Here’s something I actually had seldom thought about: what is the equator? Generally, it is “the intersection of the surface of a rotating sphere with the plane that is perpendicular to the sphere’s axis of rotation and midway between its poles.
“The latitude of the Earth’s equator is by definition 0° (zero degrees) of arc. In the cycle of Earth’s seasons, the plane of the equator passes through the Sun twice per year: at the March and September equinoxes. To an observer on the Earth, the Sun appears to travel North or South over [it]… at these times. Light rays from the center of the Sun are perpendicular to the surface of the Earth at the point of solar noon on the Equator.”
There are several countries that cross the imaginary line. Starting at the Prime Meridian and heading east:
In Africa: São Tomé and Príncipe, Gabon, Republic of the Congo, Democratic Republic of the Congo, Uganda, Kenya, Somalia
In Asia: Indonesia, several times, including Sumatra and Borneo
Oceania: Passing between Aranuka and Nonouti atolls, Kiribati (at 0°0′N 173°40′E)
In South America: Ecuador (of course!), Colombia, Brazil
Interestingly to me, Equatorial Guinea is NOT touched by the line. It gets as close as 3°45′N 8°47′E.
National Geographic provides more facts:
The Earth is widest at its Equator. The distance around the Earth at the Equator, its circumference, is 40,075 kilometers (24,901 miles).
The Earth’s diameter is also wider at the Equator, creating a phenomenon called an equatorial bulge… The Earth’s diameter at the Equator is about 12,756 kilometers (7,926 miles). At the poles, the diameter is about 12,714 kilometers (7,900 miles). The Earth’s equatorial bulge is about 43 kilometers (27 miles).
The equatorial bulge means that people standing at sea level near the poles are closer to the center of the Earth than people standing at sea level near the Equator. The equatorial bulge affects the ocean, too — sea levels are slightly higher in equatorial regions than near the poles.
The equatorial bulge is created by the Earth’s rotation.
The slightly weaker gravitational pull and momentum of the spinning Earth makes equatorial regions ideal places for space launches. It takes an enormous amount of energy to launch a satellite or other spacecraft out of the Earth’s atmosphere. It takes less energy (rocket fuel) to launch in lower gravity.