Time is determined by several factors. First, the earth’s position as it rotates on its axis is one factor as to when it is light (day) and when it is dark (night). When a location is facing the sun, it is day and when it is not facing the sun, it is night. Thus, when it is daytime in the United States, it is nighttime in Asia.

The other factor is the time zone of the place which is determined by its longitude. This is how far a east or west a place is from the Prime Meridian, which is located in Greenwich, England.

The precise time is determined by what time zone you live in. For example, people who live on the east coast of the United States live in the Eastern Time Zone while those on the Pacific Coast live in the Pacific Time Zone. Due to the fact that the earth rotates and different view of the same location face the sun, the time is different depending at which point the earth is facing as it rotates, with western time zones having later times than eastern.

The United States is divided into four times zones: the Eastern, Central, Mountain and Pacific time zones. If it is nine o’clock in New York (Eastern Standard Time), it would be six o’clock or three hours earlier in Los Angeles, which is in the Pacific Standard Time zone. These are the time zones for the main land United States – there are two more for the states of Alaska and Hawaii.

### Time Zones of the United States

EST = Eastern Standard Time

CST = Central Standard Time
MST = Mountain Standard Time
PST = Pacific Standard Time

## The Revolution of the Earth Around the Sun

Another aspect of the earth’s time frame is the revolution of the earth around the sun. This causes the changes in the seasons and marks a new year on the calendar.

The earth, while rotating on its axis, also revolves around the sun, as well as the other planets. Each time the earth revolves around the sun, another year passes. This means that it makes a circle around the sun. This circle is called an orbit. It takes the earth 365 days or one year to complete this circle or orbit around the sun.

The earth also tilts as it rotates around the sun. On June 21st, the North Pole is tilting towards the sun. This means that the northern hemisphere or northern half of the earth is getting more direct rays from the sun. This is the time that summer begins in the northern hemisphere.

Meanwhile the southern hemisphere is not getting direct rays from the sun. In the southern hemisphere, they are experiencing winter when we are having summer because they are not getting the sun’s direct rays. Likewise, on December 21st when it is the beginning of winter in the northern hemisphere, it is summer in the southern hemisphere because the earth is tilted towards the southern hemisphere.

On March 21st and September 23rd, the beginning of spring and fall, the earth is not tilted more towards the North Pole or the South Pole. Thus the weather in both hemispheres is more alike.

Below is an illustration of revolution. In reality, the sun is much, much bigger in size than the earth and the other planets are revolving around the sun as well.