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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars for dummies like me
From: Frank Reed CT
Date: 2004 Sep 25, 22:38 EDT
From: Frank Reed CT
Date: 2004 Sep 25, 22:38 EDT
Jan K wrote:
"During the twilight, you can e.g. take three altitudes of the Moon and Regulus and three distances between those two bodies without even marking the time. Average both sets of altitudes and the set of the distances. You then have the distance and altitudes for the same moment. Now from the cleared distance you have GAT and from the altitude of the Regulus (if not being too near to the meridian) you will find LST (using the DR latitude); change it to LAT and gain the longitude from LAT - GAT. You don't need any clock, you can limit yourself to the sandglass for ringing the bell and cooking eggs."
Yes, you're right, and twilight is not even a limitation. Although lunars by stars were much rarer, I should not have implied that they were not done. Even in the middle of the night, the horizon can be seen well enough for the altitude sights in a set of lunars. A 5 minute error in altitude, which in late 20th century celestial would have been considered very bad, would yield perhaps a 7 minute error in longitude (from the time sight) in typical latitudes and that was sometimes acceptable given the known limitations of lunars. Supposedly Nathaniel Bowditch himself greatly prefered lunars using stars because the Sun hurt his eyes.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
"During the twilight, you can e.g. take three altitudes of the Moon and Regulus and three distances between those two bodies without even marking the time. Average both sets of altitudes and the set of the distances. You then have the distance and altitudes for the same moment. Now from the cleared distance you have GAT and from the altitude of the Regulus (if not being too near to the meridian) you will find LST (using the DR latitude); change it to LAT and gain the longitude from LAT - GAT. You don't need any clock, you can limit yourself to the sandglass for ringing the bell and cooking eggs."
Yes, you're right, and twilight is not even a limitation. Although lunars by stars were much rarer, I should not have implied that they were not done. Even in the middle of the night, the horizon can be seen well enough for the altitude sights in a set of lunars. A 5 minute error in altitude, which in late 20th century celestial would have been considered very bad, would yield perhaps a 7 minute error in longitude (from the time sight) in typical latitudes and that was sometimes acceptable given the known limitations of lunars. Supposedly Nathaniel Bowditch himself greatly prefered lunars using stars because the Sun hurt his eyes.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
