NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Lunar Distances v. Meridian Angles
From: Chuck Griffiths
Date: 2002 Feb 26, 13:07 -0500
From: Chuck Griffiths
Date: 2002 Feb 26, 13:07 -0500
OK, I know George H. promised he'd cover using moon altitudes in place of lunar distances in his next part but I'm going to go ahead and jump the gun by asking a question. Now that George has helped me start to understand lunar distances I can't help but consider an alternative approach to finding GMT. Why can't we observe the altitude of the moon and one other body and, using our assumed latitude, solve for the meridian angle of both bodies. The difference between the two angles should change by the rate at which the moon moves through the sky faster than another body. If that's true, can't we find the meridian angle between the two bodies for the even hours, say on either side of what time we think it is, and use the same inverse linear interpolation approach to find the time of our sight? Of course, I can think of a couple issues with this approach worth discussion. First, this only works when the altitude of the moon and the other body change reasonably with time, i.e., we can't do it when either body is close to being a meridian sight. Second, we need both altitudes simultaneously. I think this could be solved by alternately observing one body then the other several times and graphing the sights so that we could derive an averaged simultaneous altitude from the graph. Lastly, why bother when the other methods thus far described work? It seems to me that if this is a workable solution it provides a method of checking time using techniques that are already in most navigator's "bag of tricks". That is, we get to correct for refraction, horizontal parallax, augmentation, etc. using the tabular methods we use for other sights. Chuck Griffiths ********************************************************************** This e-mail and any files transmitted with it are confidential and may be legally privileged or otherwise exempt from disclosure under applicable law. This e-mail and its files are intended solely for the individual or entity to whom they are addressed and their content is the property of Smiths Aerospace. If you are not the intended recipient, please do not read, copy, use or disclose this communication. If you have received this e-mail in error please notify the e-mail administrator at postmaster@si.com and then delete this e-mail, its files and any copies. This footnote also confirms that this e-mail message has been scanned for the presence of known computer viruses. ***********************************************************************