How is longitude calculated

Determining latitude was relatively easy because it could be calculated from the altitude of the sun at noon but for longitude, early navigators had to rely on dead reckoning. This was inaccurate on long voyages out of sight of land and a solution to the problem of accurately calculating longitude eluded navigators for many centuries until John Harrison invented the chronometer in the 18th.

Harrison was tempted by the prize and set out to produce an accurate timepiece which could be used to compare local time to Greenwich time which the timepiece would be set to. He completed his chronometer in after several previous attempts and this proved to be so successful that it was used by Captain Cook in his voyages after Angular distance between meridians of longitude.

Since the Equator is a great circle, 1 o will subtend an arc of: Since 1 o subtends an arc of 60 n. Time difference between meridians of longitude. We know that the Earth revolves about its axis once every 24 hours.

In other words, the Sun completes its apparent revolution of o in 24 hours. This means that the Sun crosses each of the meridians of longitude once every 24 hours. From this, it becomes obvious that there is a direct relationship between arc and time such that 1 minute of time equals 15 minutes of arc.

Calculating longitude by comparing time difference. If we have two accurate clocks, one calibrated to GMT and the other calibrated to local time, then it is an easy matter to calculate our longitude from the difference between the two times. For example, if the difference between GMT and local time is three hours, then the difference in longitude must be 3 x 15 o.

Up until a majority of the world used Greenwich to set their clocks by. Although it did not influence the decision it seemed a fitting tribute to the hard work of John Flamstead and the Royal Observatory. One of these clocks can be seen today at the Observatory along with John Harrison's clocks. Scientific clocks were later used and the Observatory became a testing centre for new timepieces.

They would look at Flamstead House where a time-ball would drop at 1pm and then set their own chronometres by it. Later the railways and the electric telegraph would also use Greenwich Time. Time signals would be transmitted by telegraph in August using the new Shepherd electric clock.

Locale is the physical setting for relationships between people, such as the South of France or the Smoky Mountains. Finally, a sense of place is the emotions someone attaches to an area based on their experiences. Place can be applied at any scale and does not necessarily have to be fixed in either time or space.

Additionally, due to globalization, place can change over time as its physical setting and cultures are influenced by new ideas or technologies. Learn more about the physical and human characteristics of place with this curated resource collection.

Students look at lines of latitude and longitude on United States and world maps, discuss why these lines are helpful, and identify landmarks with similar latitude and longitude. The prime meridian is arbitrary, meaning it could be chosen to be anywhere. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.

Skip to content. Twitter Facebook Pinterest Google Classroom. Encyclopedic Entry Vocabulary. All lines of longitude are measured from the prime meridian.

Photograph by Bruce Dale. International Date Line. East of this line is one day earlier than west. Media Credits The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.

Media If a media asset is downloadable, a download button appears in the corner of the media viewer. Local Noon at your place is therefore exactly 1 hour 6 minutes or 1. This time difference corresponds to a longitude difference of 1. In your place, the Sun reached its maximum height before it did in Greenwich, that is, you must be East of Greenwich.