What is a Great circle?

A great circle is a circle that is drawn on the surface of a sphere (such as Earth) that has a radius equal to the radius of the sphere, and whose center is also the sphere�s center. The Equator is the only latitude that is a great circle. All longitudes are a part of a great circle.

Equator

Circles that do not pass through the center of the Earth are small circles. All the parallels of latitudes other than the Equator are small circles. Arcs of great circles are the shortest route between two points on a sphere.

Characteristics:

1. A great circle is a theoretical circle formed by the intersection of the Earth�s surface and an imaginary plane that passes through the center of the Earth and divides it into two equal parts. The Equator is the largest possible circle among the lines on the latitude.

2. All such circles must pass through or touch the center of the circle. The Equator and all diagrammatically opposite longitudes touch the center of a circle and therefore are Great Circles.

3. The infinite number of circles that touch the two opposite ends of the sphere can be drawn on a sphere.

4. Intersecting great circles always bisect each other.

5. Great circles are used by navigators to find the shortest distance between any two points on the Earth�s surface.

Do you know what is this shortest distance called?

It is called the Great Circle Route. It is the shortest distance between two places on the Earth and lies on the arc of a great circle. Using this hypothesis, the shortest route from New York to Moscow would be over the North Pole. There are several which are not taken into account while finding the Great Circle Route which are:

Restrictions such as weather or political restrictions are imposed by the countries concerned.
� Lack of landing and take-off facilities for airplanes.

Great Circle Route

(ii) Great Circle routes are especially important for places that are on opposite sides of the globe. Most globes show great circle routes between distant ports across the Atlantic, the Pacific, and the Indian Ocean.
(iii) Great circles are used by meteorologists to determine climate and weather conditions in a region.

Do you know who are meteorologists?

Meteorologists are the scientists who study the weather. They can be weather presenters or sole researchers.

Questions:

1. How many circles touch the two opposite ends of the sphere and can be drawn on a sphere?
a. Two
b. Three
c. Four
d. Infinitely many

2. Intersecting great circles always ____________
a. Trisect each other
b. Touch each other
c. Cross each other
d. Bisect each other

3. What are the scientists who study the weather called?
a. Astronauts
b. Paleontologists
c. Archaeologists
d. Meteorologists

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