Final answer:
The equator is the invisible line that runs around the middle of the Earth, dividing it into two halves—the Northern and Southern Hemispheres.
Step-by-step explanation:
The invisible line that runs right around the Earth's middle, dividing it into two halves, is called the equator. The equator is a great circle equidistant from the North and South Poles, dividing the Earth into the Northern and Southern Hemispheres. This line is key in the grid of imaginary lines geographers use, including latitude and longitude, to pinpoint locations on the planet.
Just as the Earth has an equator, so too does the celestial sphere—an imaginary projection of space—have a celestial equator. The celestial equator is a projection of the Earth's equator into space and lies halfway between the celestial poles, which correspond to the Earth's actual North and South Poles. This helps astronomers and navigators orient themselves in relation to the stars and planets.