TIME, CALENDARS, AND SEASONS
Why did early humans have no need for hours, days, weeks, or months?
Because early humans were hunters and gatherers, they had little need to know exact time. What was essential was an understanding of the seasonal migration of animals and varieties of plant life.
What time is it at 12:00 a.m.?
12:00 a.m. is midnight. In the middle of the night, 11:59 p.m. is followed by 12:00 a.m., not 12:00 p.m., which is noon.
What do a.m. and p.m. mean?
The distinctions a.m. and p.m. are abbreviations for "ante meridiem" and "post meridiem," which mean before midday and after midday, respectively.
How does military time work?
Often known as military time, 24-hour time is used by many countries. It begins at midnight with 0000 and the day ends with 2359. The first two digits represent the hour and the last two digits represent the minutes. Since there are 24 hours in a day, each hour is numbered 00 through 23. For instance, 0100 is 1:00 a.m., 1200 is noon, 1300 is 1:00 p.m. , and 2043 is 8:43 p.m.
How long is a day?
A day is the time it takes the Earth to make one rotation, which is 23 hours, 56 minutes, and 4.2 seconds. We round this to an even 24 hours for convenience.
What's the difference between Greenwich Mean Time, Universal Coordinated Time, and Zulu Time?
Greenwich Mean Time (GMT), Universal Coordinated Time (UTC), and Zulu Time are three different names for the same time zone. This time zone is situated at the Prime Meridian, zero degrees longitude, and runs through the Royal Observatory at Greenwich, a section of London, England. It is the Prime Meridian from which other longitudes are determined, east and west.
Does the Earth always rotate and revolve around the sun at the same speed?
No, the Earth's revolution around the sun and rotation on its axis are not perfect. Its daily rotation may vary by approximately four to five milliseconds, and is slowing down at a rate of one millisecond each century, due to tidal friction. Additionally, the axis wobbles slightly, and the length of revolution around the sun varies by a few milliseconds.
How can I find the exact time?
Today, you can go to many Web sites on the Internet and find the exact time. Just search the word "time," and you will see links for the exact time. Your computer also is set to automatically update time, so your desktop time is usually accurate to within a few milliseconds.
When were time zones established in the United States?
In 1878, Sir Sanford Fleming proposed dividing the world into 24 time zones, each spaced 15 degrees of longitude apart. The contiguous United States was covered by four time zones. By 1895, most states had begun to institute the standard time zones of Eastern, Central, Mountain, and Pacific on their own. But it wasn't until 1918 that Congress passed the Standard Time Act, establishing official time zones in the United States.
How did trains help establish time zones?
Before trains, many cities and regions had their own local time, which was set based on the sun at their location. The great variation of local times made train schedules confusing. In November 1883, railroad companies across the United States and Canada began to use standard time zones—years before they came into general use across the United States.
Most—but not all—countries around the world are divided into one-hour time zones (U.S. Central Intelligence Agency, The World Factbook 2008).
How many time zones does the United States have?
The United States spans nine time zones: Eastern, Central, Mountain, pacific, Alaska, Hawaii-Aleutian, Samoa, Wake Island, and Guam.
Which states are split into multiple time zones?
Florida, Indiana, Kentucky, and Tennessee are split into Eastern and Central time. Kansas, Nebraska, North Dakota, South Dakota, and Texas are split between Central and Mountain time. Idaho and Oregon are split between Mountain and Pacific time.
Are all countries divided into one-hour time zones?
No. China and some other countries do not divide their territory by time zones at all. Several countries use half-hour time zones, including Afghanistan, Australia, Burma, India, Iran, the Marquesas, and Venezuela; also, the Canadian province of Newfoundland uses half-hour zones. Quarter-hour divisions are used in Nepal, as well as in some provinces, including the Chatham Islands.
How many time zones does China have?
Since China is such a large country, it should span five time zones, but the entire country uses one time—eight hours ahead of UTC.
Why did the International Date Line recently move?
Prior to 1995, the country of Kiribati, consisting of 21 inhabited islands, straddled the International Date Line, thus dividing the country into two days. In 1995 Kiribati decided to shift its portion of the International Date Line far to the east so that the entire country could be on the same side of the Date Line.
What time is it at the North and South Poles?
Because time zones get narrower the farther you get from the equator, time zones would be very thin near the North and South Poles. To simplify things, researchers living in Antarctica use Coordinated Universal Time (UTC), which is the time at Greenwich, England.
What happens when I cross the International Date Line?
If you fly, sail, or swim across the International Date Line from east to west, such as from the United States to Japan, you add a day (Sunday becomes Monday). When you travel from west to east, such as from Japan to the United States, you subtract a day (Sunday becomes Saturday).
How fast do you have to travel west to arrive earlier than when you left?
Normally, when flying between London and New York, the trip takes seven hours. Thus, with the five-hour difference in time between the two cities, you arrive two hours "later" than when you left London. If you could have flown on the now decommissioned Concorde, which traveled at Mach 2 (1,300 miles [2,092 kilometers] per hour— two times the speed of sound), the trip between London and New York would have taken only three hours. Thus, with the five-hour difference in time zones, you would have arrived two hours "earlier" than when you left!
Why is Russia always one hour ahead?
In an effort to take advantage of the limited amount of light available in winter months, each of Russia's time zones are one hour ahead of the standard time for those zones. Russia also follows Daylight Saving Time and adds an additional hour during spring and summer months.
When was Daylight Saving Time instituted?
Though Benjamin Franklin suggested the concept of Daylight Saving Time in 1784, it was not implemented in the United States until World War I. Between World Wars I and II, states and communities were allowed to choose whether or not to observe the change. During World War II, Franklin Roosevelt again implemented Daylight Saving Time. Finally, in 1966, Congress passed the Uniform Time Act, which standardized the length of the Daylight Saving Time period. But states and territories can choose not to observe Daylight Saving Time. Arizona, Hawaii, parts of Indiana, Puerto Rico, and some island territories have chosen not to observe Daylight Saving Time.