Time & Calendars

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As of 2014, the number of work days per year in the United States varies between 260 and 262. A major reason for the variation is leap year, which can lead to an extra work day in a given year. Holidays also play a role in the variation.

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  • Who invented the first calendar?

    Q: Who invented the first calendar?

    A: Evidence indicates that the first calendar was created by the Stone Age people in Britain about 10,000 years ago. The earliest known calendar was a lunar calendar, which tracked the cycles of the moon.
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  • What is the Mesozoic era?

    Q: What is the Mesozoic era?

    A: The Mesozoic Era is commonly referred to as "the age of the dinosaurs" because it was the time period when dinosaurs dominated the earth. The Mesozoic Era lasted for approximately 180 million years, from around 251 to 65 million years ago.
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  • How many days are in summer?

    Q: How many days are in summer?

    A: In the Northern Hemisphere, the official summer season begins with the June solstice, which takes place on June 20th, 21st or 22nd each year, and ends with the September equinox, which takes place on September 22nd or 23rd each year; the exact duration of summer depends on when the solstice and equinox will take place and can range from 92 to 95 days. Though summer is associated with warm temperatures and the concept of 'summer break' for students, the season has an official scientific definition, as is defined above. Summer weather in the Northern Hemisphere may begin before the official start of the season and last until after fall has begun with the advent of the September equinox.
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  • How do we measure the length of one second?

    Q: How do we measure the length of one second?

    A: The simple second has a complex origin: it is measured as "the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom," according to the National Institute of Standards and Technology. This highly technical definition was introduced in 1967 at a meeting of the General Conference on Weights and Measures (CGPM), an international organization.
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  • How did the Ancient Egyptian calendar work?

    Q: How did the Ancient Egyptian calendar work?

    A: Ancient Egypt refers to a long period of time in history, but there is evidence that Egyptian society once used a lunar calendar before switching to a solar 365-day calendar. They eventually used the stars to predict important agricultural events like the flooding of the Nile River. Their older lunar calendar did not take the Nile flood into account, and it was eventually replaced by one that helped predict the river's flooding.
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  • What happens in spring?

    Q: What happens in spring?

    A: During spring, the axis of the Earth starts to tilt toward the sun, which causes the hours of daylight to increase in countries located in the Northern Hemisphere. Air, water and ground temperatures also increase, leading to growth of new plants. The animals that consume the newly regenerating plants begin to appear, followed by their predators.
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  • What happens to the Chinese calendar in 2033?

    Q: What happens to the Chinese calendar in 2033?

    A: Chinese astronomers made an unusual discovery in the 1990s when it was found that the traditional Chinese calendar has an erroneous or "fake" leap month in the year 2033. This traditional calendar works such that its calculations are balanced out by the addition of an entire leap month rather than a single leap day.
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  • What is the oldest calendar still being used today?

    Q: What is the oldest calendar still being used today?

    A: According to the Guinness World Records organization, the Jewish Calendar, which has been in use since the 9th century C.E., is the oldest calendar still in popular use. This calendar is used to determine the dates of Jewish holidays such as Rosh Hashanah and Yom Kippur.
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  • What hours are considered evening?

    Q: What hours are considered evening?

    A: The evening is generally understood to encompass the hours from before sunset to just after nightfall or bedtime, a period of time that ranges from roughly 4 p.m. to 10 p.m. In general, the term "evening" is used to describe a vague period of time that is somewhere between the afternoon and night.
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  • What happens after the end of the Mayan calendar?

    Q: What happens after the end of the Mayan calendar?

    A: Though a popular misconception held that the Mayan calendar ended with the destruction of everything in existence, the end of the calendar was simply the end of an era, after which the calendar would reset. Some people believed that the Mayan calendar, which ended on a date that coincided with December 21, 2012, predicted the end of the world, but this is not the case.
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  • Has the New Year always been January 1?

    Q: Has the New Year always been January 1?

    A: January 1 was not always the date of the first day of a new calendar year, and at a certain point in time, the month of January did not even exist. Even today, cultures that use different calendars than the standard Gregorian calendar have New Year celebrations on days other than January 1, though in most places, January 1 is the official start of a new year.
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  • How do the seasons happen?

    Q: How do the seasons happen?

    A: The seasons occur because of Earth's tilt on its axis. The axial tilt of 23.5 degrees from the vertical axis influences how much sunlight the northern and southern hemispheres receive relative to one another. This in turn determines the length of day and night, average temperature and other aspects of climate.
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  • Why are there 24 hours in a day?

    Q: Why are there 24 hours in a day?

    A: At first glance, some may find the 24 hour number confusing or even arbitrary given that most other major measures of time, including seconds and minutes, are defined by 60 units. But the division of the day into 24 equal parts goes back to Ancient Egypt, which used stars as a way of dividing up the time in a day.
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  • How does the Chinese calendar count years?

    Q: How does the Chinese calendar count years?

    A: Unlike the Gregorian calendar, which counts years infinitely, the traditional Chinese calendar is lunisolar and rotates on a 60-year cycle. This means that the years on a Chinese calendar don't ascend in chronological order, and instead its years are named with words rather than numbers. The year names are based on a combination of one of 10 prefixes, or stems, and one of 12 suffixes, or branches.
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  • What day do we turn the clocks back?

    Q: What day do we turn the clocks back?

    A: The date that clocks are turned back for Daylight Savings Time changes each year. In 2015, the day to turn the clocks back is Nov. 1. The day to turn the clocks forward an hour is be March 8, 2015.
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  • On what day does fall start?

    Q: On what day does fall start?

    A: Among astronomers, the general consensus for the start of the fall season is when the sun's central disk traverses the celestial equator in a southward direction, normally occurring around the third week of September. However, meteorologists mark the beginning of autumn on September 1.
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  • How do you change GMT to EDT?

    Q: How do you change GMT to EDT?

    A: GMT is commonly known as Greenwich Mean Time. It is considered the world standard time. It is also referred to as "UTC," or Coordinated Universal Time. Conversion of a time listed in GMT to Eastern Daylight Time is a matter of subtraction.
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  • What months make up the first quarter?

    Q: What months make up the first quarter?

    A: January, February and March are the months that make up the first quarter if an organization's fiscal year starts at the beginning of January. Different organizations may start their fiscal years at different times, though, and the first three months of that time period would make up the first quarter. In the business and government sectors in the United States, a year is divided up into four pieces, each of which is called a quarter. This is done so that analysts, accountants, independent contractors, investors, tax regulators and other interested parties can easily track growth, profits, goals and set due dates for certain regulatory items.
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  • How many work weeks are in a year?

    Q: How many work weeks are in a year?

    A: There are 52 recognized work weeks in a year. This is based on a regular calendar year in the United States where employees work a 40-hour work week.
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  • What is considered a calendar day?

    Q: What is considered a calendar day?

    A: A calendar day is a period from midnight on a given day to midnight on the next day. Thus, a calendar day is a period of 24 hours starting from midnight.
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  • How many workdays are there in a year?

    Q: How many workdays are there in a year?

    A: As of 2014, the number of work days per year in the United States varies between 260 and 262. A major reason for the variation is leap year, which can lead to an extra work day in a given year. Holidays also play a role in the variation.
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