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*Subject*: [amsat-bb] Re: True North - Sorry - 1 hour error in original calc.*From*: "Murray Peterson VK2KGM" <vk2kgm@xxxxxxxxxxx>*Date*: Thu, 8 Feb 2001 09:09:42 +1100

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 > > > > > ---- Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA. To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org

**Follow-Ups**:**Re: Re: True North - Sorry - 1 hour error in originalcalc.***From:*Rick Walter

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