1. Equator: This is the imaginary line that circles the Earth at 0 degrees latitude, dividing it into the Northern and Southern hemispheres. It's the widest part of the Earth and receives the most direct sunlight.

2. Tropic of Cancer: This line lies at 23.5 degrees north of the Equator. It marks the northernmost point where the sun can be directly overhead at noon during the summer solstice.

3. Tropic of Capricorn: This line lies at 23.5 degrees south of the Equator. It marks the southernmost point where the sun can be directly overhead at noon during the winter solstice.