Celestial navigation practices

H

Harland Duzen

Member
Thanks, but Wikipedia says:
'On 12 November, at 9:56 am, an SOS was sent out giving her position as latitude 37° 35' N. and longitude 71° 81' W., which was incorrect by about 37 miles. The SOS was repeated at 11:04 am.'


That not the best way to state your case... :confused:

To be fair, this statement is given a footnote / source as having came from the this paper:

"United States District Court for the Southern District of New York (24 May 1932). "Vestris – Decision on the Merits". Retrieved May 14, 2015."

Whether the paper itself is accurate is another matter, but at least it wasn't conjured from air.
 
B

Bastian Busse

Member
Was navigated on the Titanic with sextants or already via radio navigation?
 
Doug Criner

Doug Criner

Member
For a fix, a sextant was used to measure the angle of a star or other celestial body above the horizon. That angle and the exact time, along with a nautical almanac, would allow plotting a line of position. The intersection of several such LOPs would be the fix.
 
Doug Criner

Doug Criner

Member
Radio navigation, such as LORAN, was decades away in the future.
 
  • Like
Reactions: Mike Spooner
Samuel Halpern

Samuel Halpern

Member
The development of radio had not progressed to the point where it could be used for navigation. Transmission was not continuous. It was by pulsed energy created by arcing high voltage electrical impulses across a spark gap. Communications was by Morse signaling.
 
  • Like
Reactions: Mike Spooner and (deleted member)
Dave Gittins

Dave Gittins

Member
By 1912 the USN had been experimenting with sending radio times signals, so chronometers could be checked. Progress was very limited and nobody used it regularly.

One good feature of 1912 navigation was that the calculations used gave latitude and longitude directly, with no plotting on a chart required. Only Extra Masters had to know how to plot position lines and many mistrusted the newer methods.
 
  • Like
Reactions: 1 person
Mike Spooner

Mike Spooner

Member
I thought Captain Rostron mistake was the fact that Boxhall gave him the wrong position to head for!
 
A

A. Gabriel

Member
You know now that I think of it, we haven't really had a dedicated thread for navigational art and practice in 1912, so I figured this would be a good place to start. But now is also the time for me to reveal the depths of my ignorance regarding such an arcane and interesting topic -- this is a subject on which I have only dared look into very recently so pardon if I come across as an absolute buffoon talking out of the wrong end of the GI tract.

So far from what I've read of the inquiry transcripts I can only find passing references to taking star sights for latitude and longitude from 4th Officer Boxhall's testimony. Many articles written by members more experienced than myself also mention the noon sight for latitude -- Dave Gittins in particular has an article somewhere here detailing the various navigational techniques expected of different levels of certification.

One question I have regarding the noon sight is whether the chronometer was used for the calculation of latitude? I know the method of latitude by noon sight involves the use of solar declination tabulated in the Nautical Almanac but I'm not sure if the chronometer was a must for this technique in those days.
 
Samuel Halpern

Samuel Halpern

Member
The noon latitude sight had been around long before the chronometer was invented.
 
Doug Criner

Doug Criner

Member
The chronometer simplified calculation of longitude. If you know the GMT of local apparent noon (when the maximum altitude of the sun is measured with a sextant), then that will give you the longitude, even without a nautical almanac. Latitude in the northern hemisphere was measured by the altitude of Polaris, long before the advent of chronometers. Before the chronometer, mariners used an hour glass to "sort of" keep track of time, but that was very rough. Magellan's crew, upon sailing around the world, lost track of a whole day, and were totally mystified. (I say Magellan's "crew," because Magellan himself was killed by natives before returning.)

Columbus "discovered" North America before the advent of the chronometer - so he was perhaps uncertain of his longitude. That allowed him to believe (or claim) that he had reached China.
 
Last edited:
A

A. Gabriel

Member
Magellan's crew, upon sailing around the world, lost track of a whole day, and were totally mystified. (I say Magellan's "crew," because Magellan himself was killed by natives before returning.)

Ironically Magellan’s voyage (whose quincentenary is already under way this year) is part of the reason I’m asking this question haha. Latitude by solar noon makes use of tables of solar declination throughout the year, but from what I could find the declinations are tabulated only for Greenwich apparent noon and mean noon (I’ve also seen American nautical almanacs with declinations tabulated for Washington apparent noon and mean noon).

I guess what I’m trying to get at here is did they use a given declination value for the day as-is in calculating for latitude, or did they have to extrapolate the tabled value to correct for the time difference between Greenwich and their location?

[Bonus side note, I’ve actually visited the place where Magellan was killed. It helps that I’m actually from the Philippines itself haha, the fact that we killed him is kind of a big deal in our history.]
 
Dave Gittins

Dave Gittins

Member
Actually, the better you know UTC, the more accurately you can get latitude. Tables give the declination of the sun as it changes throughout the year. In April declination is increasing at about 22' every 24 hours. When you look up the tables, you can interpolate the exact declination for the time of your sunsight if you know UTC. Every 1' error in the declination is a mile error in latitude. On Titanic the UTC could be checked from the chronometer but earlier navigators used a bit of rough judgement. In any case, their instruments were not much use. Magellan would have used an astrolabe, which gave quite crude results. I've seen observations by Francis Drake that are a good degree out.

By the way, you can't get an accurate longitude from the noon sight. The sun seems to hang in the sky for some time and you can't get the exact time of its maximum altitude. Lazy yachtsmen have been know to try this, but it would never do on a properly run liner.

All sorts of rough methods have been used. The yachtsman Vito Dumas, in the Southern Ocean, got longitude by comparing his time of sunset at his guesstimated position with the time of sunset at Greenwich. He was only trying to find South America, so he managed quite well.

Hooray for GPS!
 
Top