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seb146
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Ancient Navigation

Sat Oct 10, 2015 4:21 am

How did people find Hawai'i and Fiji in the 1700s? I understand Columbus sailing across the Atlantic knowing he was going to find land, but a tiny island in the world's biggest ocean? How did Captain Cook do it?
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zckls04
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RE: Ancient Navigation

Sat Oct 10, 2015 4:46 am

They used the stars.

I recommend "Longitude" by Dava Sobel. Latitude has always been relatively easy to calculate, but longitude relies on having accurate time. That book tells the story of the advances which allowed navigators to accurately measure longitude, and thus figure out where the stars ought to be.

Of course even with a reasonably accurate longitude and latitude, you need a fair bit of luck to hit something as small as Hawaii. But possibly not as much as you might think. The margin of error is pretty high if you can sail around a bit. You just need to get within 20 miles or so and you'll probably spot Mauna Kea.
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seb146
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RE: Ancient Navigation

Sat Oct 10, 2015 6:09 am

Quoting zckls04 (Reply 1):
They used the stars.

IIRC, there was a long boat of men paddling from Tahiti to Hawai'i a few years ago. Using only the stars and ocean currents, they found it. The first one or two is what I am talking about. After six or so, they knew and could tell each other how far, how many days and so on.

It just staggers my mind how this happened.

We can see Molokai from O'ahu so that is not the issue. How can someone find Fiji from Chile without Google maps?
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Aesma
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RE: Ancient Navigation

Sat Oct 10, 2015 7:28 am

Are you asking how they discovered them ? By chance is the answer. And true for all islands.

At least those men did it sailing vessels that were maneuverable, could carry a lot of food and water, etc.

What is really amazing is how the Polynesians got there.
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Airstud
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RE: Ancient Navigation

Sat Oct 10, 2015 7:43 am

Quoting seb146 (Thread starter):
How did people find Hawai'i and Fiji in the 1700s? I understand Columbus sailing across the Atlantic knowing he was going to find land, but a tiny island in the world's biggest ocean? How did Captain Cook do it?

You might ask 2707200X. See, all he asks is a tall ship and a star to steer her by.
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flyingturtle
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RE: Ancient Navigation

Sat Oct 10, 2015 9:38 am

Quoting Airstud (Reply 4):
You might ask 2707200X. See, all he asks is a tall ship and a star to steer her by.

 
Quoting zckls04 (Reply 1):
Of course even with a reasonably accurate longitude and latitude, you need a fair bit of luck to hit something as small as Hawaii.

Several times seafarers wanted to visit islands that have already been put on a map, and did not find them due to incorrectly calculated longitudes/latitudes, and found other, previously unknown islands instead...

Quoting zckls04 (Reply 1):
but longitude relies on having accurate time

I've read this book, and I highly recommend it to anybody else! I've heard it's required reading in the vocational training as a watchmaker. The ideas brought forward to ensure this accurate time is sometimes amusing. For example the powder of sympathy... see http://en.wikipedia.org/wiki/Powder_of_sympathy

With a long-wave radio and time signals, they could have solved this thing elegantly, but well... Marconi, Tesla and Edison came a bit late for that.


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pu
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RE: Ancient Navigation

Sat Oct 10, 2015 2:20 pm

The Sobel book mentioned above is good.

When I took navigation and survival classes we had to learn to find our way witbout the stars due to the cloud cover around the Baltic and Arctic. It's harder and less precise than using stars but it can be done. Also, whatever ancient people may have lacked in celestial knowledge they may have made up for in undertsanding more about where birds fly, the look and temperature of the ocean (which can show currents) and even things like the smell of the wind.

There's lots of small details in nature that give clues related to navigation.




Pu.
 
us330
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RE: Ancient Navigation

Sat Oct 10, 2015 3:10 pm

Quoting flyingturtle (Reply 5):
Several times seafarers wanted to visit islands that have already been put on a map, and did not find them due to incorrectly calculated longitudes/latitudes, and found other, previously unknown islands instead...

Or hit a reef that wasn't supposed to be there....

Quoting seb146 (Reply 2):
How can someone find Fiji from Chile without Google maps?

Well, they didn't go from Fiji to Chile necessarily. The Polynesians "island hopped" from east to west over the course of centuries.

While we have a better understanding of "how" they did it, we still don't know "why" or how many vessels/people were lost during the course of Pacific island colonization.
 
MD11Engineer
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RE: Ancient Navigation

Sat Oct 10, 2015 3:53 pm

There is still a way to calculate the longitude by measuring the angular distance between two stellar objects, e.g. the moon and a planet (Lunar distance method). This was used before chronometers became affordable.
Another, very simple technique is the noontime atitude of the sun. As the altitude of the sun(the angle between the centre of the sun and the horizon) will not change much around noon time, but in meantime the geographical position of the sun (the point on earth's surface, where the sun will be seen exactly at 90 degrees overhead), will move at .25 degrees longitude (equals 15 NM per minute over the equator). To get the exact time one can use a simple trick: Record the time when the sun passes a certain angle on the way up and record the time again when it passes the same angle on the way down. The value in the middle will be the exact noon time in this location.

Sorry guys, but I'm just teaching myself celestial navigation, so I'm a bot of an anorak about this topic, means I can bore people to death with it   .
Currently I'm looking for an affordable second hand sextant (not a toy or dummy for decoration, but a serious navigational instrument).

I know that there are a few former naval officers here on this site, who will have better information.

Btw., a decent merchant marine navigating officer was expected to calculate a celestial fix with an accuracy of plus minus 2 NM.

Jan

[Edited 2015-10-10 08:54:47]

[Edited 2015-10-10 08:55:18]
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L0VE2FLY
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RE: Ancient Navigation

Sun Oct 11, 2015 8:02 am

Here's a thread I started a couple years ago you might find interesting...

Navigation Without A Compass (by L0VE2FLY Feb 6 2013 in Non Aviation)

Quoting Aesma (Reply 3):
Are you asking how they discovered them ? By chance is the answer. And true for all islands.

  
.
Quoting Aesma (Reply 3):
At least those men did it sailing vessels that were maneuverable, could carry a lot of food and water, etc.

What is really amazing is how the Polynesians got there.

Indeed, Captain Cook was high tech compared to the Polynesians!


Quoting Airstud (Reply 4):
You might ask 2707200X. See, all he asks is a tall ship and a star to steer her by.

Somebody IM him, he needs to take a break of the Word Game & Five Word Story threads!  
 
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Thunderboltdrgn
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RE: Ancient Navigation

Sun Oct 11, 2015 9:39 am

Quoting seb146 (Thread starter):
How did people find Hawai'i and Fiji in the 1700s? I understand Columbus
sailing across the Atlantic knowing he was going to find land, but a tiny island in the world's
biggest ocean? How did Captain Cook do it?

Well 300 years ago is not really "ancient" and the Vikings crossed the Atlantic some 500 years before Colombus.

See these links for info about how they navigated:
http://www.history.com/news/evidence...led-viking-navigational-tool-found
http://www.vikingeskibsmuseet.dk/en/...on-in-the-viking-age/#.VhouCJem1K8
http://www.bbc.co.uk/schools/primaryhistory/vikings/vikings_at_sea/
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flynhi808
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RE: Ancient Navigation

Tue Oct 13, 2015 5:42 am

Quoting seb146 (Reply 2):
IIRC, there was a long boat of men paddling from Tahiti to Hawai'i a few years ago. Using only the stars and ocean currents, they found it. The first one or two is what I am talking about. After six or so, they knew and could tell each other how far, how many days and so on.

Do you mean Hokule'a and Hikianalia? They are much more than men paddling a long boat.

http://www.hokulea.com

http://en.wikipedia.org/wiki/Hokulea
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NAV30
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RE: Ancient Navigation

Fri Oct 16, 2015 9:23 am

Quoting seb146 (Thread starter):
but a tiny island in the world's biggest ocean? How did Captain Cook do it?

Hawaii is only the largest of a chain of islands stretching for hundreds of miles - a good proportion of them being mountainous, and visible from many miles away.

http://www.lonelyplanet.com/maps/north-america/usa/hawaii/

Not 'knocking' Cook's undoubted success - but he had a pretty big 'target' to aim at - and probably some information gained by earlier explorers.........  
 
Max Q
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RE: Ancient Navigation

Mon Oct 19, 2015 8:24 am

Quoting NAV30 (Reply 12):
Not 'knocking' Cook's undoubted success - but he had a pretty big 'target' to aim at - and probably some information gained by earlier explorers.........

Yes, he probably just followed Contrails..



Seriously, do you have any idea how tiny those islands are in the biggest ocean on our planet ?
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NAV30
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RE: Ancient Navigation

Mon Oct 19, 2015 1:01 pm

In those days longitude was very difficult to establish precisely, since it needed accurate clocks, Mac Q. But latitude was pretty well as easy to establish as it is today - just a matter of measuring the angle/height of the sun at noon. Even if the clocks were wrong on a long voyage, they could establish latitude accurately simply by measuring the 'angle of sight' until it was at its highest for the day, which 'told' them how far they were from the Equator. As a 'side-benefit,' haven't seen anything about it in the history books, but my guess is that once they'd established the 'highest point' for the day, they re-set the clocks for noon, if necessary..........

My guess is that Cook knew the approximate latitude he needed to find the Hawaiian Islands (which, as I said earlier, stretch for over one hundred miles) and wisely/capably sailed along it until he sighted the islands?

Or are you suggesting that he found the place by pure chance?

[Edited 2015-10-19 06:34:27]
 
slider
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RE: Ancient Navigation

Mon Oct 19, 2015 3:19 pm

Celestial navigation, in various forms, has been around for centuries in a modern sense, but even primitive astronavigation existed back in ancient Egyptian times.

Ironically, the US Navy got rid of it as a curriculum, but is bringing it back in case GPS and electronic navigation gets blacked out (ie: EMP or other cause).

The refinement and advances in navigation over the years are pretty fascinating.
 
IADCA
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RE: Ancient Navigation

Mon Oct 19, 2015 3:38 pm

Quoting seb146 (Thread starter):
How did people find Hawai'i and Fiji in the 1700s? I understand Columbus sailing across the Atlantic knowing he was going to find land, but a tiny island in the world's biggest ocean? How did Captain Cook do it?

In the specific case of the Hawaiian Islands, it was an accident. Cook was sailing from Tahiti to North America to try to find a western approach to the Northwest Passage. He happened to pretty much run straight into Kauai on the way.

Quoting pu (Reply 6):
There's lots of small details in nature that give clues related to navigation.

Polynesians specifically watched bird species and from the presence of certain ones knew when they were within a certain distance of land (although this is only good out to about 50 miles or so).

Quoting NAV30 (Reply 14):
My guess is that Cook knew the approximate latitude he needed to find the Hawaiian Islands (which, as I said earlier, stretch for over one hundred miles) and wisely/capably sailed along it until he sighted the islands?

By the time of Cook's second and third voyages - which went to Hawaii - they did have chronometers in the Royal Navy (and he had one onboard), although not that many. For example, there was only one on the entire First Fleet to Australia.
 
Max Q
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RE: Ancient Navigation

Tue Oct 20, 2015 8:00 am

Quoting NAV30 (Reply 14):
Or are you suggesting that he found the place by pure chance?

Don't know but in retrospect he probably wished he hadn't.
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RE: Ancient Navigation

Tue Oct 20, 2015 9:35 am

Quoting slider (Reply 15):
Ironically, the US Navy got rid of it as a curriculum, but is bringing it back in case GPS and electronic navigation gets blacked out (ie: EMP or other cause).

They surely still have INS as a backup, and I thought that they still used sextants, but scrapped the almanach in favor of a independent, portable computer which computes Lon/Lat given the sextant measurement, the star observed, and the date and time...


David
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NAV30
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RE: Ancient Navigation

Tue Oct 20, 2015 11:34 am

Quoting IADCA (Reply 16):
For example, there was only one on the entire First Fleet to Australia.

Interesting point, IADCA. History records that the Admiralty was notoriously 'penny-pinching,' but that 'takes the cake.'

One has very much to admire the guys who 'made it' with such limited resources.

[Edited 2015-10-20 05:04:01]
 
us330
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RE: Ancient Navigation

Tue Oct 20, 2015 12:20 pm

Quoting Max Q (Reply 13):

Seriously, do you have any idea how tiny those islands are in the biggest ocean on our planet ?
Quoting NAV30 (Reply 14):
My guess is that Cook knew the approximate latitude he needed to find the Hawaiian Islands (which, as I said earlier, stretch for over one hundred miles) and wisely/capably sailed along it until he sighted the islands?

Or are you suggesting that he found the place by pure chance?

Pure chance, considering that he was the first recorded European to encounter the islands. There is some dispute as to whether or not a Spanish galleon had first encountered the Hawaiian islands, but it is unlikely that even if they had, and Cook had the records/knew about such activity, that the information would be detailed enough for him to chart a direct course for them. The Spanish also had a policy of confidentiality for encountering islands previously unknown to the west, so even if they did encounter them, it is unlikely that such information would be disclosed to the British.

See: https://en.wikipedia.org/wiki/Ruy_L%C3%B3pez_de_Villalobos
 
MD11Engineer
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RE: Ancient Navigation

Thu Oct 22, 2015 5:51 pm

Quoting flyingturtle (Reply 18):

They surely still have INS as a backup, and I thought that they still used sextants, but scrapped the almanach in favor of a independent, portable computer which computes Lon/Lat given the sextant measurement, the star observed, and the date and time...

You can still get the printed almanac and the sight reduction tables (H.O. 229 resp. H.O. 249) and they are pretty cheap. Sextants are another matter. Most sextants sold e.g. on eBay are junk made in India only fit for decorative purposes (e.g. on a book shelf). A serious sextant, e.g. made by Cassen & Plath in Hamburg, will set you back at least $ 500.
There exist cheaper sextants made from plastic by the American company Davis, but their cheapest product, the Mk3 sextant (originally developed for the US Navy for the use in life boats) is in reality only good for training. The better products, the Mk.15 or the Mk 25, have mixed reviews. Some whohave used them, praise them, but others consider them to be unreliable. They certainly are more sensitive to temperature changes and need to be adjusted more often, but for a yacht sailor on a small boat tossed around by waves a tolerance of 5 NM is good enough on an ocean crossing. When he gets closer to land, he'll navigate more accurately using landmarks anyway.
Another option would be an East German sextant made by the now extinct company Freiberger Präzissionsmechanik or one of the Soviet copies of these sextants. There also exist good sextants from Japan, or, a bit cheaper, China, but they are also worth at least $ 500.
I have a WW 2 RAF Mk IXa aircraft bubble sextant, which I'm currently restoring, but due to it's design it cannot be used on ships and is less accurate than a naval metal sextant.

As for nautical chronometers, time signals broadcast via HF and cheap quartz watches have made them obsolete. The mechanical ones were expensive technical miracles, which had to be calibrated once a year and were not to be removed from their transport case. Every winding of the clock spring had to recorded in a chronometer log, as was the daily error (compared to the time signal received by radio).

Jan
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Flighty
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RE: Ancient Navigation

Thu Oct 22, 2015 7:44 pm

Quoting flyingturtle (Reply 18):
hey surely still have INS as a backup, and I thought that they still used sextants, but scrapped the almanach in favor of a independent, portable computer which computes Lon/Lat given the sextant measurement, the star observed, and the date and time...

How accurate is a computerized sextant? Seems like it would be pretty good?
 
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RE: Ancient Navigation

Thu Oct 22, 2015 8:11 pm

Quoting Flighty (Reply 22):
How accurate is a computerized sextant? Seems like it would be pretty good?

Computerized sextant? No, I've never heard of such a thing...

I wrote about the almanach book and the mathematics being replaced by a computer, while still using the old sextant. By entering the values from the sextant, the computer gives you longitude and latitude.


David
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Kiwirob
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RE: Ancient Navigation

Thu Oct 22, 2015 8:50 pm

Quoting seb146 (Thread starter):
how did Captain Cook do it?

He already had a pretty good idea that they were there. Abel Tasman had already sighted Fiji and Tonga.

Quoting us330 (Reply 7):
Well, they didn't go from Fiji to Chile necessarily. The Polynesians "island hopped" from east to west over the course of centuries.

It's fairly well proven that Pacific Islanders did get to South America, they brought back the potato to the islands from there.

Quoting thunderboltdrgn (Reply 10):

Well 300 years ago is not really "ancient" and the Vikings crossed the Atlantic some 500 years before Colombus.

There's also a number of people who believe that the Vikings even made it to New Zealand.

http://www.freerepublic.com/focus/chat/1613129/posts

But we aren't allowed to talk about this in NZ, in case it is actually true (not likely) it would make the indigenous people upset.
 
skywaymanaz
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RE: Ancient Navigation

Sat Oct 24, 2015 8:00 am

Before longitude could be accurately determined most seafarers would sail north or south to the latitude of their destination first. Maintaining that latitude as they sailed east or west they'd eventually reach their destination. A few other tricks ancient mariners used was knowing which stars were directly overhead at their destination. Arcturus is directly overhead in Hawaii. Sail north from Fiji until Arcturus is overhead then east. By the time of the great age of exploration Polaris was close enough to the north celestial pole to make calculating latitude simple at night. In Roman times Kochab was the nearest star to the pole but it was more than 5° off so not as useful. Beta Hydri may have been a useful southern pole star at that time for any south pacific navigators though.
 
MD11Engineer
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RE: Ancient Navigation

Sat Oct 24, 2015 5:16 pm

Quoting skywaymanaz (Reply 25):
Before longitude could be accurately determined most seafarers would sail north or south to the latitude of their destination first. Maintaining that latitude as they sailed east or west they'd eventually reach their destination. A few other tricks ancient mariners used was knowing which stars were directly overhead at their destination. Arcturus is directly overhead in Hawaii. Sail north from Fiji until Arcturus is overhead then east. By the time of the great age of exploration Polaris was close enough to the north celestial pole to make calculating latitude simple at night. In Roman times Kochab was the nearest star to the pole but it was more than 5° off so not as useful. Beta Hydri may have been a useful southern pole star at that time for any south pacific navigators though.

The Norsemen sailed to Iceland, Greenland and Northern america in relatively short legs, not more that a week of sailing, but with their northerly route out of Scandinavia they had to go westwards against the Gulf Stream and the prewailing winds.
Columbus (and possibly others) discovered the Trade Wind zone north of the equator, where there are steady winds blowing westwards. Conveniently for Columbus the Spanish Canary Islands are located in this zone. The big sailing ships up to the early 20th century and today's blue water yachties use this route as wellto cross the Atlantic. They sail southwards along the Portugese and West African coast and then head out westwards to the Canaries. There they re-supply and then sail in the trade winds westwards until they reach the coast of Brazil. From there they go north or southwards along the coast again until the reach their destination. The only problrm is that if you stray too far south you might get into the Doldrums along the equator, where there is often an enduring calm (no winds). They also have to cross the hurricane belt, so they have to watch out for the season. For a return to Europe they go north and follow the Gulf Stream, using the westerly winds in this region.

Jan
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rwessel
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RE: Ancient Navigation

Sat Oct 24, 2015 5:35 pm

Quoting flyingturtle (Reply 23):
Quoting Flighty (Reply 22):
How accurate is a computerized sextant? Seems like it would be pretty good?

Computerized sextant? No, I've never heard of such a thing...

The Astro-Inertial system used on the SR-71 is at least (in the "astro" part) plausibly a "computerized sextant".
 
MadameConcorde
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RE: Ancient Navigation

Sat Oct 24, 2015 5:54 pm

History of Hawaii

Sometime around 1 AD, the earliest Polynesian settlers began to populate the islands. Around 1200 AD Tahitian explorers found and began settling the area as well. This became the rise of the Hawaiian civilization and would be separated from the rest of the world for another 500 years until the arrival of the British.

read more:
https://en.wikipedia.org/wiki/History_of_Hawaii

The Bishop Museum in Honolulu has a whole section on how the Hawaiian Islands were first populated and the first voyages of Polynesians from the Marquesas Islands to the Hawaiian Islands.
I strongly recommend a visit to the Bishop Museum to all those who are planning to go to the Hawaiian Islands.

http://www.bishopmuseum.org/research/cultstud/anthro.html

http://www.bishopmuseum.org/exhibits/

     
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RE: Ancient Navigation

Sat Oct 24, 2015 6:43 pm

Quoting rwessel (Reply 27):
The Astro-Inertial system used on the SR-71 is at least (in the "astro" part) plausibly a "computerized sextant".

Thanks, I forgot this one and those on spacecraft!


David
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Flighty
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RE: Ancient Navigation

Sat Oct 24, 2015 7:23 pm

Quoting kiwirob (Reply 24):

There's also a number of people who believe that the Vikings even made it to New Zealand.

Just want to point out that plenty of Chinese and everybody else made it to the Americas. Boats float. Making it there ALIVE is another thing entirely  
Quoting flying-turtle reply=23:

I remember hearing the Apollo moon mission and other space probes used celestial navigation by computer. It seems ideally suited to electronic sensors and so on.
 
nomadd22
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RE: Ancient Navigation

Fri Nov 06, 2015 4:27 pm

Quoting zckls04 (Reply 1):
You just need to get within 20 miles or so and you'll probably spot Mauna Kea.

More like 150 miles from a crow's nest.
Anon
 
PhilBy
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RE: Ancient Navigation

Fri Nov 06, 2015 5:04 pm

Quoting flyingturtle (Reply 23):
Computerized sextant? No, I've never heard of such a thing...

When setting up a modern computerised telescope you point it at three known stars to pinpoint your location.
 
MD11Engineer
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RE: Ancient Navigation

Sat Nov 07, 2015 8:13 am

Quoting PhilBy (Reply 32):
Quoting flyingturtle (Reply 23):
Computerized sextant? No, I've never heard of such a thing...

When setting up a modern computerised telescope you point it at three known stars to pinpoint your location.

The problem with a ship is that it is not a stable platform. It rolls, yaws and pitches with the waves. A sailor with a handheld sextant (with a little practice) can equalise these movements and get a decent measurement. a computer controlled sextant would need a gyro platform and actuators to keep it stable and aligned on the horizon, and would probably be exorbitantly expensive.

Jan
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autothrust
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RE: Ancient Navigation

Tue Nov 10, 2015 12:24 pm

Quoting MD11Engineer (Reply 8):
Sorry guys, but I'm just teaching myself celestial navigation, so I'm a bot of an anorak about this topic, means I can bore people to death with it

No you don't bore anyone, please go ahead. I'm very interested in celestial navigation.

Btw, the Apollo Guidance and Navigation System Sextant did in principle work like a normal sextant, right?

Quoting flyingturtle (Reply 23):
Computerized sextant? No, I've never heard of such a thing...

The Apollo Sextant was quite computerized.
Flown on: DC-9, MD-80, Fokker 100, Bae 146 Avro, Boeing 737-300, 737-400, 747-200, 747-300,747-400, 787-9, Airbus A310, A319, A320, A321, A330-200,A330-300, A340-313, A380, Bombardier CSeries 100/300, CRJ700ER/CRJ900, Embraer 190.
 
MD11Engineer
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RE: Ancient Navigation

Tue Nov 10, 2015 12:43 pm

Quoting autothrust (Reply 34):
Btw, the Apollo Guidance and Navigation System Sextant did in principle work like a normal sextant, right?

In the end a sextant is just a precission device to measure the angle between two objects at the position of the observer. I think that finding stars from a position on a spacecraft is easier, as there is no haze, no clouds and no dodgy horizon line.
In nautical navigation sightings are rarely taken at night, as then it is almost impossible to make out the horizon. Aircraft navigation introduced bubble sextants, which simulate a horizontal plane using a bubble like in a builder's spirit level, but they are less accurate (I have a RAF Mk.IX a sextant from WW2 at home. It even has a built-in stop watch for time keeping, as the aircraft navigator did not have an assistant to take the exact time when the sighting was take, to an accuracy of a second. The stopwatch would be started the moment the navigator got a clear sight and then the time elapsed deducted of the accurate time of te chronometer to get the excact sighting time. Yacht sailors, who also have to do this alone, usually use a sports stop watch in their right hand).
Sightings of planets and stars usually get taken at dawn and dusk and the sun during the day (mostly at noon).

In coastal navigation sextants e.g. can be used in a horizontal position to measure the angle between two landmarks, which would directly result in a fix.

Jan
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autothrust
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RE: Ancient Navigation

Tue Nov 10, 2015 1:05 pm

Thanks for your explanations, as i know the Apollo Sextant needed also a Landmark.

This video did help me a lot to understand the process:

https://youtu.be/YIBhPsyYCiM

With seasextant you have also to cope the waves. So essentialy you are without a clue at night how good you navigation is (of course there is polar light) as you cannot see the horizon?
Flown on: DC-9, MD-80, Fokker 100, Bae 146 Avro, Boeing 737-300, 737-400, 747-200, 747-300,747-400, 787-9, Airbus A310, A319, A320, A321, A330-200,A330-300, A340-313, A380, Bombardier CSeries 100/300, CRJ700ER/CRJ900, Embraer 190.
 
MD11Engineer
Posts: 13916
Joined: Sun Oct 26, 2003 5:25 am

RE: Ancient Navigation

Tue Nov 10, 2015 2:38 pm

Quoting autothrust (Reply 36):
With seasextant you have also to cope the waves. So essentialy you are without a clue at night how good you navigation is (of course there is polar light) as you cannot see the horizon?

More or less. But you are not taking sightings all the time. In bad weather, with overcast sky, you sometimes cannot see any celestial objects for days. During this time you navigate by "dead reckoning": You estimate your current position based on your last known one and your progress (speed, distance and compass course). As soon as you can get a fix (meaning an accurate determination of your position using landmarks, radio bearings, radar or the stars), you'll make a correction, e.g. for drift due to ocean currents and wind.
This is ok out on the open sea, but close to the coast you need to use landmarks, bouys or radar for navigation, as they are more accurate. On the open sea it doesn't matter ifyou are a few miles off your estimated position, but close to the coast there are reefs and sand bars, and you need to know where you are within a few metres (less than 100 metres).
This is why celestial navigation is used out of sight of land.

Jan
Je Suis Charlie et je suis Ahmet aussi
 
rfields5421
Posts: 5907
Joined: Thu Jul 19, 2007 12:45 am

RE: Ancient Navigation

Thu Nov 12, 2015 12:49 pm

Quoting seb146 (Thread starter):
How did people find Hawai'i and Fiji in the 1700s? I understand Columbus sailing across the Atlantic knowing he was going to find land, but a tiny island in the world's biggest ocean? How did Captain Cook do it?

Blind assed luck...

Magellan departed the tip of South America and set out across the Pacific - and only sighted two small reefs - before finding an island - Guam. Over 9,000 miles, near 15,000 km for over four months.

Quoting seb146 (Reply 2):
Using only the stars and ocean currents, they found it.

But they knew the islands existed and where they were located before they started out. That gave them a place to navigate toward.

Discover of islands by the Europeans, and Asians, was done by sailing until they saw something. Sometimes they could pass within a very few miles of a major island and never see anything. Other times they could sail blindly into a reef/ shore of a major island without seeing it and be shipwrecked, or just disappear.

By the 1700s, the explorers like Captain Cook had enough information to expect that some of the major islands existed and approximately where they might be located, but it was literally hit or miss as they tried to find and chart those islands.
 
skywaymanaz
Posts: 719
Joined: Sun May 06, 2012 1:00 pm

RE: Ancient Navigation

Sat Nov 14, 2015 10:35 pm

If anyone is interested in learning "modern" celestial navigation Chris Nolan did a nice series of teaching videos. I got interested in it myself more from the air navigation perspective and his series is nautical. The main difference between the two is air navigation is designed to do the calculations faster but less accurately. There seems to be a revival in learning this lost art in recent years. Pen and paper don't need batteries after all. The terms seem intimidating but the math is fairly easy once you get past the 360/60 DMS format instead of the normal base 10.

http://www.youtube.com/playlist?list...PLah9ocjQNN0Zr7-oKE58wTzXE4XaQU64E

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