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mawingho
Topic Author
Posts: 41
Joined: Sun Jul 22, 2012 4:23 pm

### Isogonic Lines

From Wikipedia http://en.wikipedia.org/wiki/Magnetic_variation

"Magnetic declination is the angle between magnetic north (the direction the north end of a compass needle points) and true north. The declination is positive when the magnetic north is east of true north. The term magnetic variation is a synonym, and is more often used in navigation. Isogonic lines are where the declination has the same value, and the lines where the declination is zero are called agonic lines."

I still do not quite understand the last sentence about Isogonic Lines, anyone knows?

vikkyvik
Posts: 12682
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Isogonic Lines

 Quoting mawingho (Thread starter):Isogonic lines are where the declination has the same value, and the lines where the declination is zero are called agonic lines."

Sounds like isogonic lines are the set of continuous points where the magnetic variation stays constant.

So if you start somewhere with a magnetic variation of, say, +5 degrees, then the line you follow to maintain a magnetic variation of +5 degrees is an isogonic line.

bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

### RE: Isogonic Lines

Agonic lines are simply joining points where the declination is zero ... i.e. no difference between true and magnetic.

A compass will point to true North on this line.

Jimbo

[Edited 2012-08-06 09:54:07]

Mir
Posts: 19491
Joined: Mon Jan 05, 2004 3:55 am

### RE: Isogonic Lines

If you're familiar with contour lines on a map, isogonic lines use the same principle. Just like every point on a contour line has the same altitude, every point on an isogonic line has the same magnetic variation.

-Mir

bond007
Posts: 4428
Joined: Mon Mar 14, 2005 2:07 am

### RE: Isogonic Lines

 Quoting Mir (Reply 3):If you're familiar with contour lines on a map

... or weather of course, showing the pressure with isobars ... iso meaning 'equal'

Jimbo

SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

### RE: Isogonic Lines

isotherms
isotachs
isopleths

Starlionblue
Posts: 20865
Joined: Fri Feb 27, 2004 9:54 pm

### RE: Isogonic Lines

Here's an example of isogonic lines in the United States. As mentioned magnetic variation is the same along the lines.

 Quoting SlamClick (Reply 5): isotherms isotachs isopleths

isohyets.

Rara
Posts: 2310
Joined: Wed Jan 17, 2007 7:41 am

### RE: Isogonic Lines

isobronts

SlamClick
Posts: 9576
Joined: Sun Nov 23, 2003 7:09 am

### RE: Isogonic Lines

isocubes: Line connecting points in a chilled beverage where freezing temperatures occur.

KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

### RE: Isogonic Lines

 Quoting SlamClick (Reply 8):Quoting Rara (Reply 7): isobronts isocubes: Line connecting points in a chilled beverage where freezing temperatures occur.

vikkyvik
Posts: 12682
Joined: Thu Jul 31, 2003 1:58 pm

### RE: Isogonic Lines

isohorny.

i managed to make myself laugh and grimace at the same time with that one.

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