Guiding Question:
Can you determine the correct time as we travel around the world?
Mastery of the Lesson:
- Pass time zone quiz at 80% mastery
- Correctly explain how international timezones work during student/teacher conference & Voki virtual assignment
Correctly label time zones after guided practice
Best Practices Used:
Buddy Check - will determine if lesson has been clear and successful; students use higher order questions to check for understanding
Closure: a Ticket Out of the Door will determine student's awareness of objective's relationship to real world experiences.
(All learning styles have been addressed and were differentiated in this lesson: visual, auditory & kinesthetic)
VOCABULARY:
- Horology - the science of measuring time; an horologist is a scientist who studies the measurement of time.
- Earth's rotation - the earth rotates 1 complete time in 24 hours
- meridians (longitude lines) - the ancient Greeks mathematically divided the earth into 360 equal segments that were 15° wide in order to create a system of time for each 24 hour day
- 360 ÷ 24 (hours) = 15 (or 15°)
- Prime Meridian - 0° longitude (the starting point)
- Greenwich Mean Time (GMT) - Greenwich, England is the city that sits directly on the Prime Meridian; GMT refers to solar time at the Royal Observatory in Greenwich, England. Also referred to as Zulu Time.
- International Dateline - a generally north-south imaginary line on the surface of the Earth, passing through the middle of the Pacific Ocean, that designates the place where each calendar day begins. It is roughly along 180° longitude, opposite the Prime Meridian.
A Brief History of Time
Before the 19th Century
Many cities around the world historically kept their own time by using some type of instrument to observe the sun’s zenith at noon. The earliest time measuring devices used either the sun’s shadow or the rate in which water runs out of a vessel. The pendulum clock was developed during the 17th century – these clocks were sufficiently accurate to be used at sea to determine longitude and for scientific time measurement in the 18th century.
English horologist John Harrison proved in 1764 that a clock could be used to locate a ship's position at sea with extraordinary accuracy. A new Longitude Act, known as the Act 5 George III, followed in 1765. Chronometers, which measure time accurately in spite of motion or varying conditions, became popular instruments among many merchant mariners during the 19th century.
Still, even after developments regarding longitude, many towns and cities set clocks based on sunsets and sunrises. Dawn and dusk occur at different times but time differences between distant locations were barely noticeable prior to the 19th century because of long travel times and the (lack of) long-distance communications. The use of local solar time became increasingly awkward as railways and telecommunications improved. Time zones were therefore a compromise, relaxing the complex geographic dependence while still allowing local time to be approximate with mean solar time.
The Call for One Prime Meridian
Various meridians were used for longitudinal references among different countries prior to the late 1800s. However, the Greenwich Meridian was the most popular of these. The Greenwich Observatory's reputation for the reliability and accuracy in publications of its navigational data was one factor that contributed to the Greenwich Meridian’s popularity. Moreover, the shipping industry would benefit from having just one prime meridian. Many people informally recognized the Greenwich Meridian as the prime meridian prior to the International Meridian Conference in 1884.
Sir Sandford Fleming was one of the key players in developing a satisfactory worldwide system of keeping time, according to sources such as the Canadian Encyclopedia. He advocated the adoption of a standard or mean time and hourly variations from that in accordance with established time zones. He also helped convene the International Meridian Conference in 1884, where the international standard time system was adopted.
The International Meridian Conference
The International Meridian Conference at Washington DC, USA, adopted a proposal in October 1884. The proposal stated that the prime meridian for longitude and timekeeping should be one that passes through the center of the transit instrument at the Greenwich Observatory in the United Kingdom (UK). The conference therefore established the Greenwich Meridian as the prime meridian and Greenwich Mean Time (GMT) as the world’s time standard. The international 24-hour time-zone system grew from this, in which all zones referred back to GMT on the prime meridian.
The main factors that favored Greenwich as the site of the prime meridian were:
- Britain had more shipping and ships using the Greenwich Meridian than the rest of the world put together (at the time). The British Nautical Almanac started these charts in 1767.
- The Greenwich Observatory produced data of the highest quality for a long time.
Time Zones in the 20th Century
Interestingly, many French maps showed zero degrees at Paris for many years despite the International Meridian Conference’s outcomes in 1884. GMT was the universal reference standard – all other times being stated as so many hours ahead or behind it – but the French continued to treat Paris as the prime meridian until 1911. Even so, the French defined legal time as Paris Mean Time minus nine minutes and 21 seconds. In other words, this was the same time as GMT. France did not formally use to Coordinated Universal Time (UTC) as a reference to its standard time zone (UTC+1) until August in 1978 (Sheen, cited in Brannel Astronomy, n.d.).Standard time, in terms of time zones, was not established in United States law until the Act of March 19, 1918, sometimes called the Standard Time Act. The act also established daylight saving time in the nation. Daylight saving time was repealed in 1919, but standard time in time zones remained in law, with the Interstate Commerce Commission (ICC) having the authority over time zone boundaries.
Many countries adopted hourly time zones by the late 1920s. Many nations today use standard time zones but some places adopt half-hour deviations from standard time or use quarter hour deviations. Moreover, countries such as China use a single time zone even though their territory extends beyond the 15 degrees of longitude.
A brief history of time zones. (October1, 2011). Retrieved from http://www.timeanddate.com/time/time-zones-history.html
