Why Day in North America Means Night in China

Earth's rotation on its axis causes day/night cycles. When North America faces the Sun, China faces away—it's on the opposite side of the planet.

Additional factors:

• Axial tilt (23.5°): Causes seasons; summer = longer days in Northern Hemisphere.
• Elliptical orbit: Earth's distance from Sun varies (perihelion/aphelion), slightly affecting daylight intensity but not the basic day/night cycle.

The core reason for simultaneous day/night opposition is simply spherical Earth rotating once every 24 hours.