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Calculating latitude and longitude at any time

  1. Jun 30, 2014 #1
    Calculating latitude at noon is easy: say I got ##73^o## on 6/20/2014
    So, ##90^o-73^o=17^o##
    then ##17^o+(\frac{1}{91})^o=17.01^o##(i forgot how to find N or S:biggrin:
    Calculating longitude is also easy: First I set my watch to 12 00 at solar noon.
    Then, I find the time difference between my watch and GMT--- say, 5h 37m 12s ahead
    Since one hour is equal to 15o(##\frac{360}{24}##),
    then: ##(5+\frac{37}{60}+\frac{12}{3600})hours*15 \frac{degrees}{hours}=84.3^oE##
    ............I know it is possible to do this any time, but how?:confused:
    I suppose it is a totally different method. Does anyone know how to do this?

    For example, I got: 46o/SUP] at 15 39, PST(Pacific Standard Time) on April 24th, 2016. How do I calculate latitude?

    And how do I do longitude? Do I find the difference in celestial longitude(RA or Dec i forgot:redface:) , divide by 15 to find the time since solar noon and set my watch to 12 00 + difference? (perhaps it'll work....... who knows!:tongue2:)
    Last edited: Jun 30, 2014
  2. jcsd
  3. Jun 30, 2014 #2
    oops... please move this to 'Other sciences>>Earth'

    Buhowyeesii ;)
    Last edited: Jun 30, 2014
  4. Jun 30, 2014 #3

    I asked a sailor the other day. He said, shoot three stars at specific times and then look up the result in a book of tables. Surely there is more detail available out there under the heading of navigation.
  5. Jul 1, 2014 #4
    Well, I already know this way. What I meant is in the daytime and using the sun, chronograph and other things like that.
  6. Jul 1, 2014 #5
    The exact way to do it is like this.
    1. Find three or more brighter(and therfore more important) stars.
    2. Measure the height of each star in at most two minutes with a sextant or something. Two minutes would give you plenty of time to measure and also, the amount of error is not so high.
    3. Find the geographic positions(lat. and long. on earth where the star appears overhead) of each star and mark those coordinates on a double map. (two identical maps joined together)
    4. Draw a circle around each of the points with their radii according to the heights observed for each star.
    5. The place where all the circles intersect is the approximate location of your ship.
  7. Jul 1, 2014 #6
  8. Jul 2, 2014 #7


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    It's PF policy not to allow the same thread topic to be posted to multiple forums.

    If you are interested in how to navigate and determine your position, read this article first:


    If, after reading the article above, you want all the gory details about the tools used in navigation, you can read the book "American Practical Navigator", which can be downloaded from this site (relax, Mentors, it is a government publication):


    The whole book is 35 Mbytes, but you can download only the chapters of interest.

    Nowadays, chronometers, sextants, almanacs, astrolabes, and all the other traditional navigational paraphernalia have been largely superseded by the Global Positioning System (GPS):


    You can purchase a relatively inexpensive GPS receiver which can be used to tell your lat/long. position to within a few meters of your actual location. The better receivers can also determine your altitude w.r.t. sea level and speed.
  9. Jul 3, 2014 #8
    Calculating latitude by the solar angle/time of day must take into account the date or it will not be accurate.
    GPS does provide great accuracy, but to rely on technology (and battery life for that matter) without self reliance as a back up plan is foolish, at least on blue water (IMNSHO).
  10. Jul 12, 2014 #9
    I just do not like GPSs. They give you your exact location, BUT to me I feel like a dummy, using that.
    What I asked for was one that you could use your brain on.

    I need to find lat. and long. at any time of a given day.
  11. Jul 12, 2014 #10
    Yes, I quite agree. :biggrin:
  12. Jul 12, 2014 #11


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    Then I humbly suggest you download and start studying the American Practical Navigator and rounding up the required instruments.

    The other systems for marine navigation, like LORAN-C or DECCA, have been decommissioned. Like it or not, GPS is used by the military to locate targets and navigate land vehicles, aircraft, and ships. It has superseded inertial navigation systems in the guidance of cruise missiles and ICBMs. You want to drop a bomb down a smokestack, it's gonna have a GPS receiver attached to it. You want to go hiking in the woods, carry a GPS receiver.

    And other countries are jumping on the band-wagon with competing systems. The Russians and Chinese have their own satellite-based systems similar to GPS, largely for military use, and the EU is reportedly planning on building its own satellite navigation system as well.
  13. Jul 30, 2014 #12
    I was not so extreme as to that though... I will have a look at the book.:smile:
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