Tides are defined as the regular rise and fall of ocean water above or below mean sea level. Depending on where a person is on Earth, and the position of the Earth, moon, and sun relative to each other, tides will vary. For this reason, most parts of the world publish tide charts, in the form of a small table which outlines the expected times for high and low tide through the day. Usually, a tide chart includes the estimated height of each tide, along with the times of sunrise and sunset, along with moonrise and moonset. By using the data in a tide chart, people who work with the ocean can have safer and more productive days.
A proper tide chart is a vital navigational aid, especially when maneuvering large ships close to shore or into harbor. A miscalculation in the tides could result in a catastrophic accident such as a collision with a bridge or running aground. Sailors making day trips, such as fishermen who go out every day, have tide charts relevant to their local area to assist them in deciding when to go out and where to travel. Larger ships traveling around the world often take advantage of computerized tide charts, which can display data for any location in the world.
Tides are caused by the gravitational pull of the moon and sun on the water which covers the Earth. Because the positions of all three bodies can be easily projected, scientists can predict the tidal patterns for an area and create a tide chart. A tide chart also takes the topography and history of the region into account, and is a very specific document designed to be used in a small area. Generally, there are four tides a day: two high tides, and two low tides. The variation in height between the tides depends on location, season, and astronomical phenomena; sometimes the variation is only a few feet, while on other occasions it has been recorded to be as much as 50 feet (15 meters). In most cases, a tide chart will also include a graph to help readers visualize the differences between the tides.
Usually, a tide chart will be published for a general region with a list of corrections for specific areas in the front. For example, you may need to add or subtract minutes to the time to get an accurate estimate of when a high or low tide is going occur. In addition, there may be variances in height, which are also listed in the regional corrections. When reading a tide chart for a region, first check to see if you need to make corrections, and then open it to the relevant day. Make any adjustments needed for an accurate reading, and plan your day accordingly.