The ocean is never still. Waves are most commonly caused by wind. Wind-driven waves, or surface waves, are created by the friction between wind and surface water. The gravitational pull of the sun and moon on the earth also causes waves. These waves are tides or, in other words, tidal waves. It is a common misconception that a tidal wave is also a tsunami. The cause of tsunamis are not related to tide information at all but can occur in any tidal state.
Before the development of clearly defined ports, mariners were guided by fires built on hilltops. Since raising the fire would improve the visibility, placing the fire on a platform became a practice that led to the development of the lighthouse. In antiquity, the lighthouse functioned more as an entrance marker to ports than as a warning signal for reefs and promontories, unlike many modern lighthouses. The most famous lighthouse structure from antiquity was the Pharos of Alexandria, Egypt, although it collapsed during an earthquake centuries later.
The word « ocean » comes from the figure in classical antiquity, Oceanus, the elder of the Titans in classical Greek mythology, believed by the ancient Greeks and Romans to be the divine personification of the sea, an enormous river encircling the world. Although many people believe that the oceans are blue because the water reflects the blue sky, this is actually not true. Water has a very slight blue color that can only be seen when there is a lot of water. However, the main cause of the blue or blue/green color of the oceans is that water absorbs the red part of the incoming light, and reflects the green and blue part of the light. We then see the reflected light as the color of water.
