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Time

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Time Zones. Divisions of Earth with hourly displacements from GMT ... Some time zones will move an hour ahead or an hour back twice a year to allow ... – PowerPoint PPT presentation

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Title: Time


1
Time
  • Michelle Houck
  • April 28, 2008, 415pm EST

2
What is time?
  • Standard by which we measure
  • One of the fundamental units of physics
  • Broken into seconds, minutes, hours, days, weeks,
    months, years, decades, centuries, etc.

3
What is a second?
  • 1 second 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 caesium 133 atom

4
Mean Solar Time
  • We use the angle of the sun to tell time
  • 1 rotation of the Earth is one day, broken into
    24 hours
  • Abbreviated UT1

5
Greenwich Mean Time
  • Based at Royal Observatory, Greenwich, London
  • Mean solar time uses the angle of the sun to
    declare time, 1 rotation of the Earth 24 hours
  • Prime Meridian, all world times are based on this
    time
  • Locations east are hours and locations west are
    hours from GMT

6
Time Zones
  • Divisions of Earth with hourly displacements from
    GMT
  • Could divide the earth into 24 equally sized
    wedges, but political and geographical boundaries
    make some time zones irregular.

7
(No Transcript)
8
Daylight Savings Time
  • Some time zones will move an hour ahead or an
    hour back twice a year to allow for the hours of
    sunlight to be at the most convenient part of the
    day

9
Coordinated Universal Time
  • Abbreviated UTC
  • Very precise time standard kept using the average
    of 300 atomic clocks around the world

10
Leap Year and Leap Second
  • To adjust for slight differences in the solar
    time and standard time, we periodically add to
    our time.
  • Once every 4 years we add one day (February 29)
    to the year
  • When The difference between UTC and UT1 becomes
    greater than 0.6s, a leap second is announced,
    then either at the end of June or the end of
    December, one second is added between 235959
    and 000000 of the next day

11
How does my computer know what time it is?
  • The computer has an internal battery so it can
    keep track of time even when its turned off
  • If you have a continuous internet connection, the
    computer will automatically synchronize with an
    internet time server regularly
  • You can force the computer to synchronize with a
    time server
  • Can also set the computer to automatically adjust
    for daylight savings time, and other similar
    changes

12
What time is it?
  • http//www.time.gov/timezone.cgi?Eastern/d/-5/java
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