Circle of latitude

Lines go around the Earth.

These lines are called latitude. They run from east to west.

One big line is the Equator.

It is the longest line. It sits in the middle of Earth.

Some lines mark special zones. The Arctic Circle is near the top.

The Antarctic Circle is near the bottom.

These lines can be borders. They can separate different lands. People use them on maps to show where to go.

Can you find these lines on a map?

Lines of latitude go around the Earth from east to west.

These lines are also called parallels. This is because they never touch each other. They stay the same distance apart.

The Equator is the most important line.

It sits at 0 degrees. It is the longest line on Earth. It splits the world into two halves. We call these the Northern and Southern Hemispheres.

There are five major circles of latitude. They help mark special zones on our planet. The Arctic Circle is near the North Pole.

The Antarctic Circle is near the South Pole. The Tropic of Cancer and Tropic of Capricorn are also important. They mark where the Sun can be directly overhead.

People use these lines for many things. They can act as borders between countries. For example, the 49th parallel is a border for Canada and the USA. In the US, lines also make borders for states like Colorado. These lines help us know exactly where we are on the globe.

A circle of latitude is an imaginary line that runs east to west around the Earth.

These lines are often called parallels. This name comes from the fact that they never touch or cross each other. If you imagine these lines as flat planes, they would stay perfectly apart. A location's position on these circles is found using longitude. Unlike lines of longitude, latitude circles change in size. They get smaller as you move away from the Equator toward the poles. The Equator is the longest circle of all. It is the only one that is a "great circle," meaning its center is the center of the Earth.

Measuring latitude is like measuring an angle. The latitude is the angle between the Equator and the circle. The center of this angle is the very center of the Earth. The Equator sits at 0 degrees. The North Pole is at 90 degrees north. The South Pole is at 90 degrees south. There are 89 whole degree circles between the Equator and each pole. Scientists can be even more precise with these measurements. They use decimal degrees, like 34.637° N. They can also use minutes and seconds, like 22°14′26″ S.

There are five major circles of latitude that mark special zones. The Equator divides the world into the Northern and Southern Hemispheres.

The Arctic Circle is the southernmost latitude in the north. At this line, the Sun can stay above the horizon for 24 hours during the June solstice.

The Antarctic Circle does the same thing in the south.

The Tropic of Cancer and the Tropic of Capricorn mark where the Sun can be directly overhead. The Tropic of Cancer is in the north.

The Tropic of Capricorn is in the south.

The positions of these major circles are not perfectly fixed. They depend on the tilt of the Earth's axis. This tilt changes slowly over a very long time. The main cycle causes the tilt to change every 41,000 years. Because of this, the Tropical Circles drift toward the Equator. The Polar Circles drift toward the poles by about 15 meters every year. There are also smaller shifts caused by things like nutation. Nutation is a short-term change that happens every 18.6 years. Even the Earth's rotation causes tiny fluctuations called polar motion. These movements are very small, but they do affect the lines.

People use these circles to make borders on maps. Sometimes, lines are used when there are no natural borders like rivers. In 1884, the Berlin Conference used these lines to draw borders in Africa. Many places in North America also use them. The 49th parallel is a famous border between Canada and the United States. In the US, the northern border of Colorado is at 41° N. The southern border of Colorado is at 37° N. Historically, the 36°30′ N line was used as the Missouri Compromise line.

These lines help us organize the world into clear pieces.

A circle of latitude is an abstract east-west line around the Earth.

These lines are often called parallels. This name comes from the fact that they never intersect each other. If you imagine the planes containing these circles, they stay perfectly apart. A location's position along a circle of latitude is given by its longitude. Unlike circles of longitude, which are all great circles, latitude circles change in size. They get smaller as the distance from the Equator increases. The Equator is the longest circle of latitude. It is also the only one that is a great circle. This means its center is the center of the Earth.

Measuring latitude is like measuring an angle. The latitude of a circle is the angle between the Equator and that circle. The vertex of this angle is at the center of the Earth. The Equator is located at 0°. The North Pole is at 90° north. The South Pole is at 90° south. There are 89 integral circles of latitude between the Equator and the poles in each hemisphere. Scientists use more precise measurements to locate places. They may use decimal degrees, such as 34.637° N. They might also use minutes and seconds, such as 22°14′26″ S.

Five major circles of latitude define the Earth's principal geographical zones. The Equator is fixed at 90° from the Earth's axis of rotation. It divides the world into the Northern and Southern Hemispheres. The Arctic Circle is the southernmost latitude in the Northern Hemisphere where the Sun stays above the horizon for 24 hours during the June solstice.

Similarly, the Antarctic Circle marks the northernmost latitude in the Southern Hemisphere where the Sun stays above the horizon for 24 hours during the December solstice.

The Tropic of Cancer is the northernmost latitude where the Sun can be seen directly overhead at the June solstice.

The Tropic of Capricorn is the southernmost latitude for this same event during the December solstice.

The positions of these major circles are not perfectly fixed. They depend on the Earth's axial tilt relative to its orbit. This tilt is called the obliquity of the ecliptic. If the Earth were upright, these special circles would not exist. The axial tilt changes through several different cycles. One long cycle causes the tilt to fluctuate between 22.1° and 24.5° every 41,000 years. Currently, the average tilt is decreasing by about 0.468″ per year. This causes the Tropical Circles to drift toward the Equator. The Polar Circles drift toward the poles by about 15 meters per year.

Other smaller motions also affect these lines. Nutation is a short-term variation in the tilt. Its main period is 18.6 years with an amplitude of 9.2″. This can cause shifts of almost 300 meters north or south. There is also a phenomenon called polar motion. This is when the Earth's rotational axis undergoes small fluctuations. These fluctuations are on the order of 15 meters. While these movements are small, they do cause theoretical shifts in the parallels. These shifts occur if the given axis tilt were maintained throughout the entire year.

Humans often use these circles to create borders. This is common when there are no natural borders like mountains or rivers. During the 1884 Berlin Conference, massive scales of borders were drawn in Africa using these lines. Many North American borders also follow circles of latitude. For example, the 49th parallel is a major border between Canada and the United States. In the United States, the northern border of Colorado sits at 41° N. The southern border of Colorado is at 37° N. Historically, the 36°30′ N line was used as the Missouri Compromise line.

Latitude circles also appear differently depending on map projections. On a Mercator projection, these circles are perpendicular to all meridians. On a Gall-Peters projection, they are also perpendicular to meridians. On an equirectangular projection, they are horizontal and equally spaced. However, on other projections, the spacing may change to show different information. The Mercator projection spaces them more widely near the poles. This helps preserve local shapes and scales. The Gall-Peters projection spaces them more closely near the poles. This allows for more accurate comparisons of area. On many other projections, the circles are neither straight nor parallel.