international date line | NOAA Teacher at Sea Blog
The International Date Line (IDL) is an imaginary line on Earth's surface located at Time Zone Converter · International Meeting Planner · Event Time The International Date Line is located halfway around the world from the prime meridian (0° three different dates on the calendar are in use at the same time on Earth. This lesson will explain what the International Date Line is, how it Did you know there is a place on Earth where you can go back in time? Okay The Prime Meridian (center red line) and International Date Line (red line at right). .. Choose a goal, Study for class, Earn college credit, Research colleges. Earth's lines of longitude (meridians) are great circles that meet at the north and E and ° W from the prime meridian is termed the international dateline.
Conventionally, the IDL is not drawn into Antarctica on most maps. The IDL must therefore be observed in conjunction with the Earth's time zones: Facts dependent on the IDL[ edit ] For the two hours between For example, at During the first hour UTC During the second hour UTC These include portions of the Republic of Kiribatiincluding Millennium Island in the Line Islandsas well as Samoa during the southern summer.
As a result, this atoll was renamed Millennium Island. At the equinoxesthe first place to see daylight would be the uninhabited Millennium Island in Kiribati, which is the easternmost land located west of the IDL.
All nations unilaterally determine their standard time zonesapplicable only on land and adjacent territorial waters.
International Date Line
This date line can be called de facto since it is not based on international law, but on national laws. These national zones do not extend into international waters.Earth, Parallels and Meridians, Latitude and Longitude [IGEO TV ]
The nautical date linenot the same as the IDL, is a de jure construction determined by international agreement. It is the result of the Anglo-French Conference on Time-keeping at Seawhich recommended that all ships, both military and civilian, adopt hourly standard time zones on the high seas.
The United States adopted its recommendation for U. This date line is implied but not explicitly drawn on time zone maps. In reality, ships use these time zones only for radio communication and similar purposes. For internal purposes, such as work and meal hours, ships use a time zone of their own choosing. Cartographic practice and convention[ edit ] The IDL on the map on this page and all other maps is based on the de facto line and is an artificial construct of cartographers, as the precise course of the line in international waters is arbitrary.
Similarly, the western Aleutian Islands are islands of American date in a sea of Asian date. No international organization, nor any treaty between nations, has fixed the IDL drawn by cartographers: The conference resolved that the Universal Day, midnight-to-midnight Greenwich Mean Time now known as Coordinated Universal Time, or UTCwhich it did agree to, "shall not interfere with the use of local or standard time where desirable".
The Philippine Islands are shown pre, while Alaska is shown post Philippines and [ edit ] As part of New Spainthe Philippines long had its most important communication with Acapulco in Mexico and was accordingly on the east side of the IDL despite being at the far western edge of the Pacific Ocean.
From tothe Philippines was one day behind its Asian neighbors Saturday, 16 March was the first European visit, when Ferdinand Magellan claimed the area for Spain; colonization began on Friday, 27 April After Mexico gained its independence from Spain inPhilippine trade interests turned to Imperial Chinathe Dutch East Indies and adjacent areas, so the Philippines decided to shift back to the west side of the IDL by removing Tuesday, 31 December from its calendar.
Western publications were generally unaware of this change until the early s, so erroneously gave the International Date Line a large western bulge for the next half century. The United States purchased Russian America while based in the contiguous United Statesfrom the east with its own Gregorian calendar adopted in while several British colonies.
Senator Charles Sumner stated during his three-hour ratification speech an encyclopedic discussion of Russian America on Tuesday, 9 Aprilthat this day of the week and calendar discord should be changed. Sitka mean solar time time zones were not yet in use that was the date and time that Alaska changed from an Asian and Julian date to an American and Gregorian date.
If the transfer had occurred at the preceding midnight then Friday, 6 October Julian would have been followed by Friday, 18 October Gregoriana duplicate day with a day difference appropriate both for changing from an Asian date to an American date equivalent to moving the IDL from the east to the west of Alaska and for changing from the Julian calendar to the Gregorian calendar during the 19th century.
In that year, King Malietoa Laupepa was persuaded by American traders to adopt the American date three hours behind California to replace the former Asian date four hours ahead of Japan. Being 21 hours behind made business difficult because having weekends on backward days meant only four days of the week were shared workdays. Tokelau is a territory of New Zealand north of Samoa whose principal transportation and communications links with the rest of the world pass through Samoa.
During that period it was west of the IDL. Because of that, Kwajalein used the Hawaiian date, so was effectively east of the International Date Line unlike the rest of the Marshalls.
Kwajalein returned to the west side of the IDL by removing Saturday, 21 August from its calendar to match the dates used by the rest of the Marshall Islands, at the request of its government. Along with the shift, Kwajalein's work week was changed to Tuesday through Saturday to match the Hawaiian work week of Monday through Friday on the other side of the IDL. As a result, the country straddled the IDL. Government and commercial concerns on opposite sides of the line could only conduct routine business by radio or telephone on the four days of the week which were weekdays on both sides.
To eliminate this anomaly, Kiribati introduced a change of date for its eastern half by removing Saturday, 31 December from its calendar. After the change, the IDL in effect moved eastwards to go around the entire country.
Strictly legal, the nautical IDL convention is still valid. When the land time zone says it's Monday, these islands would form enclaves of Monday in an ocean which has Sunday. Maps are usually not drawn this way. Date lines according to religious principles[ edit ] Further information: Christmas for example, is celebrated on 25 December according to either the Gregorian or the Julian calendardepending upon which of the two is used by the particular church as that date falls in countries located on either side of the Date Line.
A problem with the general rule above arises in certain Christian churches that solemnly observe a Sabbath day as a particular day of the week, when those churches are located in countries near the Date Line.
An echogram taken from the Oscar Dyson. Shades of yellow and red show extremely large, dense schools of fish. The solid red at the bottom of the picture is the bottom of the sea which is at Another piece of the puzzle… how reflective an individual fish is to sound waves.
How many hours is the prime meridian from the international date line
This is called target strength. Each fish reflects sound energy sent from the transducers, but why? For fish, we rely on the swim bladderthe organ that fish use to stay buoyant in the water column. Since it is filled with air, it reflects sound very well. When the sound energy goes from one medium to another, there is a stronger reflection of that sound energy. The bigger the fish, the bigger the swim bladder; the bigger the swim bladder, the more sound is reflected and received by the transducer.
We call this backscatter, or target strength, and use it to estimate the size of the fish we are detecting. This is why fish that have air-filled swim bladders show up nicely on hydroacoustic data while fish that lack swim bladders like sharksor that have oil or wax filled swim bladders like Orange Roughy have weak signals.
X-ray of fish showing the presence of a swim bladder courtesy of DeAnza College. Target strength is how we determine how dense the fish are in a particular school.
Scientists take the backscatter that we measure from the transducers and divide that by the target strength for an individual and that gives you the number of individuals that must be there to produce that amount of backscatter. We extrapolate this information to all the area of the Bering Sea to estimate the pollock population. A close look at part of Transect In this echogram, the area backscatter numerical values are included.
At the top of the water column, you can see what are probably jellyfish which have little backscatter since they have no swim bladders.
Along the bottom are groundfish. In the center of the water column are several large schools of Walleye pollock with strong backscatter. The square that has a value of In doing so, you get a complete picture of the Walleye pollock population in the Bering Sea. This is the combination of hydroacoustic data and biological trawl data analyzed to show what the entire walleye pollock population looked like for courtesy of the Alaska Fisheries Science Center www. Analysis is still being done on the current survey.
Scientists ALSO use hydroacoustic data when trawling to determine if they have caught a large enough sample size to collect fish length data to validate their target strength data. Since the scientists only need about fish for a statistically significant sample, they watch this screen carefully so that they do not take more fish than they need.
Sometimes, we are only officially fishing for 5 minutes if we pull through a large school. What are the data telling us? The Walleye pollock data suggest that the population is currently stable; however, there is some evidence of pollock in waters that have traditionally been north of their uppermost documented population range.
Are warmer waters due to climate change to blame for this possible shift? Here is an interesting article that addresses this issue and raises several other trends regarding pollock population response to changes in food source and predation due to climate change.
Click on the picture to open the article! How might climate change affect fish sticks? Click on the picture to read more! The economic and ecological implications of a shifting pollock population range are a bit unsettling.
Fish do not know political boundaries.