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Increasing time of daylight

  1. Feb 10, 2012 #1
    what does this mean that every year the time of daylight in increasing on a specific date? is the speed of earth's rotation increasing or the speed of its revolution is increasing..plz help me out...
     
  2. jcsd
  3. Feb 10, 2012 #2
    Are you talking about the "daylight saving" programs?
     
  4. Feb 10, 2012 #3

    mathman

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    The main reason for seasonal variation of the time of daylight is the direction of the earth's axis relative to the sun. On Dec. 21 the north pole is tilted as far as possible away from the sun and on June 21 the north pole is pointed as close as possible toward the sun. Net result from Dec 21 to June 21 daylight increases in the northern hemisphere and decreases in the rest of the year. In the southern hemisphere the daylight variation is reversed.
     
  5. Feb 11, 2012 #4
    But can it be possible that the daylight will be of 23 hours and 9 minutes?
    if yes then what does it means?
    suppose on a given day after every year the time of daylight increase by 1 minute...then what does this mean?
     
  6. Feb 11, 2012 #5
    no i m not talking about them
     
  7. Feb 11, 2012 #6

    russ_watters

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    It doesn't - so what do you mean?
     
  8. Feb 11, 2012 #7

    sophiecentaur

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    Look at this animation and also google "day length and Earth tilt".
    Day length is a matter of what proportion of daily rotation gets sunlight on a particular place on the globe. If you're on the Pole, during the summer, there is sunlight all day and in winter it's dark all day. Nearer the equator, the light / dark is a pretty even split at all times.
    The Earth tilts the same way (in absolute terms) wherever it is around its yearly orbit - see the animation then figure it out.
     
  9. Feb 11, 2012 #8
    Then it is not true that the "the time of daylight in increasing on a specific date".
    The time of daylight increases and decreases continuously and periodically during the year.
    There is no specific date when is increasing. There are specific dates corresponding to the minima and maxima of the cycle (the solstices).
    Still not clear what are you talking about.
     
  10. Feb 11, 2012 #9

    sophiecentaur

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    It increases / decreases by a specific amount on every 'specific day'.
    I think we are just having a language / understanding problem.
     
  11. Feb 11, 2012 #10
    let me give the example of what m talking about..
    like on 21 December 92 AD the time of sunlight was 10 hours 18 minutes (used an online calculator)
    on 21 December 1800 AD the time of sunlight was 10 hours and 19 minutes...
    on 21 December 2800 AD the time of sunlight will be 10 hours and 20 minutes...
    through all these years the time is increasing by seconds and minutes and after some 1000 years it will increase by hours...
    i want to know that why is it happening?
    got it now?
     
  12. Feb 11, 2012 #11
    let me give the example of what m talking about..
    like on 21 December 92 AD the time of sunlight was 10 hours 18 minutes (used an online calculator)
    on 21 December 1800 AD the time of sunlight was 10 hours and 19 minutes...
    on 21 December 2800 AD the time of sunlight will be 10 hours and 20 minutes...
    through all these years the time is increasing by seconds and minutes and after some 1000 years it will increase by hours...
    i want to know that why is it happening?
    got it now?
     
  13. Feb 11, 2012 #12
    now got it?
     
  14. Feb 11, 2012 #13

    sophiecentaur

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    Did you not notice that it is DECREASING in the Autumn?
     
  15. Feb 11, 2012 #14
    whatever it does but on December 21 56994 the sunlight will be of 23 hours and 6 mins...
    what say about this?
     
  16. Feb 11, 2012 #15
    and not on the poles..it will be on equator
     
  17. Feb 11, 2012 #16

    sophiecentaur

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    Did you READ this or CALCULATE it? What info did you use?
     
  18. Feb 11, 2012 #17
    i calculated this...
    i used a tool..
    wolfram mathematica 8

    http://wolframalpha.com
     
  19. Feb 11, 2012 #18
    And what will be the length of the night on the same day?

    The explanation for your observation will depend on what that software is doing. I mean, first has to be established if this is a real fact or just something wrong in the software.
    Predicting the length of the day for long periods and taking into account all the perturbative factors is not an easy task. It may be just first order approximation, which works well for 100 years but breaks down for many thousands.

    Second, picking up a specific day (September 21) is not the best choice. The length of the day depends on how far from the solstice you are. The solstice does not "happen" always on September 21.
     
  20. Feb 11, 2012 #19
    i used 21 december because it has the shortest period of daylight...and wolframalpha is a software from creators of google...
    and yeah i believe that the first explanation might be right..
    but if it is correct then does it mean that the orbit of earth is increasing...or the sun is expanding or contracting?
     
  21. Feb 11, 2012 #20
    You mean Wolfram alpha has a built in function to calculate the length of the day?

    When I ask about the software I mean a specific application, based on some model. Not the computer program or computation environment used to run the application.
     
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