An imaginary line that passes through Earth's center and its North and South Poles
the 23.5 degree tilt on Earth's axis, reason why we have seasonal changes
The spinning of Earth on its axis
the apparent path of the Sun across the sky
sometimes called the twilight zone or "grey line," is a moving line that marks the illuminated day side and the dark night side of a planetary body such as moons or planets.
A tool for observing distant objects.