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Homework Help: Standard and solar time

  1. Sep 14, 2012 #1
    1. The problem statement, all variables and given/known data

    Consider the following: city: Córdoba, Argentina
    Longitude = 64 deg 10 min W
    Latitude = 31 deg 28 min S
    Time zone = GMT -3
    Date = 01 August
    On this date, the equation of time = -6 minutes. Assume no daylight saving time

    (a) Determine the standard time at solar noon.
    (b) Determine the hour angle at 8 AM standard time.

    2. Relevant equations
    earth rotates 15degrees per hour

    3. The attempt at a solution
    15(3) = 45
    64.1667 - 45 = 19.1667degrees.
    if earth rotates at 15Degrees per hour then that means for 19.1667degrees it needs to rotate about 1hour 17minutes.

    thus standard time at solar noon is 12.00 - 1hour and 17 minutes + 6minutes
    = 11.49am

    is that right so far?

    using above answer, for part b i did the following:

    from 8am to 11.49am there is 3hours 49 min difference.

    (3 + 49/60) * 15 = 57.25degrees.

    is that right?
    Last edited: Sep 14, 2012
  2. jcsd
  3. Sep 14, 2012 #2
    In your attempt at a solution in the first part, your method is fine, but there is a very simple arithmetic slip in your working.

    Your calculation for the second part seems fairly right, except that the mistake in the first part has carried through. Do you know the sign convention for hour angle? Remember that the sun travels anti-clockwise around the sky in the Southern hemisphere. Does that make a difference? Or does the fact that it still travels from East to West make a calculation the same as in the Northern hemisphere? You do need to think carefully about that aspect before you hand your work in.
  4. Sep 14, 2012 #3
    No I'm not familiar with the sign convention.

    for the first part should it be 12.00 + 1hour and 17 minutes + 6minutes= 1.23pm??
  5. Sep 14, 2012 #4
    check the sign convention by google hour angle

    for the first part no, that is not the slip -- you have said that standard time is an hour and a bit before noon -- does that match the time you have arrived at?
  6. Sep 14, 2012 #5
    Im not sure what you mean by what time I arrived at.
  7. Sep 14, 2012 #6
    is 11.49 an hour and a bit before noon?
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