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Re: True North - Sorry - 1 hour error in original calc.



Hi David,
    I will try to explain this more clearly and correctly.

    The thing I was looking for was solar noon (12:00).
Solar noon at Greenwich (0 degrees of longitute) is at 12:00 UTC or as it
used to be known GMT (Greenwich Mean Time). (Greenwich is a place in London
where the British Navy, centuaries ago decided was the place that
longititude should be measured from and so they went to considerable expense
(British Board of Longitude) setting up observatories at may places arrouund
the world which they used to determine the longitude of that location. Since
clocks several centuaries ago did not keep time all that accurately, they
used astronomical events to claibrate their measurements. Australia (the
east coast) was discovered by Captain James Cook and his crew in 1770. They
were sent on a mission by the British Board of Longitude to observe the
transit of the planet Venus across the Sun from the islands of Taheti and
the position of the sun in the sky in order to accurately determine the
longitude of Taheti. The transit of Venus could be accurately calculated and
so time in Greenwich and Taheti could be accurately calculated and therefor
the longitude difference.

    We now have accurate clocks and we can usually find out our longitude
and so calulating solar noon is not so difficult.

    As I previously said, the thing we are looking for is solar noon as this
will directly give us the direction of North or South. We know solar noon at
Greenwich is 12:00 UTC. For my longitude which is 151.06278 Degrees. The
Earth rotates once (360 Degrees - actually almost 361 as the Earth moves
almost 1 degree around the Sun each day but we are interested in angles with
respect to the position of the Sun, not the rest of the Universe) in 24
hours and so that is 15 degrees per hour (360/24=15). My home is
151.06278/15 = 10.070852 Hours ahead of UTC. Therefore my solar noon will
occur 10.070852 Hours before 12:00 UTC and so that is 12.000000 - 10.070852
= 1.929148 or 01:55 and 45 seconds. [In my previous email there is a 1 hour
error - I forgot that I have Daylight savings operating here - clocks put
forward 1 hour during summer - dumb idea - I think it would be good for the
whole world to set clocks to UTC!]

Regards,
Murray Peterson
VK2KGM

----- Original Message -----
From: "David Tan" <david@dht.pc.my>
To: <vk2kgm@ihug.com.au>
Sent: Thursday, February 08, 2001 2:43 AM
Subject: Re: True North


>
>
> Hi Murray,
>
> I have read and very interest your article about True North which
> posted in [amsat-bb], but sorry, I still can't understand the
> following example you wrote:
>
> >Expressed as a decimal that is 151.06278 Degrees. The Earth rotates once
> >(360 Degrees) in 24 hours and so that is 15 degrees per hour. So my QTH
is
> >151.06278/15 Hours ahead of UTC or GMT. Solar noon for me is at  0255
(should be 0155)
> >and 45 seconds UTC.
>
> How to convert the  151.06278/15 Hours ahead of UTC to 0255 and 45
> seconds UTC,. Your further explaination would very much appreciate.
>
> I also visited your website, it was very interesting.
>
> 73 ..  David, 9M2DT
>
>
>
>
>

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