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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation > Local Noon
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


Thread: Local Noon Reply to Thread
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Topic Review (Newest First)
04-11-2011 07:37 PM
Flybyknight
Quote:
Originally Posted by LandLocked66c View Post
So, this has to do with what exactly? Celestial navigation?
It has everything to do with Celestial Navigation. Taking a noon site is an example, when determining your longitude.

Dick
04-07-2011 03:18 PM
AdamLein I figured you understood it, I was trying to re-explain it in terms that would make my comments about neighbors/boundaries make more sense.

Am I surprised that boundaries are in dumb places? Not so much.
04-07-2011 03:09 PM
LandLocked66c I understand the time zones. But you guys are loosing me on the boundaries. If you are within a particular timezone, that's what you use. There is a town that straddles OH/IN border. Parts of the town honor daylight savings, other parts don't. Now that causes problems!
04-07-2011 02:43 PM
AdamLein So, imagine you and the guy across the street from you both operate on your own local solar time. Let's say he's due west of you. The sun will pass directly overhead slightly later for him than it does for you, like 0.0001 seconds or something. If you arrange to, I dunno, skeet-shooting together at 3pm, will that affect your plans? Obviously not. Your watches are basically the same.

For most of human history this was fine, since people rarely had interactions with one another at great distances. When they did, it took so long for the communication to happen that you didn't really care what time of day was being discussed.

With industrialization, that changed a little bit. Within a day you could be hundreds of miles away. In a sense, your neighborhood got a bit bigger. You care more about what people 15° west of you are doing, and when they're doing it, than you used to. But for such people, the sun passes overhead 30 minutes later than it does for you. So if you arrange skeet-shooting at 3pm, by the time they show up for it, all the skeets will have been shot.

Putting people into time zones means that even though we might be hundreds of miles apart, our watches say the same thing. So most people in my now-larger neighborhood are operating on the same time as many, so I'm much less likely to have a time-disagreement issue with somebody in my neighborhood.

Unfortunately, if I leave near the edge of a time zone, my neighbors might have clocks set an hour ahead of behind mine, which makes it challenging to arrange get-togethers. So it stands to reason that we might adjust time zones so that their boundaries stay away from populated areas. Note that prior to time zones, this was never an issue.

I'm not sure that time zone boundaries are so adjusted, but it would make sense to do so. I know that the International Date Line zigs and zags for this reason. Who can fathom what went on in the collective mind of the secret committee that set up the modern time zone boundaries?
04-07-2011 02:30 PM
LandLocked66c
Quote:
Originally Posted by AdamLein View Post
Time zones don't solve this problem, the adoption of a convention for what "local" time is used in a given schedule did. In other words in principle we could still have every airline print its schedules solely for the time zone its headquarters is in.

Time zones just reduce the probability that most neighbors will be operating on slightly different times, at the expense of some neighbors operating on radically different times. The borders of time zones were adjusted to decrease the number of the latter kind of neighbor.
God i'm confused!
04-07-2011 11:53 AM
AdamLein
Quote:
Originally Posted by svHyLyte View Post
A train scheduled to arrive in Denver as 12:00 always presented the question of where 12:00 was taken. At the destination? At the point of departure? Halfway between the two?
Time zones don't solve this problem, the adoption of a convention for what "local" time is used in a given schedule did. In other words in principle we could still have every airline print its schedules solely for the time zone its headquarters is in.

Time zones just reduce the probability that most neighbors will be operating on slightly different times, at the expense of some neighbors operating on radically different times. The borders of time zones were adjusted to decrease the number of the latter kind of neighbor.
04-07-2011 10:28 AM
lapworth
Quote:
Originally Posted by LandLocked66c View Post
I have a cheapy sextant, it is fun! I just don't feel like I can apply alot of the information. Seems like it's one of those things that if you aren't using it everyday it's difficult to retain the knowledge.
Your finger tips are about 5 degrees which is about 20 min. Next time you watch the sunset see how many fingers you place between the horizon and the sun multiple by 20 that's how much daylight is left. Now if you know what time the sunsets you can figure the time.
04-07-2011 09:28 AM
Boasun World's Time zones can be determined by taking your longitude and divide it by 15. The resultant answer is the time zone you are in. And it is either plus or minus, pending on whether you are East or West of the Prime meridian.
04-07-2011 08:52 AM
svHyLyte
Quote:
Originally Posted by Boasun View Post
Actually for those of you who have nothing to do with Navigation... The time zones of most countries are determined by the fifteen degree Longitude for their areas. Some time zones are slid one way or another due to political stupidity, but there is nothing I can do about that.
Well it really has nothing to do with political stupidity (tho' there's certainly no shortage of that!). Time zones were agreed upon in the age of steam (trains) as a matter of allowing train operators to set train schedules. (Pre-time zones, locales set their watches/clocks by local apparent noon. A train scheduled to arrive in Denver as 12:00 always presented the question of where 12:00 was taken. At the destination? At the point of departure? Halfway between the two?) Zone lines/times were adjusted to account for matters such as the difficulty of having a portion of a city in one zone and the rest in another, eg Corpus Christi, Tx at 97º 30.00' W

FWIW...
04-06-2011 06:36 PM
LandLocked66c
Quote:
Originally Posted by dnf777 View Post
ps....66c: if you want something to occupy even more spare time, I highly recommend a cheap, Davis Mark III sextant. I've only had mine a week, shot readings in my yard, and already want a better one! Lots of fun and learning.
I have a cheapy sextant, it is fun! I just don't feel like I can apply alot of the information. Seems like it's one of those things that if you aren't using it everyday it's difficult to retain the knowledge.
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