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

Reply
 
LinkBack Thread Tools
post #1 of 26 Old 04-05-2011 Thread Starter
Senior Member
 
dnf777's Avatar
 
Join Date: Jun 2007
Posts: 320
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
 
Local Noon

Does anyone know where within a time zone does the local noon correspond with the clock? Is it half way across the zone? The eastern edge? Or are the lines totally arbitrary and it just falls "somewhere" in the zone?
dnf777 is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 26 Old 04-05-2011
Senior Member
 
AdamLein's Avatar
 
Join Date: Nov 2007
Location: SF Bay area
Posts: 1,917
Thanks: 5
Thanked 6 Times in 5 Posts
Rep Power: 8
 
As with so many questions, the answer is, "It depends."

The extra factor here is the Equation of Time, which is the difference between apparent solar time (what a sundial tells you) and mean solar time (what a sundial would tell you if the sun moved at a constant rate across the sky every day over the course of a year).

If the equation of time is zero, then local apparent solar time is equal to local standard zone time at the standard meridian for that zone. The prime meridian and every 15 degrees of longitude east and west of the prime meridian are standard meridians for the corresponding time zone.

So towards the end of December when the equation of time is zero, and we're not on daylight savings time (the navigator's bane), then at 120 W longitude (the standard meridian in my time zone), it will be local apparent noon when my clock says 12:00.

s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27
AdamLein is offline  
Quote Quick Reply Share with Facebook
post #3 of 26 Old 04-05-2011 Thread Starter
Senior Member
 
dnf777's Avatar
 
Join Date: Jun 2007
Posts: 320
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
 
I always set myself up for those "it depends" answers!

Thanks, that makes sense. I forgot the earth's rotation and revolution aren't perfect circles.
dnf777 is offline  
Quote Quick Reply Share with Facebook
post #4 of 26 Old 04-05-2011
Senior in age only!!!
 
centaursailor's Avatar
 
Join Date: Nov 2010
Location: Balbriggan
Posts: 554
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 5
 
In GMT, 0 degrees, its definitely on the meridian that passes through Greenwich Village, London.
Here in Dublin, 6,15" west, local noon occurs approximately 1225 GMT.

Safe sailing

The great appear great because you are on your knees. James Larkin, Irish Labour Movement.
centaursailor is offline  
Quote Quick Reply Share with Facebook
post #5 of 26 Old 04-06-2011
Senior Member
 
AdamLein's Avatar
 
Join Date: Nov 2007
Location: SF Bay area
Posts: 1,917
Thanks: 5
Thanked 6 Times in 5 Posts
Rep Power: 8
 
Hilariously, the Greenwich meridian has moved several meters since the days of Flamsteed and the founding of the Royal Observatory, so if you go there and stand on the line they have marked, you will actually be in, iirc, a few arcseconds east. The new prime meridian is in the parking lot.

Some say it's a result of a more precise geoid. I subscribe to the "England is tipping over towards Ireland" theory.

s/v Laelia - 1978 Pearson 365 ketch
s/v Essorant - 1972 Catalina 27
AdamLein is offline  
Quote Quick Reply Share with Facebook
post #6 of 26 Old 04-06-2011
Senior Member
 
Boasun's Avatar
 
Join Date: Feb 2007
Location: New Orleans, LA
Posts: 3,070
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 10
   
It is the center of the time zone with seven and a half degrees of Longitude on each side.
But you will need to check with the Nautical Almanac to determine true local noon for that time of the year.

1600 Ton Master, 2nd Mate Unlimited Tonnage

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Maritime Instructor
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Rapture
Boasun is offline  
Quote Quick Reply Share with Facebook
post #7 of 26 Old 04-06-2011
Sunsets and Warm Beer....
 
LandLocked66c's Avatar
 
Join Date: Dec 2009
Location: The Bottom of a Pint Glass...
Posts: 2,111
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
 
So, this has to do with what exactly? Celestial navigation?

1971 23' Oday Pop Top
S/V Frida

You can't steer a boat that isn't moving? Just like a life - P. Lutus
LandLocked66c is offline  
Quote Quick Reply Share with Facebook
post #8 of 26 Old 04-06-2011
Senior in age only!!!
 
centaursailor's Avatar
 
Join Date: Nov 2010
Location: Balbriggan
Posts: 554
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 5
 
Quote:
Originally Posted by AdamLein View Post
Hilariously, the Greenwich meridian has moved several meters since the days of Flamsteed and the founding of the Royal Observatory, so if you go there and stand on the line they have marked, you will actually be in, iirc, a few arcseconds east. The new prime meridian is in the parking lot.

Some say it's a result of a more precise geoid. I subscribe to the "England is tipping over towards Ireland" theory.
Been there in Greenwich and didn,t know it had moved:
That last suggestion is well out of order
Safe sailing

The great appear great because you are on your knees. James Larkin, Irish Labour Movement.
centaursailor is offline  
Quote Quick Reply Share with Facebook
post #9 of 26 Old 04-06-2011
Member
 
Join Date: May 2006
Posts: 30
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
 
Quote:
Originally Posted by LandLocked66c View Post
So, this has to do with what exactly? Celestial navigation?

It has to do with astronomy. Celestial Navigation makes use of it to determine Longitude.

Local Time for any point on the globe is the difference between greenwich time and the local longitude; 4 minutes of time for every degree or 4 seconds of time for every minute of angle. Add for East longitudes, subtract for West longitudes.

Determing Longitude with CN is reciprocal.
Tea-Rex is offline  
Quote Quick Reply Share with Facebook
post #10 of 26 Old 04-06-2011
Sunsets and Warm Beer....
 
LandLocked66c's Avatar
 
Join Date: Dec 2009
Location: The Bottom of a Pint Glass...
Posts: 2,111
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
 
Quote:
Originally Posted by Tea-Rex View Post
It has to do with astronomy. Celestial Navigation makes use of it to determine Longitude.

Local Time for any point on the globe is the difference between greenwich time and the local longitude; 4 minutes of time for every degree or 4 seconds of time for every minute of angle. Add for East longitudes, subtract for West longitudes.

Determing Longitude with CN is reciprocal.
Slightly over my head, very interesting though. Carry on gents!

1971 23' Oday Pop Top
S/V Frida

You can't steer a boat that isn't moving? Just like a life - P. Lutus
LandLocked66c is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
Looking For Local Knowledge San Francisco? PearsonCommander General Discussion (sailing related) 7 02-15-2009 03:03 AM
Re: Some Local Wind Observations NewsReader Mass Bay Sailors 0 03-06-2007 05:15 PM
NY Local Delivery tonylitvak Crew Wanted/Available 3 10-18-2004 04:10 AM

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome