All About Clocks

All About Clocks 

The history of clocks is very long and there have been many different types of clocks over the centuries. Not all historians agree on the story of the clock. The word clock was first used in the 14th century (around 700 years ago). It comes from the word for bell in latin ( "clocca"). 

  

Using the Sun:

  

The first way that people could tell time by looking at the sun as it crossed the sky. As the sun was directly overhead in the sky, it was the middle of the day or on. As the sun was close to the horizon, it was either early morning (sunrise) or early evening (sunset). Tells the time was not very precise. 

  

Sundial clocks: 

  

The oldest type of clock is a sundial clock, also called a sun clock. They were first used around 3500 B.C. (about 5500 years ago). Sundial uses the sun to tell time. In the shadow of the sun points to a number on a circular disk that shows you the time. In the big picture below, right, so the shadow created by the sun points to 9, it is nine o'clock. 

  

Since Sundial depends on the sun, they can only be used to tell time during the day. 

  

Water clocks: 

  

Around 1400 B.C. (about 3400 years ago), water clocks were invented in Egypt. The name of a water-clock is clepsydra (pronounced suh-Klepper Druh). A water clock was made of two containers with water, one higher than the second. Water traveled from the higher container to the lower reservoir through a tube connecting the containers. The containers had marks showing the water level, and the marks told the time. 

  

Water clocks were very popular in Greece where they were improved many times over the years. Look at the picture below. Water drips from the higher container to the lower reservoir. As the water level rises in the lower reservoir, it raises the float on the surface of the water. The float is connected to a stick with notches and toxic over, turn the notches up a gear, moving the hand pointing at the time. 

  

Water clocks worked better than the sundial, because they said the time at night and during the day. They were also more accurate than the sundial. 

  

Parts year months and days:

  

The Greeks divided the year into twelve parts, called the month. They divided each month into thirty parts, called days. Their year had a total of 360 days, or 12 times 30 (12 x 30 = 360). As the earth goes around the sun in one year and follows a nearly circular orbit, the Greeks decided to divide the circle into 360 degrees. 

  

Divide the day into hours, minutes and seconds: 

  

Egyptians and Babylonians decided to divide the day from sunrise to sunset into twelve parts called hours. They have also divided the night, the time from sunset to sunrise, in twelve hours. But day and night is not the same length and the length of day and night also changes through the years. This system of measuring time was not very accurate because the length of one hour changed depending on the season. This meant that water clocks had to be adjusted every day. 

  

Someone finally figured out that by dividing the whole day in the 24 hours of the same length (12 hours per day plus 12 hours at night), so could be measured more accurately. 

  

Why was it night and day, divided into 12 parts? Twelve is about the number of lunar cycles in a year, so it is a special number in many cultures. 

  

The hour is divided into 60 minutes and each minute is divided into 60 seconds. The idea to divide the hours and minutes in 60 parts from the Sumerian sexagesimal system, based on the number 60: e of this system was developed around 4000 years ago. 

  

Pendulum Clocks: 

    

Before pendulum clocks were invented, Peter Henlein Germany invented a spring-driven clock around the 1510th It was not very precise. The first clock with a minute hand was invented by Jost Burgi in the 1577th It also had problems. The first practical clock was driven by a pendulum. It was developed by Christian Huygens around the 1656th By 1600, including the pendulum clock had a minute hand. 

  

The pendulum swings left and right, and when it swings, it becomes a wheel with teeth (see picture right). The turning wheel turns the hour and minute hands on the clock. On the first pendulum clocks, pendulum used to swing a lot (about 50 degrees). As pendulum clocks were improved, the pendulum swung very small (about 10 to 15 degrees). One problem with pendulum clocks is that they stopped running after a while and was rebooted. First pendulum clock with external batteries was developed around the 1840th In 1906, the batteries were inside the clock. 

  

As you already learned, a clock shows only 12 hours at a time, and the hands will go around the clock twice to measure 24 hours or a whole day. To tell the first 12 hours of the day (from midnight to noon), except the second 12 hours a day (from noon to midnight), we use these terms: 

AM - Ante meridiem, from the latin for "before noon" 

P.m. - Post meridiem, from the latin for "after dinner" 

  

Quartz Crystal Clocks:

  

Quartz is a type of crystal that looks like glass. When you are looking for excitement or electricity, and pressure, the quartz crystal vibrates or swings with a very constant frequency or speed. The vibrations move the clock hands very precisely. Quartz crystal clocks were invented in 1920. 

  

Time zones: 

  

Because the Earth rotates, the day in a part of the world when it is at night, on the other side of the world. In 1884, representatives from 25 countries and agreed to divide the world into time zones. If you draw a line around the center of the earth, it is a circle (the equator). The delegates divided the 360 degrees of the circle into 24 zones, each 15 degrees (24 x 15 = 360). They decided to start counting from Greenwich (pronounced GREN-ich), England, which is 0 degrees longitude. To see a bigger picture of standard time zones in the world, click on the picture below. 

  

In the continental U.S., there are four time zones: Eastern, Central, Mountain and Pacific. Each zone varies from one hour, so when it is 7 in the Eastern time zone, it's 6 in the central time zone, 5 in the Mountain Time Zone, and 4 in the Pacific Time Zone.