What is declination?

[David Brooks]

What is declination? I had to look it up after it was mentioned by Steve
Carroll!

https://www.usgs.gov/faqs/what-declination

At most places on the Earth's surface, the compass doesn't point exactly
toward geographic north. The deviation of the compass from true north is
an angle called "declination" (or "magnetic declination"). It is a
quantity that has been a nuisance to navigators for centuries,
especially since it varies with both geographic location and time. It
might surprise you to know that at very high latitudes, the compass can
even point south!

The collar of USGS topographic maps shows the magnetic declination at
the center of the map the year that the map was made. That's important
information for anyone who is using the map and a compass to navigate.
NOAA has an online calculator for estimating the declination at any
longitude/latitude on a specific date.

Declination is simply a manifestation of the complexity of the
geomagnetic field. The field is not perfectly symmetrical; it has
non-dipolar "ingredients," and the dipole itself is not perfectly
aligned with the rotational axis of the Earth. If you were to stand at
the north geomagnetic pole, your compass, held horizontally as usual,
would not have a preference to point in any particular direction, and
the same would be true if you were standing at the south geomagnetic
pole. If you were to hold your compass on its side, the north-pointing
end of the compass would point down at the north geomagnetic pole, and
it would point up at the south geomagnetic pole.

The USGS Geomagnetism Program operates magnetic observatories in more
than a dozen locations around the United States.

=

Did I know this and have simply forgotten?
I'm a little perturbed by this discovery. :-(

[FromTheRafters]

Post by David Brooks
What is declination? I had to look it up after it was mentioned by Steve
Carroll!
https://www.usgs.gov/faqs/what-declination
At most places on the Earth's surface, the compass doesn't point exactly
toward geographic north. The deviation of the compass from true north is an
angle called "declination" (or "magnetic declination"). It is a quantity that
has been a nuisance to navigators for centuries, especially since it varies
with both geographic location and time. It might surprise you to know that at
very high latitudes, the compass can even point south!
The collar of USGS topographic maps shows the magnetic declination at the
center of the map the year that the map was made. That's important
information for anyone who is using the map and a compass to navigate. NOAA
has an online calculator for estimating the declination at any
longitude/latitude on a specific date.
Declination is simply a manifestation of the complexity of the geomagnetic
field. The field is not perfectly symmetrical; it has non-dipolar
"ingredients," and the dipole itself is not perfectly aligned with the
rotational axis of the Earth. If you were to stand at the north geomagnetic
pole, your compass, held horizontally as usual, would not have a preference
to point in any particular direction, and the same would be true if you were
standing at the south geomagnetic pole. If you were to hold your compass on
its side, the north-pointing end of the compass would point down at the north
geomagnetic pole, and it would point up at the south geomagnetic pole.
The USGS Geomagnetism Program operates magnetic observatories in more than a
dozen locations around the United States.
=
Did I know this and have simply forgotten?
I'm a little perturbed by this discovery. :-(

Don't worry, I think it is they whom are confused. I always learned
that 'declination' was 'dip' and deviation was as described above.

https://skybrary.aero/articles/magnetic-dip

[Steve Carroll]

Post by FromTheRafters

Post by David Brooks
What is declination? I had to look it up after it was mentioned by Steve
Carroll!
https://www.usgs.gov/faqs/what-declination
At most places on the Earth's surface, the compass doesn't point exactly
toward geographic north. The deviation of the compass from true north is an
angle called "declination" (or "magnetic declination"). It is a quantity that
has been a nuisance to navigators for centuries, especially since it varies
with both geographic location and time. It might surprise you to know that at
very high latitudes, the compass can even point south!
The collar of USGS topographic maps shows the magnetic declination at the
center of the map the year that the map was made. That's important
information for anyone who is using the map and a compass to navigate. NOAA
has an online calculator for estimating the declination at any
longitude/latitude on a specific date

... because magnetic north 'moves' over time ("polar wandering").

Another, lesser issue, is factoring in 'grid north', which exists due to
how maps are created (projection). And then there are user error related
issues, one that people often forget about is: a magnet can be affected
by its surroundings. I once took a reading on some granite that was
covered with dirt and didn't realize how that rock was trashing the
reading. The granite itself isn't an issue as it's not magnetic, but it
can have traces of things that are magnetic.

Post by FromTheRafters

Post by David Brooks
Declination is simply a manifestation of the complexity of the geomagnetic
field. The field is not perfectly symmetrical; it has non-dipolar
"ingredients," and the dipole itself is not perfectly aligned with the
rotational axis of the Earth. If you were to stand at the north geomagnetic
pole, your compass, held horizontally as usual, would not have a preference
to point in any particular direction, and the same would be true if you were
standing at the south geomagnetic pole. If you were to hold your compass on
its side, the north-pointing end of the compass would point down at the north
geomagnetic pole, and it would point up at the south geomagnetic pole.
The USGS Geomagnetism Program operates magnetic observatories in more than a
dozen locations around the United States.
=
Did I know this and have simply forgotten?
I'm a little perturbed by this discovery. :-(

Don't worry, I think it is they whom are confused. I always learned
that 'declination' was 'dip' and deviation was as described above.
https://skybrary.aero/articles/magnetic-dip

Declination is the proper term here:

"Magnetic declination (also called magnetic variation) is the angle
between magnetic north and true north at a particular location on the
Earth's surface. The angle can change over time due to polar wandering."

--

"Magnetic declination should not be confused with magnetic inclination,
also known as magnetic dip, which is the angle that the Earth's magnetic
field lines make with the downward side of the horizontal plane.Magnetic
declination should not be confused with magnetic inclination, also known
as magnetic dip, which is the angle that the Earth's magnetic field
lines make with the downward side of the horizontal plane."

--

"The term magnetic deviation is sometimes used loosely to mean the same
as magnetic declination, but more correctly it refers to the error in a
compass reading induced by nearby metallic objects, such as iron on
board a ship or aircraft."

<https://en.wikipedia.org/wiki/Magnetic_declination>

(wikipedia has it right this time)

[FromTheRafters]

Post by Steve Carroll

Post by FromTheRafters

Post by David Brooks
What is declination? I had to look it up after it was mentioned by Steve
Carroll!
https://www.usgs.gov/faqs/what-declination
At most places on the Earth's surface, the compass doesn't point exactly
toward geographic north. The deviation of the compass from true north is an
angle called "declination" (or "magnetic declination"). It is a quantity
that has been a nuisance to navigators for centuries, especially since it
varies with both geographic location and time. It might surprise you to
know that at very high latitudes, the compass can even point south!
The collar of USGS topographic maps shows the magnetic declination at the
center of the map the year that the map was made. That's important
information for anyone who is using the map and a compass to navigate. NOAA
has an online calculator for estimating the declination at any
longitude/latitude on a specific date

... because magnetic north 'moves' over time ("polar wandering").
Another, lesser issue, is factoring in 'grid north', which exists due to
how maps are created (projection). And then there are user error related
issues, one that people often forget about is: a magnet can be affected
by its surroundings. I once took a reading on some granite that was
covered with dirt and didn't realize how that rock was trashing the
reading. The granite itself isn't an issue as it's not magnetic, but it
can have traces of things that are magnetic.

Post by FromTheRafters

Post by David Brooks
Declination is simply a manifestation of the complexity of the geomagnetic
field. The field is not perfectly symmetrical; it has non-dipolar
"ingredients," and the dipole itself is not perfectly aligned with the
rotational axis of the Earth. If you were to stand at the north geomagnetic
pole, your compass, held horizontally as usual, would not have a preference
to point in any particular direction, and the same would be true if you
were standing at the south geomagnetic pole. If you were to hold your
compass on its side, the north-pointing end of the compass would point
down at the north geomagnetic pole, and it would point up at the south
geomagnetic pole.
The USGS Geomagnetism Program operates magnetic observatories in more than
a dozen locations around the United States.
=
Did I know this and have simply forgotten?
I'm a little perturbed by this discovery. :-(

Don't worry, I think it is they whom are confused. I always learned
that 'declination' was 'dip' and deviation was as described above.
https://skybrary.aero/articles/magnetic-dip

"Magnetic declination (also called magnetic variation) is the angle
between magnetic north and true north at a particular location on the
Earth's surface. The angle can change over time due to polar wandering."
--
"Magnetic declination should not be confused with magnetic inclination,
also known as magnetic dip, which is the angle that the Earth's magnetic
field lines make with the downward side of the horizontal plane.Magnetic
declination should not be confused with magnetic inclination, also known
as magnetic dip, which is the angle that the Earth's magnetic field
lines make with the downward side of the horizontal plane."

Upon further reading, I was confusing 'inclination' with 'declination'.

[Steve Carroll]

Post by FromTheRafters
Upon further reading, I was confusing 'inclination' with 'declination'.

This is an argument that is apparently 'going around'... much like the
ones about azimuth, bearing and a couple of other terms. Whatever we
choose to call it, if we don't factor it into our navigation, we're
fucked ;)

Backpackers in the UK have it easy, they really don't need to mess with
it. Mine is such that if I don't account for it, a mile traveled can be
approximately 1/4 mile off course!

[Mike Easter]

Post by FromTheRafters
Don't worry, I think it is they whom are confused. I always learned
that 'declination' was 'dip' and deviation was as described above.
https://skybrary.aero/articles/magnetic-dip

I agree that 'declination' as used for magnetic variation is a
/mistake/; altho' the wp main article makes the same error.

Fortunately (by some metric) one of the 'beauties' of the wp is that
people can have their say in the Talk section of the article and take it
to task.

Post by FromTheRafters
This page is badly written, very amateurish, verbose and confusing,
it badly needs to be re-written. Frankly, the term 'Magnetic
Declination' is a misnomer in itself. It should be Magnetic
Variation. This removes a whole layer of confusion. Magnetic
Deviation could then be explained perhaps as an adjunct in relation
to compasses mounted on vehicles etc.

There /IS/ such a thing as magnetic 'declination' (or dip) as regards
aviation compasses.

I particularly agree w/ this sentence from a different par in the Talk

Post by FromTheRafters
The term declination is more often used with regard to some specific
vertical angles.

The 'verticalness' of declination (as in decline) is essential, because

Post by FromTheRafters
In astronomy, declination (abbreviated dec; symbol δ) is one of the
two angles that locate a point on the celestial sphere in the
equatorial coordinate system, the other being hour angle.
The root of the word declination (Latin, declinatio) means "a bending
away" or "a bending down". It comes from the same root as the words
incline ("bend forward") and recline ("bend backward").

From the 'general' wp article on declination, not magnetic declination
which is a mess.

[Steve Carroll]

Post by Mike Easter

Post by FromTheRafters
Don't worry, I think it is they whom are confused. I always learned
that 'declination' was 'dip' and deviation was as described above.
https://skybrary.aero/articles/magnetic-dip

I agree that 'declination' as used for magnetic variation is a
/mistake/; altho' the wp main article makes the same error.

I've not been around as long as you two so maybe the term has been
'hijacked'. I've always heard of what I'm talking about described as
declination. In any event, when I use the term it means the difference
between magnetic north and true (and/or grid) north.

[FromTheRafters]

Post by Steve Carroll

Post by Mike Easter

Post by FromTheRafters
Don't worry, I think it is they whom are confused. I always learned
that 'declination' was 'dip' and deviation was as described above.
https://skybrary.aero/articles/magnetic-dip

I agree that 'declination' as used for magnetic variation is a
/mistake/; altho' the wp main article makes the same error.

I've not been around as long as you two so maybe the term has been
'hijacked'. I've always heard of what I'm talking about described as
declination. In any event, when I use the term it means the difference
between magnetic north and true (and/or grid) north.

Yes, it is like 'depreciation' where the misunderstanding of the
difference between physical depreciation and economic depreciation get
used by car salesmen to confuse a buyer into buying something he
shouldn't. Why they can legally call market value fluctuations a
depreciation when it can also increase is beyond me.

[Mike Easter]

Post by Steve Carroll

Post by Mike Easter
I agree that 'declination' as used for magnetic variation is a
/mistake/; altho' the wp main article makes the same error.

I've not been around as long as you two so maybe the term has been
'hijacked'. I've always heard of what I'm talking about described as
declination. In any event, when I use the term it means the difference
between magnetic north and true (and/or grid) north.

I 'don't like it' when terms get 'bent' around so that their 'meaning'
depends on the context, and then some context becomes sufficiently
'popular' that 'authorities' begin to say what the term 'has now' come
to mean.

The most horrible example being the 'kilo-'prefix which some people
believe can mean 1000 or 1024. That is ridiculous.

Some other people HATE the introduction of 'neologisms' even when the
neo is far better than the 'bastardization' of a term it is better than,
call it my 'favorite' neo, kibi- and the rest of its entire family of
'-bi/s'

In any case, my 'life experiences' with magnetic north and true north
and their adjustments have almost entirely been w/ aviation, and my
personal aviation has nothing to do w/ GPS; that wasn't available to
'us' in my private flying days.

The term 'declination' was never heard of. Didn't exist in that
context. We had to adjust to magnetic variation all the time as our
airplane had a magnetic compass and we had to fly 'a heading' based on
corrections for wind and magnetic variation.

[Mike Easter]

Post by Mike Easter
The most horrible example being the 'kilo-'prefix which some people
believe can mean 1000 or 1024. That is ridiculous.

I can be persuaded to accept this .ca 'dissection' of the divergent uses
of the terms declination and variation, so that I don't bristle at the
use of declination as much as I do the misuse of the kilo term.

Post by Mike Easter
Both declination and variation are used to describe the angle between
magnetic north and true north. The term deviation is also used from
time to time. Here is an explanation of the differences between the
three terms.
Declination
This is the term preferred by those who study the magnetic field; it
is also the term most commonly used by land navigators. Sometimes the
term "magnetic declination" is used.
Variation
This term is preferred by mariners and pilots because the word
"declination" also has an astronomical usage - the angle of a star or
planet above the celestial equator. However, the word "variation" is
used by geomagneticians to refer to time changes in the magnetic
field.
Deviation
In a vehicle such as a ship or aircraft, a compass is influenced by
the magnetism of the iron used in the construction of the vehicle as
well as the Earth's magnetic field. This causes the compass needle to
point in the wrong direction. This directional error is called
"deviation". Many people incorrectly use deviation when they mean
declination.

[FromTheRafters]

Post by Mike Easter

The most horrible example being the 'kilo-'prefix which some people believe
can mean 1000 or 1024. That is ridiculous.

I can be persuaded to accept this .ca 'dissection' of the divergent uses
of the terms declination and variation, so that I don't bristle at the
use of declination as much as I do the misuse of the kilo term.

Both declination and variation are used to describe the angle between
magnetic north and true north. The term deviation is also used from
time to time. Here is an explanation of the differences between the
three terms.
Declination
This is the term preferred by those who study the magnetic field; it
is also the term most commonly used by land navigators. Sometimes the
term "magnetic declination" is used.
Variation
This term is preferred by mariners and pilots because the word
"declination" also has an astronomical usage - the angle of a star or
planet above the celestial equator. However, the word "variation" is
used by geomagneticians to refer to time changes in the magnetic
field.
Deviation
In a vehicle such as a ship or aircraft, a compass is influenced by
the magnetism of the iron used in the construction of the vehicle as
well as the Earth's magnetic field. This causes the compass needle to
point in the wrong direction. This directional error is called
"deviation". Many people incorrectly use deviation when they mean
declination.

Thanks Mike, that sort of explains how inclination and declination
became different but not opposite.