NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar longitudes, not by lunar distance. Was- Re: Working a lunar
From: Brad Morris
Date: 2009 Aug 7, 12:23 -0400
From: Brad Morris
Date: 2009 Aug 7, 12:23 -0400
Hang on George, Hanno has required that the moon and the other object be ON the meridian at different times, and that the delta time between those meridian passages be the key component. I agree with your statement that it is the same for everybody on earth, should that delta time not include the meridian passage. Once the meridian passage is included however, then only ONE meridian has that precise delta time, the meridian of observation. As the earth rotates and the moon changes position, then the delta time will change. At your meridian in the UK, the delta time will be X. By the time those same objects individually CROSS MY MERIDIAN in the US, about 5 hours later, the position of the moon will change by about 2.5 degrees. Thus the delta time between those objects on my meridian will be different! Anyone on your meridian, independent of latitude and under the assumption that they can see them, will get the same delta time. Best Regards Brad -----Original Message----- From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of George Huxtable Sent: Friday, August 07, 2009 11:07 AM To: NavList@fer3.com Subject: [NavList 9402] Lunar longitudes, not by lunar distance. Was- [NavList 9393] Re: Working a lunar Hanno Ix wrote, in 9382, If I see things right, there must be a LOP which connects all locations on Earth with a given, fixed difference DT between the meridian passages of sun and moon. What I meant is: If I see things right, there must be a LOP which connects all those locations on Earth that have a given, fixed difference DT between the meridian passages of sun and moon. ================ Is there woolly thinking here, I wonder? Wherever on Earth the Moon is seen from, it's phase is the same except for the effects of parallax, which can be corrected for. At Full Moon, it's always very nearly 180 � from the Sun. So that's the Sun's lunar distance, which is the same wherever on Earth it's observed from. And then the time difference between meridian passages of Sun and Moon is 12 hours, the whole World over. The phase of the Moon, the lunar distance, and the time difference between meridian passages, change in step, going through a whole cycle in a month, and at any moment in the month all are the same wherever on Earth they are observed from. Measuring a lunar distance, or the time between meridian passage (or even the phase, if it was possible to do that precisely), all provide the same message: the time of the month. From that time of the month, from the nautical tables, we could deduce the day (if that was needed) or, more importantly, the time-of-day, in terms of GMT. It by comparing that GMT with the local time that we deduce the longitude. There's no "LOP which connects all those locations on Earth that have a given, fixed difference DT between the meridian passages of sun and moon." At any moment that DT is the same everywhere. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. "Confidentiality and Privilege Notice The information transmitted by this electronic mail (and any attachments) is being sent by or on behalf of Tactronics; it is intended for the exclusive use of the addressee named above and may constitute information that is privileged or confidential or otherwise legally exempt from disclosure. If you are not the addressee or an employee or agent responsible for delivering this message to same, you are not authorized to retain, read, copy or disseminate this electronic mail (or any attachments) or any part thereof. If you have received this electronic mail (and any attachments) in error, please call us immediately and send written confirmation that same has been deleted from your system. Thank you." --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---