Metrology-4-Time Flashcards
Explain the Time Calender part 1
In Babylonia, again in Iraq, a year of 12 alternating 29-day and 30-day lunar
months was observed before 2000 B.C., giving a 354-day year.
What did the Mayans of Central America rely on to establish 260 and 365 day calenders?
The sun, moon and planet Venus
When did the Mayan culture flourish from and what did this indicate about their beliefs?
Flourished from around 2000 B.C. until about 1500 A.D. They left celestial-cycle records indicating their belief that the creation of the world occurred in 3113 B.C.
Their calendars later became portions of the great Aztec calendar stones.
What type of calendar has other civilisations like our own adopted?
A 365-day solar calendar with a leap year occurring every fourth year.
When and who initiated clock-making as opposed to calendar-making?
5000 to 6000 years ago great civilisations in the Middle East and North Africa.
When and what was the first portable timepiece to measure the passage of hour come into use?
1500 B.C, Egyptian shadow clock or sundial.
This device divided a sunlit day into 10 parts plus two twilight hours in the morning and evening.
What are the two basic components that clocks must have?
- A regular, constant or repetitive process or action to mark off equal increments of time. early examples include movement of sun, sand in glass( hour glass) oil lamps.
- A means of keeping track of the increments of the time and displaying the result.
Our means of keeping track of time passage include the position of the clock hands and a digital time display.
Who made the first pendulum clock?
Dutch scientist, Christiaan Huygens.
What was the first pendulum clock regulated by?
A mechanism with a natural period of oscillation
What was the error of Huygens’ pendulum clock?
Less than 1 minute a day, his later refinements reduced his clock’s error to less than 10 seconds a day.
When and who improved the pendulum clock’s accuracy to 1 second a day?
1721, George Graham
How did George Graham improve the pendulum clock’s accuracy?
He compensated for the changes in the pendulum’s length due to temperature variations.
Who refined and added new methods of reducing friction to the pendulum clock?
John Harrison
What did john Harrison do by 1761?
He built a marine chronometer with a spring and balance wheel escapement that won the British government’s 1714 prize offered for a means of determining longitude to within one-half degree after a voyage to the West Indies.
What did the marine chronometer do on on board a ship?
It kept time on a rolling ship to about one-fifth of a second a day, 10x better than required.
When and who developed a clock with a nearly free pendulum which attained an accuracy of a hundredth of a second a day.
1889, Siegmund Riefler
When was the standard of time changed to quartz crystals?
1930s and 1940s
This improved time keeping performances far beyond that of pendulum and balance-wheel escapements.
What is Quartz clock operation based on?
Piezoelectric property of quarts crystals
Explain the piezoelectric property of quartz crystals?
If you apply an electric field to the crystal, it changes its shape, and if you squeeze it or bend it, it generates and electric field.
