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Thread: How far away is the horizon??

  1. 28th December 2012, 12:44 PM #1
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    How far away is the horizon??

    We were talking the the volunteers at the double island point light house yesterday and he reckons the horizon was only 1km away....keep in mind this light house is probably >100m above sea level.....

    Soooo we are now sitting at sea level, well say 2m above sea level

    I reckon the horizon is 10km away.....
    Raggedy Ann reckons 4-5km away

    I wonder just how far off in the distance is really is

    Here is our view.....
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  2. 28th December 2012, 12:54 PM #2
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    It varies depending on your distance above sea level We generally work off around 20 mile or 32 kms but this is calculated on an average of 100m above sea level.
    The below link is a basic calculator.
    Distance to the Horizon Calculator
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  3. 28th December 2012, 12:58 PM #3
    sheerluck Guest
    Remembering that the earth is not a perfect sphere, but an oblate spheroid instead, the distance will alter slightly depending where you are on the earth's surface too.
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  4. 28th December 2012, 01:00 PM #4
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    Quote Originally Posted by CraigE View Post
    It varies depending on your distance above sea level We generally work off around 20 mile or 32 kms but this is calculated on an average of 100m above sea level.
    The below link is a basic calculator.
    Distance to the Horizon Calculator
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    As mentioned we are about 2m above sea level......so does mean its about 3.2k away??
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  5. 28th December 2012, 01:09 PM #5
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    According to the calculator its 5.1km bit more than the 1 they told you

    PS: Raggedy ann wins by a mile
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  6. 28th December 2012, 01:22 PM #6
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    At a course I did at school, they said a mirror reflection can be seen from aprox 25 miles away, not sure what that is in Klm's, but that was to the horizon.
    Does this mean I have to change my thinking?
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  7. 28th December 2012, 01:24 PM #7
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    Quote Originally Posted by THE BOOGER View Post
    According to the calculator its 5.1km bit more than the 1 they told you

    PS: Raggedy ann wins by a mile
    There's a calculator? We actually that somebody must have sorted a formula for working it out....
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  8. 28th December 2012, 01:29 PM #8
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    The volunteers at the lighthouse need a bit more training if they think the horizon is only a KM away. According to the calculator that CraigE posted, at 100 metres the horizon is 35.7 KM away...

    I was taught by my Scout leader that it was 10km away when standing up - looks like he was a bit out as well...
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  9. 28th December 2012, 01:33 PM #9
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    Craig posted a link to the cal in the 2nd post
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  10. 28th December 2012, 01:45 PM #10
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    Ignoring the effect of atmospheric refraction, distance to the horizon from an observer close to the Earth's surface is about

    d ≈ 3.57√h

    where d is in kilometres and h is height above ground level in metres.


    For an observer standing on the ground with h = 1.70 metres (average eye-level height), the horizon is at a distance of 4.7 kilometres.

    For an observer standing on a hill or tower of 100 metres in height, the horizon is at a distance of 39 kilometres.
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