A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David C
Date: 2020 Oct 10, 01:45 -0700
The celestial line of position is the key navigation construct that we get from each celestial sight. We can get it by the intercept method or by time sight calculations. It doesn't matter which we use. Historically, the intercept method offered slight reductions in math work, and that was important when computation was expensive and time-consuming. Those days are gone.
I was searching for a post in which Frank said that long by chron was British slang and that he prefered the term sundial sight. I could not find the post so will jump in here.
Now that computations are "free" the Sumner chord method has (IMHO) advantages over both the Sumner tangent method and the intercept method. In the chord method you choose two latitudes and calculate corresponding longitudes. This gives two positions - plot them on the worksheet and draw a line between them. Easy! In the tangent method you calculate one longitude and an azimuth. You then have the hassle of plotting an angle. The intercept method also involves plotting an angle.
I was browsing an 1881 pdf of Raper (first edition 1840) and found the following:
"The longitude by chronometer may be ascertained whenever the time is obtained. The long. by chron. is thus the most efficient check on the long. by account...."
In addition a pdf of Norie for 1836 uses the term Longitude by Chonometers. Long. by Chron. is thus a historically correct abreviation for the time sight method. In the interests of historical accuracy I have decided to revert to using the term long. by chron. (note the full stops)!!!!!