A line is imagined around the earth in east-west at equal distances from the north pole and south pole. This line is called the equator. Equinox is also known as equator , equatorial circle , elliptical circle , guru circle etc. This line is called the elliptical , because the equator is the largest of the lines encircling east-west. This line is the largest axis and the circumference of the earth is measured along this line.