use 34°S, 151°E. First go south of the equator to 34°S. Then find 151°E. Follow both lines to where they meet. You should end up in Australia, in the Southern and Eastern Hemispheres.

Read a place between printed lines

Maps cannot print every possible line. Many show lines every 10° or 15°. You can still estimate a position.

Suppose a dot is halfway between 30°N and 40°N. The interval is 10°, and half is 5°. Its latitude is about 35°N. If it is halfway between 20°E and 30°E, its longitude is about 25°E. Write 35°N, 25°E.

On a usual north-up map, latitude labels appear along the sides. Longitude labels appear at the top and bottom. Trace the grid line from its label to the dot. Check the map's own layout before reading the edges.

Tokyo lies a little more than halfway from 30°N to 40°N. It is just west of 140°E. Rounded to whole degrees, its coordinates are about 36°N, 140°E.

Smaller parts of a degree

An atlas may show minutes, marked with ′. A degree contains 60 minutes. Thirty minutes is half a degree. So London's latitude, about 51°30′N, is also 51.5°N. These minutes divide an angle; they do not measure a trip's time.

Map apps often use decimals with signs instead of letters. In "40.71, -74.01", the first number is latitude: positive means north. The negative longitude means west. That pair locates New York City. In "-33.87, 151.21", the negative first number means south, and the positive second means east: Sydney.

At 0°, 0°, both starting lines meet. This point lies in the Atlantic Ocean's Gulf of Guinea, south of Ghana. A zero needs no direction letter. Before finishing any coordinate pair, check its order and letters against the hemispheres you expect.

Coordinates help you compare places and describe patterns. You can say more than just a place's two numbers.

Which place is farther north or west?

Reykjavik is near 64°N, 22°W. Anchorage is near 61°N, 150°W. Both are north of the equator, so 64°N is farther north. Reykjavik wins that comparison.

Both are west of Greenwich. A larger W number lies farther west from Greenwich, so Anchorage is farther west. Read the correct part of each pair: longitude cannot tell you which place is farther north.

Across Greenwich, keep both sides in your thinking. Places at 10°E and 10°W lie 20° apart through 0°. Their equal numbers do not put them on the same meridian.

Describe a place in words

Nairobi is near 1°S, 37°E. Its small S number tells you it is just south of the equator. Its E tells you it is east of Greenwich. You can write: "Nairobi lies in East Africa, just south of the equator, in the Southern and Eastern Hemispheres."

A clear description can combine coordinates, hemispheres, and a nearby continent, ocean, or feature. Each adds a different piece of information.

Measure how far a country stretches

A country's extreme points are its farthest points in each direction. For the 48 connected U.S. states, the northern extreme is near 49½°N in Minnesota. The southern extreme is near 24½°N by Key West. Their latitude span is about:

The eastern extreme, West Quoddy Head in Maine, is near 67°W. The western extreme, Cape Alava in Washington, is near 125°W. The longitude span is about 58°. Both are W, so subtract their numbers.

Spot a pattern

Rome, Chicago, and Boston all lie near 42°N. They share a latitude, yet sit far apart. Washington, D.C., and Lima are both near 77°W, along the same meridian. A shared latitude does not mean shared longitude.

Look up your town in an atlas or map app. Round its coordinates to whole degrees. Then name its hemispheres. Denver is near 40°N, 105°W; Beijing is near 40°N, 116°E. They are about equally far north, on different sides of Greenwich.

Five named parallels help you find your place on Earth. They form a north–south pattern with the equator in the middle.

Learn the order

Read from the North Pole toward the South Pole:

The two tropics are equally far from the equator. The two polar circles are another matching pair. Each polar circle lies about 23½° from its pole, since a pole is at 90°.

"Can" comes before "Cap" in the alphabet. Reading north to south, Cancer comes before Capricorn. Both tropics are much nearer the equator than the polar circles are.

Follow the lines across land

The Tropic of Cancer crosses Mexico, the Sahara, Saudi Arabia, India, and southern China. Havana in Cuba, near 23°N, lies just south of it.

The Tropic of Capricorn crosses Chile, Argentina, Paraguay, Brazil, Namibia, Botswana, South Africa, Madagascar, and Australia. Rio de Janeiro, near 23°S, lies just north of it. A latitude of 23°S is closer to the equator than 23½°S.

The Arctic Circle crosses Alaska, Canada, Greenland, Norway, Sweden, Finland, Russia, and a small island of Iceland. The Antarctic Circle crosses Antarctica and the Southern Ocean. Its matching name helps: Arctic is north; Antarctic is south.

Read an atlas value

An atlas may print 23°26′ for a tropic or 66°34′ for a polar circle. You may also see 23.4° and 66.6°. These are more detailed ways of giving their positions. The lines shift very slowly over many years. Use about 23½° and about 66½° to find them on a world map.

The named parallels mark important differences in sunlight. They also help you sort places into broad temperature zones.

Where can the Sun be overhead?

Between the tropics, including their boundary lines, the Sun can be directly overhead. At least once each year, it is straight above a place at solar noon. A standing person's shadow then falls right under their feet. Beyond either tropic, the Sun is never directly overhead.

High in the sky is not the same as directly overhead. The word "directly" means straight above you, not off to one side.

Where can daylight last all day?

Inside the polar circles, there are summer days when the Sun never sets. This is the midnight sun. Farther toward a pole, winter brings days when the Sun never rises: polar night. At a pole, daylight lasts about six months, followed by about six months of darkness.

The midnight sun is not every night of the year. It happens during the local summer. The same place can have very little daylight in winter.

Sort places by latitude

The lines separate three kinds of zone:

• Tropical: between the tropics, within about 23½° of the equator.
• Temperate: between a tropic and its polar circle.
• Polar: beyond a polar circle, toward a pole.

Find the latitude number, then compare it with 23½ and 66½. Singapore, near 1°N, is tropical. Chicago at 42°N and Brisbane at 27°S are temperate. Tromsø at 70°N is polar. The N or S chooses the hemisphere, but the same number limits work on both sides.

Latitude is one part of temperature

Low places in the tropics receive direct sunlight through the year. They stay warm or hot. Polar places receive less direct sunlight and are cold for much of the year. Temperate places usually have warmer and colder parts of the year.

Height matters, too. Mount Kilimanjaro is near 3°S, in the tropics. Its high summit is cold enough for snow and ice. A tropical location does not promise heat at every height.

Nor does the equator have every temperature record. Cloud and rain can limit heating there. Deserts farther away, such as Death Valley near 36°N, have recorded the highest air temperatures.

When night reaches your town, the Sun is still shining. Your part of Earth has turned away from its light.

One spin, one day

Earth rotates, or spins, on its axis from west to east. Seen from above the North Pole, that spin is counterclockwise. One full turn from one noon to the next takes 24 hours.

The Sun lights the half facing it. The other half faces away and has night. As Earth turns, places move into and out of the light. That creates their daily change from day to night.

Earth also travels around the Sun. That trip takes about a year, not a day. The daily spin is what brings your next sunrise.

Make a model

Use a globe, a sticker, and a lamp in a dim room. The lamp stands for the Sun. Mark a town with the sticker and keep the lamp still.

1. Turn the globe west to east. Look down from the North Pole to check the direction.
2. Watch the sticker enter the light. That is sunrise.
3. Keep turning until it is well inside the lit side.
4. Turn it across the edge into darkness. That is sunset.
5. Keep turning through the dark side until sunrise comes again.

The model shows why sunrise seems to come from the east. Earth turns eastward, making the Sun appear to move west across the sky. A moving car can make still trees seem to slide past. In a similar way, Earth's motion changes what you see.

Sun time and clock time

Solar noon is when the Sun reaches its highest point in your sky that day. Solar midnight is halfway through the night. At the same moment, solar noon and solar midnight fall along opposite meridians, 180° apart.

Clock noon is 12:00 p.m. Solar noon may happen at another clock time because a whole time zone shares one clock setting. Your town's Sun does not set that shared clock by itself.

Near the equator, daylight and darkness each last about 12 hours all year. Farther away, daylight hours change much more through the year. The summer midnight sun near a pole is an example of that difference.

A friend far away might be asleep while you eat lunch. You share one moment, but your towns face different directions toward the Sun.

A turning world has different sun times

Earth turns 360° in 24 hours. Divide the full turn by the hours:

Each hour, solar noon reaches meridians 15° farther west. A 30° gap means two hours of sun time. A 1° gap means four minutes, since an hour has 60 minutes.

Places east of you reach the same stage of the Sun's daily path sooner. Their sun time is ahead. Places west are behind. Different latitudes can still have different daylight lengths.

Work with Greenwich noon

Imagine the Sun is highest over Greenwich, at 0°. It is solar noon there. What is the sun time near Memphis, at 90°W?

1. Find the longitude gap: 90°.
2. Divide by 15° per hour.
3. The gap is six hours.
4. West is behind, so count six hours back from noon.

The sun time is about 6:00 a.m. At 45°E, the gap is three hours. East is ahead, so it is about 3:00 p.m. by the Sun. These are sun times, not the cities' official clock times.

Why towns stopped using separate times

Long ago, towns set clocks using their own solar noon. Two towns just 1° apart could have clocks four minutes apart. That was awkward when trains and telegraphs linked many towns. A train schedule needed a time that everyone along the route could use.

Time zones gave regions a shared clock. The zones did not make Earth have different times of day. Earth's rotation already did that. Zones organize those differences into clock settings people can share.

Keep latitude and longitude separate

Latitude helps you describe north–south position and sunlight zones. Longitude helps you compare sun time around the daily turn. Two places on one meridian share a sun time, even if one lies north of the equator and the other south. They can still have different daylight lengths.

A train cannot keep changing its timetable for every town's Sun. Time zones let a whole region share one clock setting.

From sun time to shared time

A time zone is an area using the same clock time. Standard time is its usual time setting before any daylight saving change. U.S. and Canadian railroads began using standard zones in 1883. The Greenwich meridian was chosen internationally the following year.

A simple world plan has 24 zones, each 15° wide. Moving to the next strip changes the clock by one hour. A strip centered on 0° would stretch from 7½°W to 7½°E.

Real borders bend around countries, states, and provinces. Governments choose shared times that help people work and travel together. Zones are not all neat strips of equal width.

Read a UTC offset

UTC, Coordinated Universal Time, is the reference for clock times. An offset tells you how far a clock is ahead of or behind UTC.

Tokyo uses UTC+9. New York uses UTC−5 during winter standard time. When UTC is noon, Tokyo is at 9:00 p.m. and New York at 7:00 a.m.

Greenwich Mean Time, or GMT, matches UTC for everyday time calculations. Greenwich uses GMT in winter. In summer its clocks use British Summer Time, UTC+1. A Greenwich clock does not stay on GMT all year.

Some offsets include minutes

India uses UTC+5:30. That means five hours and 30 minutes ahead, not five and thirty hundredths of an hour. Nepal uses UTC+5:45. Newfoundland's standard time is UTC−3:30.

Because of these smaller steps and other choices, the world has about 38 clock offsets in use, not exactly 24. They range from UTC−12 to UTC+14. The count can change when governments change their time rules.

On a time-zone map, find the colored area containing your town. Read its offset, then find the other town's area. Use the labels to compare them. Longitude alone cannot tell you a place's official offset.

To plan a call or a journey, match both places to the same moment. Write down their UTC offsets before doing any clock arithmetic.

Find which clock is ahead

A more positive offset is ahead. UTC+9 is ahead of UTC−8. UTC−5 is ahead of UTC−8 because it is closer to zero.

For opposite signs, add the sizes of the offsets. For two positive or two negative offsets, find their gap by subtraction. Include any minutes. Check the date after changing the clock.

New York in winter is UTC−5. London in winter is UTC+0. London is five hours ahead, so 9:00 a.m. in New York is 2:00 p.m. in London.

Cross midnight carefully

Los Angeles in winter uses UTC−8; Tokyo uses UTC+9. Their gap is 17 hours. At 3:00 p.m. Monday in Los Angeles, Tokyo is 17 hours ahead.

Count nine hours to midnight, then eight more. It is 8:00 a.m. Tuesday in Tokyo.

The 24-hour clock can help. Write 3:00 p.m. as 15:00. Add 17 to get 32. Subtract 24 to get 08:00 on the next day. Going backward past midnight gives the previous day instead.

Half hours work the same way. Mumbai at UTC+5:30 is five hours 30 minutes ahead of winter London. London noon is Mumbai 5:30 p.m.

Add journey time as well

A plane leaves Chicago at 6:00 p.m. in winter. Chicago is UTC−6; London is UTC+0. The flight lasts eight hours.

1. Add the flight's eight hours using Chicago's clock. It becomes 2:00 a.m. the next day.
2. London is six hours ahead. Add those six hours.
3. The plane arrives at 8:00 a.m. the next day, London time.

Changing zones alone tells you the destination's time at takeoff. Adding flight time alone gives arrival in the departure zone. You need both changes.

Check daylight saving time

Many places move clocks forward one hour in spring and back in fall. In the U.S., the change dates are the second Sunday in March and first Sunday in November. Hawaii and most of Arizona do not change. The UK uses UTC+1 from the last Sunday in March to the last Sunday in October. Southern Hemisphere places such as Sydney change in opposite parts of the year. Japan, China, and India keep their clocks unchanged.

Because the U.S. and UK change on different dates, their usual five-hour gap briefly becomes four hours. Check the offsets for the day of a real call. Across the date line, trust those offsets instead of the shortcut "east means ahead."

A calendar date needs a boundary somewhere on the globe. The International Date Line provides that boundary, mostly across the Pacific Ocean.

Why the date must change

Imagine going east through all 24 simple time zones. You move your clock ahead one hour in each. A complete trip adds 24 hours: a whole day. The date line balances that extra day when you cross it.

The line lies roughly along 180° longitude. It zigzags around islands and borders. A hemisphere boundary and a calendar boundary are different things. Samoa lies near 172°W, in the Western Hemisphere, yet west of the date line because the line bends around it.

Cross east or west

Crossing westward adds one calendar day. Monday becomes Tuesday. Crossing eastward subtracts one calendar day. Tuesday becomes Monday.

For a complete journey, include elapsed time and the clock changes too. UTC offsets already include the date-line difference. If you calculate with offsets, do not add another date-line day afterward.

Samoa uses UTC+13, and American Samoa uses UTC−11. Their gap is 24 hours. When American Samoa has 10:00 a.m. Tuesday, Samoa has 10:00 a.m. Wednesday. Same clock reading, different dates.

A flight that arrives earlier on the clock

A plane leaves Tokyo at 9:00 p.m. Tuesday. Its flight to Honolulu takes seven hours. Tokyo is UTC+9; Honolulu is UTC−10.

1. Add the flight in Tokyo time: arrival is 4:00 a.m. Wednesday.
2. Honolulu is 19 hours behind Tokyo.
3. Count back 19 hours: arrival is 9:00 a.m. Tuesday in Honolulu.

Seven real hours passed. The earlier local reading does not mean the plane flew backward in time.

A country can move its calendar

Samoa changed sides at the end of 2011 to match trading partners Australia and New Zealand. After Thursday, December 29, it went straight to Saturday, December 31. Friday, December 30, 2011, was skipped there.

Kiribati's Line Islands use UTC+14 and start each new day first. Baker and Howland Islands use UTC−12 and are among the last; nobody lives there. This 26-hour range means three dates can be in use at once for about two hours each day.

Jules Verne used world travel and calendar counting in Around the World in Eighty Days. The traveler Phileas Fogg thinks he is late, but his eastward journey has gained him a day.

A country can choose one shared time or several zones. Its east–west width helps explain why that choice matters.

Across the United States

The 50 states use six standard time zones. Read westward from Eastern time:

Including territories, U.S. law names nine zones in all. The six above describe the 50 states.

A game starting at 7:00 p.m. Eastern starts at 6:00 p.m. Central, 5:00 p.m. Mountain, and 4:00 p.m. Pacific. In winter, Hawaii is five hours behind Eastern time, so it starts at 2:00 p.m. there. In summer, Eastern clocks move forward but Hawaii's do not. The gap grows to six hours, making it 1:00 p.m. in Hawaii.

Half hours in Canada and Australia

Canada's six zones are Pacific, Mountain, Central, Eastern, Atlantic, and Newfoundland. Newfoundland standard time is UTC−3:30, half an hour ahead of Atlantic standard time. Toronto noon matches 1:30 p.m. in St. John's when both follow their usual matching seasonal clock settings.

Mainland Australia has three main standard offsets: Western UTC+8, Central UTC+9:30, and Eastern UTC+10. Some states change for daylight saving time, while others keep standard time. From early October to early April, the states and territories therefore use five main clock times.

One wide country, one clock

Russia uses 11 zones. China uses one official national time, UTC+8, even though it is very wide. In far western China, solar noon can be around 3:00 p.m. by the clock.

One national time makes shared schedules simple. Several zones keep local clocks closer to the Sun's daily path. Width does not force every country to make the same choice.

Find your own zone

Look up your town on a current time-zone map. Write its standard offset and check whether it uses daylight saving time. Then compare today's offset with a friend or relative's. Check the town, not just the country name: some countries contain several zones, and some regions change clocks while others do not.