NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
(no subject)
From: Fred Hebard
Date: 2003 May 18, 16:45 -0400
From: Fred Hebard
Date: 2003 May 18, 16:45 -0400
Doug Royer was so kind as to post the data for his shipboard lunars of last week. I looked at them, clearing each one and computing the mean and standard deviation of the difference in the cleared observed distance and the computed distance, as well as the difference between the known time and the time determined from the lunar. Young's method for objects of known altitude was used, as outlined by George Huxtable; thus I ignored Doug's observations of the altitude of the bodies, computing them from his known position. For comparison, I show the same summaries for lunars I have taken on dry land, and two that Arthur Pearson's took in the Caribbean aboard a small yacht. For those who have difficulty reading this in a web browser, paste the table into a text processor and it should line up properly. Doug's observation are about as precise as Arthur's and mine as determined by the standard deviation of arc difference. However, the absolute arc difference, and the corresponding time difference, is quite large, almost 5 minutes of arc. Interestingly, Doug's arc difference goes in opposite directions for the Moon, Jupiter observation as compared to the Moon, Spica observation. This leads to very similar time differences for the two observations. In the Moon, Jupiter observation, Doug brought Jupiter to the near side of the Moon, but Spica needed to be brought across the face. One possibility for the similarity of this discrepancy is that Doug was not bringing the objects all the way to the moon, but, rather, leaving a gap. To determine index error, I use the technique outlined by Bruce Stark, among others, of measuring the semi-diameter of the sun. This technique might sharpen one's skills for lunars, which are measured in a similar fashion. I also have taken the liberty of including two graphs of Doug's data. I haven't heard any complaints yet about including small binaries like this. I hope they come through. Please let me know if they cause a problem, and of course, with any comments on the analysis. Fred mean mean std dev mean Objects n date given UT del arc' del arc' del time" Moon, Jupiter 8 12/27/02 6:36:41 0.884695 0.703781 90.26738 Moon, Aldebaran 7 1/8/03 23:42:01 0.514089 0.830704 -62.1228 Moon, Sun 7 1/11/03 20:33:31 1.219828 1.215593 162.5041 Moon,Sun A. Pearson 7 1/7/03 19:42:07 1.317516 0.404807 169.1811 Moon,Sun A. Pearson 6 1/10/03 18:37:44 1.457861 0.447954 194.242 Moon, Jupiter 5 2/12/03 0:37:40 -0.67918 0.271337 77.6666 Moon, Sun 6 3/9/03 20:40:13 0.981567 1.136952 129.6058 Moon, Jupiter 5 3/10/03 3:53:50 0.693372 0.617291 -83.1301 Moon, Sun 5 3/12/03 22:14:17 1.831421 1.846688 225.4475 Moon, Jupiter 7 4/4/03 1:04:45 4.30333 2.602312 -524.762 Moon, Sun 5 4/5/03 23:04:23 0.760016 0.32473 100.9633 Moon, Jupiter 7 4/6/03 0:20:33 0.209499 0.334972 -25.5961 Moon, Sun 8 4/6/03 18:29:38 -0.03824 0.569998 -5.04673 Moon, Jup D. Royer 6 5/12/03 3:21:47 -5.04648 1.162142 -513.434 Moon, Spica D. Royer 6 5/12/03 5:37:32 4.801561 0.662518 -490.445 Moon, Jupiter, Doug Royer Moon, Spica, Doug Royer