Why are there red and green lights on ships, aircraft and even spacecraft?

Why are there red and green lights on ships, aircraft and even spacecraft?

The convention of using red lights to indicate the port side and green lights to indicate the starboard side comes from the maritime tradition, and very likely green was starboard because the safe side, being the steering side.

The red and green lights on ships, aircraft, and spacecraft are navigation lights, also known as sidelights. They help indicate the direction in which a vehicle is moving to other vehicles and observers. The red light is placed on the port (left) side, while the green light is on the starboard (right) side. This system aids in determining the direction of travel and helps prevent collisions, especially in low visibility conditions.