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marino5856

Earth's Rotation - 0 views

www.polaris.iastate.edu/...unit3_sub1.htm

earth rotation 24 hours

shared by marino5856 on 07 Nov 14 - No Cached
  • The earth rotates about an imaginary line that passes through the North and South Poles of the planet.  This line is called the axis of rotation.  Earth rotates about this axis once each day (approximately 24 hours).  Although you most likely already knew that fact, there is a slight complication most people are not aware of.
  • More specifically, our rotation period (the time elapsed for one rotation) with respect to the stars  is called a sidereal day.  A sidereal day is 24 sidereal hours, or 23 hours and 56 minutes on a normal clock.  Our clock time is based on the earth's rotation with respect to the sun from solar noon to solar noon.  This is a solar day, and it is divided into 24 hours.  Because Earth travels about 1 / 365 of the way around the sun during one day, there is a small difference between solar time and sidereal time.
    • marino5856
      marino5856 on 07 Nov 14
       
      The earth rotates with axis lines and  there is 24 lines thats why there are 24 hours in a day. The earth time is rotated into 24hours because the earth rotate 1/365 during one day.
guzman5860

Why is the sky black at night? - 1 views

www.whyzz.com/why-is-the-sky-black-at-night

sky black

shared by guzman5860 on 31 Oct 14 - No Cached
  • As the Earth rotates it turns away from the sun’s light, and the sky becomes dark. However, if you think about the millions and millions of bright stars all around the sky at night, you might start to wonder why it isn’t just as bright as it was when we were facing the sun!
    • guzman5860
      guzman5860 on 04 Nov 14
       
      As the earth rotates it gets away from the sun and it starts getting dark and the moon comes out and the stars also but the moon and the stars don't give so much light. as the sun.
marino5856

Clocks - How Time Works - 1 views

science.howstuffworks.com/...time2.htm

How does the clock works

shared by marino5856 on 31 Oct 14 - No Cached
  • A day consists of two 12-hour periods, for a total of 24 hours. An hour consists of 60 minutes. A minute consists of 60 seconds. Seconds are subdivided on a decimal system into things like "hundredths of a second" or "millionths of a second."
    • marino5856
      marino5856 on 04 Nov 14
       
      There is 24 hours in a day because  they first divided 60 and that equals 12. So 12 plus 12 equals 24 so thats how they had 24 hours in a day.
  • hat's a pretty bizarre way to divide a day up. We divide it in half, then divide the halves by twelfths, then divide the twelfths into sixtieths, then divide by 60 again, and then convert to a decimal system for the smallest increments. It's no wonder children have trouble learning how to tell time.
  • How long is a day? It's the amount of time it takes for the Earth to rotate one time on its axis. But how long does it take the Earth to rotate? That is where things become completely arbitrary. The world has decided to standardize on the following increments:
  • ...3 more annotations...
  • Why are there 24 hours in a day? No one really knows. However, the tradition goes back a long way. Take, for example, this quote from Encyclopedia Britannica:
  • Why are there 60 minutes in an hour and 60 seconds in a minute? Again, it is unclear. It is known, however, that Egyptians once used a calendar that had 12 30-day months, giving them 360 days. This is believed to be the reason why we now divide circles into 360 degrees. Dividing 360 by 6 gives you 60, and 60 is also a base number in the Babylonian math system.
    • marino5856
      marino5856 on 04 Nov 14
       
      The Egyptians had a calendar that has 12 months so that equals 360 day in total. Also science they new that there is 360 days in a year thats why a circle is 360 degrees. The Roman people invented that so that in the clock there is not 24 hours in a clock so there is 12 am and 12pm.
  • What do a.m. and p.m. mean? These abbreviations stand for ante meridiem, before midday, and post meridiem, after midday, and they are a Roman invention. According to Daniel Boorstin in his book The Discoverers, this simple division of the day into two parts was the Romans' first increment of time within a day:
marino5856

hour (unit of time) -- Encyclopedia Britannica - 0 views

global.britannica.com/...hour

hours 24 not 60

shared by marino5856 on 31 Oct 14 - No Cached
  • in timekeeping
  • 3,600 seconds, now defined in terms of radiation emitted from atoms of the element cesium under specified conditions. The hour was formerly defined as the 24th part of a mean solar day—i.e., of the average period of rotation of the Earth relative to the Sun. The hour of sidereal time, 1/24 of the Earth’s rotation period relative to the stars, was about 10 seconds shorter than the hour of mean solar time.
    • marino5856
      marino5856 on 05 Nov 14
       
      It also has 24 hours the earth because in the system of the egyptians it said that it also has 24 hours because of the earth spinning.
  • In even earlier systems of timekeeping, an hour was 1/12 of a period of daylight or darkness—hence, variable in length with seasonal changes in the length of day and night. The custom of dividing the cycle of day and night into 24 periods seems to have originated with the ancient Egyptians.
marino5856

BrainPOP | Time Zones - 0 views

www.brainpop.com/...timezones

brainpop time zones

shared by marino5856 on 03 Nov 14 - No Cached
    • marino5856
      marino5856 on 07 Nov 14
       
      The earth is divided in 24 time zones. Time zones go north south pole  to north pole, they are meridians, They are 360 that are degrees. Thats why they are different times. They are the same minute but different hour to the west of it  and highest hour to the east. Smaller goes to west  and bigger to east. The earth rotates. Thats why the hour changes. Like the sun is up it has a different hour than when the moon is up. The earth soins 15 degrees per hour. The sun rises in L.A. at the same minute than N.Y. when it is getting dark.
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