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Old 01-08-2020, 17:45   #31
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Re: wood ships , iron men

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Originally Posted by StuM View Post
Doh! That's what you get when thinking from a southern hemisphere perspective.



Ha! That reminds me of the time I bought a celestial navigation program (AstroNav by NavSoft, great program, BTW) and noticed that the diagram showing the illuminated fraction of the Moon was backwards. I emailed the developer to inform him of his "error", and he politely pointed out that in the Southern Hemisphere that's how it looks.
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Old 01-08-2020, 18:50   #32
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Re: wood ships , iron men

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Picky, picky, picky. My bad and what you posted is true; but completely missed the point of my post.

With out an ephemeris nothing else matters.
Not really, if you had a good clock and observed the local time when a star was at maximum altitude you could derive your longitude from the time difference.

Latitude can be worked out from first principals if you know the solistices.
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Old 02-08-2020, 04:35   #33
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Re: wood ships , iron men

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... But returning to a specific location such as one's home port was - I dare say - not an uncommon skill amongst pre-chronometer mariners. Otherwise I don't think sailing would have really taken off.
We used to go fishing beyond sight of land. After moving around from spot to spot, and drifting a lot, we didn't really know our starting location. We usually had a compass, but it wasn't much more help than just glancing at the position of the sun.

With that, we got close enough to see a landmark. Our best one was three hills which ran roughly North-South. If the big one was on the left, and they were evenly spaced, we were due East. If they were starting to line up, we were farther North. With that, we could adjust course a little. As we got closer, more landmarks would appear. By the time we got to our home harbor, we'd been steaming a straight line in for some time.

Granted, we weren't crossing oceans. And explorers back in the day did sometimes get blown off their DR course by storms and ended up seeing unfamiliar landmarks when approaching shore. This is why early charts always had profiles of the land, as they would first appear to an approaching sailor.
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Old 02-08-2020, 11:50   #34
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Re: wood ships , iron men

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Not really, if you had a good clock and observed the local time when a star was at maximum altitude you could derive your longitude from the time difference.

Latitude can be worked out from first principals if you know the solistices.
Please explain first principals.
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Old 02-08-2020, 15:15   #35
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Re: wood ships , iron men

The first principals in the derivation of latitude instance would be that an observation of the elevation of the sun when both observer and sun enjoy the same longitude compensated for seasonal factors may be used to derive the observers latitude.
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Old 02-08-2020, 15:38   #36
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Re: wood ships , iron men

Oh yeah, I knew that......
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