In general, an imaginary line is usually any sort of geometric line that has only an abstract definition and does not physically exist. In fact, they are used to properly identify places on a map.
Some outside geography does exist, such as the Mendoza Line, which in baseball divides below-average hitters and extremely poor hitters. A centerline is a nautical term for a line down the center of a vessel lengthwise.
Geography
As a geographical concept, an imaginary line may serve as an arbitrary division, such as
Antarctic Circle,
Arctic Circle,
Border,
International Date Line,
Latitude, including the Equator,
Longitude, the prime meridian, the Tropic of Capricorn, and the Tropic of Cancer. Any axis about which an object spins is an imaginary line.
Mason–Dixon Line, which informally marks pieces of the borders of four U.S. states: Delaware, Maryland, Pennsylvania, and West Virginia, once part of Virginia. Symbolically, the line separates the American North from the American South,
Missouri Compromise Line,
Time zones.
Glossary
Axis of the Earth
An imaginary straight line running through the center of the Earth from the North Pole to the South Pole. The earth is said to rotate (spin) on this axis, which is “tilted” in relation to the sun. This causes our seasons.
Day Length
Also known as photoperiod. The length of time between sunrise and sunset.
An international time-keeping standard based on the local time in Greenwich, England (0 degrees longitude). GMT or UT enables us to refer to things that happen at the same moment in different time zones. (It would be confusing to use “local time.”) At any moment, GMT/UT is the same everywhere on Earth. (That’s why it’s called universal time.) What time is it now? Check the Greenwich Mean Time clock.
Hemisphere
A mapping division means half of the Earth (sphere). First, picture cutting the earth in half at the equator (0 degrees latitude).
This divides the Earth into the Northern Hemisphere (north of the equator) and the Southern Hemisphere (south of the equator).
These are labeled in yellow on the illustration. Next picture cutting the earth in half at the Prime Meridian (0 degrees longitude).
This divides the Earth into the Western Hemisphere (west of the Prime Meridian) and the Eastern Hemisphere (east of the Prime Meridian). These are labeled in red on the illustration.
Latitude
Imaginary horizontal mapping lines on the Earth. They are known as “parallels” of latitude because they run parallel to the Equator. The number of degrees of latitude shows how far north or south of the Equator a specific location is.
Longitude
Imaginary vertical mapping lines on Earth are known as “meridians” of longitude. The number of degrees of longitude shows how far east or west of the Prime Meridian a specific location is.
Meridian
An imaginary line that runs vertically, north and south, from the North Pole to the South Pole. All points on a meridian have the same longitude.
Photoperiod
Also called day length. The length of time between sunrise and sunset.
Prime Meridian:
The Prime Meridian serves as the starting point for longitude measurement, so is indicated as 0 degrees longitude. The Prime Meridian passes directly over the British Royal Observatory in Greenwich, England. (See illustration, above.)
Revolution of the Earth
The yearly 365 1/4 days trip the Earth takes around the sun. We experience different seasons as the tilted Earth revolves around the sun.
Rotation of the Earth
The spinning or turning of the earth on its axis. The Earth makes one complete rotation every twenty-four hours.
Solstice
The word means “sun stop.” It refers to the two moments each year when the sun appears to be farthest from the equator. On the winter solstice in our hemisphere (around December 22), the sun seems to reach its most southerly point. It is our shortest day of the year. From there, it seems to head north until it reaches its most northerly point. That is our summer solstice (around June 21): the longest day of the year. When the Northern Hemisphere has its summer solstice, the Southern Hemisphere has its winter solstice and vice versa. The sun doesn’t really move, but it looks like it does to us.
Twenty-Four Hour Clock
Instead of keeping time on the basis of 12 a.m. hours and 12 p.m. hours, the 24-hour clock runs straight through. It begins at 00:00 (midnight) and runs to 23:59 (11:59 PM). This is also known as “military time.”
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an imaginary line around which the earth rotates
The Earth is the 3rd planet from the Sun. It supports life because it has water and oxygen. It has a protective atmosphere that blocks out most of the Sun’s damaging rays and protects it from small objects floating in space. It is made mostly of rock. The Moon revolves around Earth (it is a satellite of Earth). It is 240,000 miles away and is ¼ the size of Earth. There is NO atmosphere. It has no air, wind, or liquid water. It reflects the light of the Sun. The Sun is made of hot, glowing gases. It is about 93 million miles away.
EARTH’S ROTATION
Rotation = A single complete turn The Earth rotates on an imaginary line called an axis, which runs through Earth from the North Pole to the South Pole. The rotation of the Earth causes day and night. One complete rotation of the Earth takes 24 hours or 1 day As it rotates, one side of Earth faces the sun. This side has daytime. The side of Earth facing away from the sun has nighttime.
EARTH’S REVOLUTION AROUND THE SUN
Gravity pulls Earth toward the Sun, holding it in orbit. Orbit is the path that an object takes around another object. Earth revolves or travels around the Sun. It takes Earth about 365 days or 1 year to complete one revolution around the Sun. Earth rotates on a tilted axis. Earth’s axis is always tilted in the same direction. The Earth has seasons because it revolves around the Sun on a tilted axis. The Earth is divided into halves called hemispheresThe Northern Hemisphere extends from the equator to the North Pole. The Southern Hemisphere extends from the equator to the South Pole. The part of the Earth that tilts toward the Sun will get more direct sunlight and will experience summer. The part of the Earth that tilts away from the Sun will get less direct sunlight and will experience winter.
Earth’s Revolution
For Earth to make one complete revolution around the Sun takes 365.24 days. This amount of time is the definition of one year. The gravitational pull of the Sun keeps Earth and the other planets in orbit around the star. Like the other planets, Earth’s orbital path is an ellipse so the planet is sometimes farther away from the Sun than at other times. The closest Earth gets to the Sun each year is at perihelion (147 million km) on about January 3rd and the furthest is at aphelion (152 million km) on July 4th. Earth’s elliptical orbit has nothing to do with Earth’s seasons.
During one revolution around the Sun, Earth travels at an average distance of about 150 million km. Earth revolves around the Sun at an average speed of about 27 km (17 mi) per second, but the speed is not constant. The planet moves slower when it is at aphelion and faster when it is at perihelion. During the Northern Hemisphere summer, the North Pole points toward the Sun, and in the Northern Hemisphere winter, the North Pole has tilted away from the Sun.
Earth’s Motions
Imagine a line passing through the center of Earth that goes through both the North Pole and the South Pole. Earth spins around its axis, just as a top spins around its spindle. At the same time that the Earth spins on its axis, it also orbits or revolves around the Sun. A pendulum set in motion will not change its motion, and so the direction of its swinging should not change. However, Foucault observed that his pendulum did seem to change direction.
Since he knew that the pendulum could not change its motion, he concluded that the Earth, underneath the pendulum was moving. An observer in space will see that Earth requires 23 hours, 56 minutes, and 4 seconds to make one complete rotation on its axis. But because Earth moves around the Sun at the same time that it is rotating, the planet must turn just a little bit more to reach the same place relative to the Sun. Hence the length of a day on Earth is actually 24 hours. At the equator, the Earth rotates at a speed of about 1,700 km per hour, but at the poles, the movement speed is nearly nothing.