NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Latitude by Spica
From: Kieran Kelly
Date: 2004 Jan 12, 15:14 +1100
From: Kieran Kelly
Date: 2004 Jan 12, 15:14 +1100
Frank reed wrote: >Celestial Navigation almost never involved stars in the 19th century (except for lunars). I >found ONE example of a star sight. It's from the whaleship Stonington in the spring of 1847 >out in the middle of the Pacific. It's such a rare thing that I thought it would be worth >separate mention here. He then mentions the Stonington officers performing a lat observation of the star Spica saying "it appears the officers were looking for some entertainment." Hate to disagree but the use of Meridian Passage of stars to determine latitude was very common in land based exploration. The Australian explorer Augustus Gregory used meridian passage of stars virtually every night during the two years of the North Australian Expedition 1855-56. He is on record as saying that he preferred a star's meridian passage over the sun as; 1) It was more accurate 2) It removed the need for a lengthy noon time halt 3) It reduced the need to unpack equipment during the day then re-pack it. 4) It reduced the possibility of native attack during the noon halt. His technique was to shoot the meridian passage of at least two stars culminating in close succession, work out the latitudes and divide by two to get an average latitude. Sometimes he used three stars. I have found his latitude work extraordinarily exact - usually under 400 metres. I would estimate that in the course of his four major exploring expeditions (as compared to his everyday surveying work) he calculated latitude by culmination of stars on about 800 separate occasions. I think the technique was also more commonly accepted in those days than you think. My copies of Raper (1849) and Norie (1852) both contain clear exposition of "Lat by Mer Passage of a star" and appear to give it equal weight to latitude by meridian passage of the sun. I don't think we should fall into the trap of believing that sailors were the only ones to hoist a sextant in the Nineteenth century. I am sure there were just as may surveyors and explorers peering into their mercury horizons in the middle of the night and struggling to read the vernier. Kieran Kelly Sydney Australia