2000 years ago, the indigenous people of what’s Ecuador today, knew there was something special about the Quito (center of the Earth) area.
1736, a French expedition established the equator line, which was reassured with modern day technology (difference is only 141 meters)
Sun solstice: no shadow can be seen for a few minutes
Sun equinox: sun will be exactly above the equator.
6 months of the year, the sun can be seen in the southern respectively northern skies. Stars of both skies can therefore be seen near the equator line.