The imaginary line running from Earth’s North Pole to its South Pole is called its axis. More precisely, it is Earth’s axis of rotation, the invisible line around which the planet spins.
The axis passes through Earth’s centre and meets the surface at the geographic North and South Poles. Earth completes one rotation relative to the distant stars in about 23 hours, 56 minutes, and 4 seconds; the familiar 24-hour solar day is slightly longer because Earth also moves along its orbit around the Sun.
The axis is not perfectly upright relative to Earth’s orbit. It is tilted by about 23.4 degrees, and that tilt produces the seasons as Earth travels around the Sun. A common mix-up is confusing the axis with the equator: the axis is a pole-to-pole line, while the equator is an imaginary circle halfway between the poles. Earth’s axis also slowly wobbles, completing a cycle of precession in roughly 26,000 years.