Longitude has an impact on solar time. The Earth rotates once every 24 hours. The sun takes an hour to "travel" 15 degrees across the sky (the earth moves, but we see the sun move). This is called "solar time". Instruments on satellites and airplanes can measure solar time. They usually report their measurements in minutes past midnight at Greenwich, England.
Longitude also has an impact on local time. Local time is what seems to pass on Earth as day and night happen everywhere on our planet simultaneously. Because the moon causes tides, there are two types of tides: lunar and semilunar. Lunar tides occur when the moon is full and reaches its highest point in its orbit directly over a place on Earth. Semilunar tides occur when the moon is half-full or more and passes over a place on Earth twice each month.
Lunar and semilunar tides follow a rhythm based on the relative positions of the moon and the earth. At points along their orbits, the earth and moon are aligned such that both bodies experience the same force from the sun causing them to attract each other. This is called "syzygy". At one point during each lunar cycle (about 29 days), all of the points on Earth's surface are experiencing lunar syzygy.
Longitude and time have a strong connection. In 24 hours, the Earth completes one 360-degree revolution. It travels 15 degrees in an hour or one degree in four minutes. As a result, for one degree of longitude, there is a time difference of 4 minutes. Longitude increases as you go westward and southward from 0 degrees West to 180 degrees West. After that point, it decreases back to 0 degrees West.
At the equator, one minute of local time equals one second of true time. At the poles, one minute of local time equals two seconds of true time. At any other location on Earth, there is a variation of up to 10 minutes between the two times.
Time zones were invented by the British during the 19th century as a way to organize shipping routes and avoid conflict over territory. The idea was to create a common starting point for business meetings and other events that people across different countries could follow. This would allow people to plan activities around important dates such as holidays or sporting events.
In practice, time zones are used as a method of regulating local time, which varies due to sunlight exposure and other factors. Most countries use Greenwich Mean Time (GMT), which is recorded at the Royal Observatory in London.
Longitude and time are inextricably linked due to the earth's rotation. Local time (as determined by the location of the sun, for example) changes with longitude, with a 15-degree variation in longitude equivalent to a one-hour difference in local time. Longitudinal divisions of time are commonly referred to as "time zones". There are two types of time zones: standard and daylight.
The world is divided into five standard time zones, which are based on locations where there is an hour hand on the clock that is exactly opposite the hour hand on the clock at the prime meridian (0 degrees longitude). The international date line separates the western part of each zone from the eastern part of each zone.
There are also two types of daylight savings time periods: summer and winter. During these times, the hours of sunrise and sunset do not match up with civil twilight; instead, they fall on days when the sky is light enough during the middle of the day. Because farmers need sunlight to grow crops, they decide what role each region will play during daylight savings time. In spring, when it is not yet daylight savings time, places with daylight savings time have to switch their clocks forward one hour. In autumn, when it is already daylight savings time, places with daylight savings time can switch their clocks back one hour.
It takes 24 hours for the Earth to revolve 360 degrees (longitude). As a result, a one-hour gap exists between two locations separated by 15 degrees of longitude. This amounts to a 24-hour difference, or one day, between east and west of the 180-degree line of longitude.
The date line is drawn as a straight line on a map, but on the surface of the earth it follows the path of a magnetic pole. The last time a major geographic feature was moved with respect to longitude was when America was granted its independence in 1776. At that time, both the United States and France agreed to assign three months back-to-back as the date line passed between them. These dates were considered official entries on world clocks until 1923 when Britain inherited its role as keeper of the clock from the British Empire. Since then, the date line has remained still.
In 1945, the United Nations decided to assign days of the week and months of the year for use around the world. Since then, the only real change has been which country gets Monday. Before 1945, most countries got their week on a national basis so they would always align with Europe or America. After 1945, countries could choose whether to keep their current week or swap days about every other month.
Since 1971, when the UN approved a plan to divide the date line into two sections of 45 degrees each, all countries have been allowed to make this choice.
It takes the Earth 24 hours to complete one rotation or 360 degrees of longitude. This indicates that every hour, the Earth travels 15 degrees longitude. One degree of longitude takes 4 minutes to complete (1 hour = 60 minutes divided by 15 degrees each hour = 4 minutes per longitude). The time interval between two longitudes is therefore about 4 minutes.
The word "longitude" comes from a Latin word meaning "east-west." The first longitude was determined by William Harrison in England in 1714 and the second by Jeremiah Horrocks in England in 1669.
Longitudes are used to determine where on Earth an object is located with respect to east or west. For example, ships use their positions relative to various landmarks to determine their exact longitude at any given moment. Scientists use longitudes when trying to position themselves geographically within specific regions of the world.
An object's latitude is measured as the angle between the equator and the north or south pole and varies depending on your location across the surface of the planet. Longitude is measured as the angle between 0 and 90 degrees east or west from a fixed point around the globe called Greenwich Mean Time (GMT). The first global radio navigation system developed in the 1950s used longitudes to indicate where on Earth planes were flying and helped create the basis for today's commercial aviation system.