Astro Navigation
Join Date: Apr 2010
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Celestial navigation, even robots do it,
Regarding Snark.
Greatly disapointed to read that the charts had Ascension wrong, next thing we'll be hearing that the RAF got Australia in the wrong spot...
Celestial guidance was first used (automatically) in the American Snark missile (Nortronics stellar-inertial guidance) first flown on 06/08/1953. It uses star positioning to fine-tune the accuracy of the inertial guidance system after launch.
By 1958 the celestial navigation system used by the Snark allowed its most accurate test, which appeared to fall 4 nautical miles (7.4 km) short of the target. However, this apparent failure was at least partially because the British Navigation Charts used to determine the position of Ascension Island were based on position-determination techniques less accurate than those used by the Snark. The missile landed where Ascension Island would be found if more accurate navigation methods had been used when developing the chart
I don't own this space under my name. I should have leased it while I still could
But charting was the province of the Navy. The Navy would say where Ascension was and then the RAF would photograph it and the RE would map it.
Madeira to Bermuda is a little more difficult than Guzz to the East Coast! Not much I'll grant you, but get the DR wrong by more than 30 miles and you're in the poo!
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Sunset
Can any of you brilliant chaps out there tell me how to calculate by how many minutes sunset is delayed for every degree west you go ( in the northern hemisphere)?
Canadian Break,
Have a look here Variation in Time of Sunrise
It covers both sunrise and sunset, but you might want to get a strong coffee before you start reading though
Have a look here Variation in Time of Sunrise
It covers both sunrise and sunset, but you might want to get a strong coffee before you start reading though
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"how many minutes sunset is delayed for every degree west you go "
Err, isn't it simply derived from minutes in a day divided by 360
ie; 11540/360
=4
ie sunset is delayed 4 mins/degree west.
Latitude is irrelevant to the affect of purely westerly travel. OK you might not get a sunset in some places, but the sun will still appear to travel at 1 degree every 4 mins.
Or have a made some stupid gaff and should I delete this post to avoid deep personal shame?
Err, isn't it simply derived from minutes in a day divided by 360
ie; 11540/360
=4
ie sunset is delayed 4 mins/degree west.
Latitude is irrelevant to the affect of purely westerly travel. OK you might not get a sunset in some places, but the sun will still appear to travel at 1 degree every 4 mins.
Or have a made some stupid gaff and should I delete this post to avoid deep personal shame?
I don't own this space under my name. I should have leased it while I still could
Smoke, I'm with you.
The best examples, or should I say experiences, come on crise ships. Leaving Southampton and arriving Dublin 2 days later one enjoys a few extra minutes of daylight.
Sunset is always 4 minutes later for every degree of longitude that one travels west at the same latitude. If you moved west and also changed your latitude then sunset time would change by both longitude transport and also by sun altitude for latitude change.
The best examples, or should I say experiences, come on crise ships. Leaving Southampton and arriving Dublin 2 days later one enjoys a few extra minutes of daylight.
Sunset is always 4 minutes later for every degree of longitude that one travels west at the same latitude. If you moved west and also changed your latitude then sunset time would change by both longitude transport and also by sun altitude for latitude change.
But charting was the province of the Navy. The Navy would say where Ascension was and then the RAF would photograph it and the RE would map it.
It was astro nav - or rather using the astro compass one evening - that allowed Frank E.... to prove that Gan was actually 1 mile South of the Equator rather than 1 mile North (or maybe the other way round). The position had remained 'as was' since the Navy had first plotted it and then used it as their secret 'Port T'.
Certainly remember having to learn to do Manual Air Plot during MOTU as a pilot (we were supposed to know how to do every other role in the ac), and still find I use some of the elements of that instruction whilst discussing nav at DHFS.
At least I'll never again hear those dreaded words 'Steady for Astro' whilst flying at low level in gale force winds!
"Mildly" Eccentric Stardriver
Don't forget that when using a watch, it must be on local time, not daylight saving. Always a fun few minutes when visiting a stately home in summer. Stand near the sundial and listen to people explaining to one another why the time is an hour out.
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Anyone remember Rog Howe?
...and then there was the late Geoff Bashford, who was 5 ft nothing. Not only did he need the Astro stool at its max height but he tip-toed to reach the eye-piece. AND the eye-piece was at the lowest point! Can't imagine Geoff doing a 2-minute shot while maintaining the 'tip-toe' posture. A fine nav instructor and a true gentleman.
Gentleman Aviator
Stand near the sundial and listen to people explaining to one another why the time is an hour out.
You must also consider arc to time for the real local time and also the Equation of Time, as "Mean Time" is only a convenient average. (There's a clue in the name!)
"Mean Time"
