Timers for astro

[TFJ]

Sextant clock

I have never understood why manufacturers of sextants have thought of fixing a digital clock to the sextant so you can take the sight and press a time button to record the actual time of the sight
I have also been trying to find a digital watch that you can stop the time (not a stop watch) but cant find one maybe I have been looking in the wrong place?
Terry

 

[TonyS]

I don't know why you are all so bothered about accuracy. Slocum circumnavigated with a tin clock in 1898. Before Cape Town on the way back he lost the minute hand! He still hit Capetown, St Helena etc on his way back across the Atlantic to the East coast of the USA with no problem at all.

 

[Martin_J]

Hope it's not off topic.... but about the only book I have read cover to cover in one day was 'Longitude' by Dava Sobel... It's all about the creation of the Harrison chronometer in the 18th centruy... in the quest to be able to calculate longitude accurately...

Regarding a watch.. an analogue Citizen eco-drive for me (charged by light so no batteries needed)... and so long as you know how many seconds it gains/loses each month it's easy to work out the real time... Set from an NTP source at work which takes time from satellite and ntp servers simultaneously.

 

[snowleopard]

I don't know why you are all so bothered about accuracy. Slocum circumnavigated with a tin clock in 1898. Before Cape Town on the way back he lost the minute hand! He still hit Capetown, St Helena etc on his way back across the Atlantic to the East coast of the USA with no problem at all.

And do you know how he did it?

 

[Mudisox]

Timing and Astro nav

Best advice I had when they first came out was to buy and use a digital voice recorder, then you can call the time before you begin,separately, let the "tape" run and call each of the sights, with each equal increase/decrease in angle; Don't forget to record the last/first sextant angle and then you can work it all out with a stop watch later, listening to the replay, at your liesure.

 

[timbartlett]

I don't know why you are all so bothered about accuracy. Slocum circumnavigated with a tin clock in 1898.

Of course, in the great scheme of things, you're right. But FWIW, I reckon there are three answers to your (rhetorical?) question:-
1. If one accepts that we now study/practice astro mainly out of interest, rather than necessity, it is far more satisfying to get an accurate result than an inaccurate one -- even evthe inaccurate one would be "near enough" for practical navigation.
2. Crossing an ocean from east to west or vice versa doesn't require great accuracy in Longitude, so long as Latitude is reasonably OK
3. Expectations of accuracy have changed enormously. Only thirty years ago, we used to be quite happy if we set off from the south coast and were within a few miles of our EPs when we found France. No-one, in Slocum's time could have dreamed of the possibility of knowing one's position in mid-ocean to within an armspan, and at any time of night or day.

 

[snowleopard]

Of course, in the great scheme of things, you're right. But FWIW, I reckon there are three answers to your (rhetorical?) question:-
1. If one accepts that we now study/practice astro mainly out of interest, rather than necessity, it is far more satisfying to get an accurate result than an inaccurate one -- even evthe inaccurate one would be "near enough" for practical navigation.
2. Crossing an ocean from east to west or vice versa doesn't require great accuracy in Longitude, so long as Latitude is reasonably OK
3. Expectations of accuracy have changed enormously. Only thirty years ago, we used to be quite happy if we set off from the south coast and were within a few miles of our EPs when we found France. No-one, in Slocum's time could have dreamed of the possibility of knowing one's position in mid-ocean to within an armspan, and at any time of night or day.

Slocum didn't use the methods we use today. I believe he used Lunar Distances. Wikipedia says:

"In celestial navigation, lunar distance is the angle between the Moon and another celestial body. A navigator can use a lunar distance (also called a lunar) and a nautical almanac to calculate Greenwich time. The navigator can then determine longitude without a marine chronometer."

So he didn't settle for the inaccuracy of the tin clock with just an hour hand.

 

[smartcom]

GPS receivers do output UTC, and of course this includes correcting for leap seconds. Any delay may be in the time lag in updating the display, or of outputting the data in NMEA0183 (typically sent once a second), and then that sentence being decoded and displayed.
If you want high accuracy, a sailor friend of mine runs Quartzlock (www.quartzlock.com), who do high resolution timers - they reckon their best one is accurate to 1 second in the life of the universe!