Compasses at Greenwich are about to do something not observed for 360 years

Posted: September 2, 2019 by oldbrew in Geomagnetism, History, solar system dynamics
Tags: ,

Credit: JS Pailly

What a time to be alive says ScienceAlert.
– – –
For the first time in centuries, compasses in Greenwich are about to point directly at true north: an epic coincidence of time and magnetism that hasn’t taken place for some 360 years.

This serendipitous occurrence – which is set to occur within the next fortnight – serves as a startling reminder of how Earth’s magnetic north pole is constantly wandering, unlike the fixed ‘true north’ of Earth’s geographic north pole.

The angular difference between those two different points is called magnetic declination, and while the gap might not be something ordinary people spend a great deal of time thinking about, it’s a disparity that can last for centuries at a time.

For hundreds of years now in the UK, due to Earth’s shifting magnetic north pole, declination has been negative, meaning compass needles have been pointing west of true north.

But nothing lasts forever.

The agonic – an invisible line that connects Earth’s north and south magnetic poles (and which represents zero declination wherever it passes through) – has been moving westward at approximately 20 kilometres (about 12 miles) per year.

At that rate, it’s set to pass through Greenwich this month – the historic site of the Greenwich Royal Observatory – making history in the process.

“At some point in September, the agonic will meet zero longitude at Greenwich,” says geomagnetism researcher Ciaran Beggan from the British Geological Survey (BGS).

“This marks the first time since the Observatory’s creation that the geographic and geomagnetic coordinate systems have coincided at this location.”

As fate would have it, it was a coincidence that when the Royal Observatory was founded in the late 17th century – at the decree of King Charles II – compasses in Greenwich also pointed directly at true north, due to zero declination.

Ever since then, constant variations in the position of Earth’s magnetic north pole due to changes in the composition of Earth’s molten outer core have seen the agonic keep shifting.

It’s a phenomenon that’s expected to endure well past this September’s circumstantial synchronicity (from the perspective of compass users in Greenwich, at least).

Full article here.

  1. Chaeremon says:

    Re: But nothing lasts forever.
    LOL 😉

  2. oldmanK says:

    “nothing lasts forever”, not even the orientation of ‘true north’.

  3. Chaeremon says:

    @oldmanK, re: orientation of ‘true north’

    If it’s true, then it can be found again. So, mark the southernmost and northernmost positions of sun and moon (expect ~3 LNC to pass by). There you have the orientation of big ancient cities found in Mesoamerica.

    The 4 positions draw the corners of a rectangle. This graffiti (with/-out lines for diagonals) appears in many pre-historic “languages”.

  4. Dodgy Geezer says:

    the lines of longitude are about to collapse and strangle us! We’re all going to die!

    Can I have a grant to build a big magnet to correct this?

  5. oldbrew says:

    The direction of travel (blue line) on the declination graphic above is roughly straight from about 1600 to 1800, and again from about 1840 to the present. That leaves us pondering why the declination was nearly fixed between 1800 and 1840, and also for a number of years leading up to 1600.

    The amount of apparent ‘course change’ of the blue line at these dates is quite similar each time.

  6. oldbrew says:

    DG says: Can I have a grant to build a big magnet to correct this?

    Are you Elon Musk in disguise? 😉

  7. cognog2 says:

    Somehow I surmise that this movement of magma must have a considerable influence on the details of the Earth’s climate.

  8. oldbrew says:

    SEPTEMBER 4, 2019
    Mercury’s ancient magnetic field likely evolved over time

    Mercury’s ancient magnetic poles were far from the location of its poles today, implying its magnetic field, like Earth’s, changed over time, a new study says.
    . . .
    The researchers found Mercury’s ancient magnetic poles were far from the planet’s current geographic South Pole and could have changed throughout time, which was unexpected. They expected the poles to be clustering at two points closer to Mercury’s rotational axis at the geographic north and south of the planet. However, the poles were randomly distributed and were all found in the Southern Hemisphere.

    The paleopoles do not align with Mercury’s current magnetic North pole or geographic South, indicating the planet’s dipolar magnetic field has moved. The results reinforce the theory that Mercury’s magnetic evolution was very unlike Earth’s or even other planets in the Solar System. They also suggest the planet may have shifted along its axis, in an event called a true polar wander where the geographic locations of the North and South Poles change.

    Earth has a dipolar field with two poles, but Mercury has a dipolar-quadrupolar one with two poles and a shift in the magnetic equator. Its ancient magnetic field could have looked like either of these, or even been multipolar with “field lines like spaghetti,” according to Oliveira. There is no way to tell without multiple physical rock samples from Mercury, she said. [bold added]

  9. Paul Vaughan says:

    Primer ID √(Φ-φ) U-N

    “the compass may well point east

    Democratic scilensors R C zing day counts.

    U+2309 = U+(1*2*3*5*7*11)-1

    The Nearest Integer Function

    Content tie reza may encode leaves EU won integer step from BRI10’s prime morality:

    360.180290236566 = (491.049532942454)*(207.777451493904) / (491.049532942454 – 207.777451493904)

    4 Shadowing…..

    harmonic of 146.000401793801 nearest 22.1392314983835 is 146.000401793801 / 7 = 20.8572002562573

    ⌊ 146.000401793801 / 22.1392314983835 ⌉ = ⌊6.59464633198586⌉ = 7
    146.000401793801 / 7 = 20.8572002562573

    360.180290236598 = (22.1392314983835)*(20.8572002562573) / (22.1392314983835 – 20.8572002562573)

    …..Up Rocks Summation of Disk Rhymin’ Ant

    “EU say The Party Sove R
    EU mean everything tomb E
    Wi R people so. eager to be soc.rule?
    Ein ever No.when? T00Leave
    Cause wen eye look into Eur. rise
    Well R love shines lie Cuddeye monde mind” — Blue Rodeo

    The left floors bruise the old goat’s right ceiling 4 No.1 rea⌊E-B⌉eaves in 2020 ram man knew Jan.

    29.5 = (⌊1/JEV⌉+⌊1/SEV⌉+⌊1/UEV⌉+⌊1/NEV⌉)/2 = (22+18+10+9)/2 = 59/2

    Queens of th’e a stone age

    232 = 4*(⌊1/JEV⌋+⌊1/SEV⌋+⌊1/UEV⌋+⌊1/NEV⌋)
    232 = 4*(22+18+10+8) = 4*58 = fundamental diskcriminant

    With highly composite clubs play well an 18 whole course on primorial factorization. 4 stability phi mAIayan eyes know peace by piece with no revolution.

  10. oldbrew says:

    Does the magnetic axis have its own spin?

    The Earth’s magnetic poles move. The magnetic North Pole moves in loops of up to 50 miles (80 km) per day. But its actual location, an average of all these loops, is also moving at around 25 miles a year [ref]. In the last 150 years, the pole has wandered a total of about 685 miles (1102 kilometers). The magnetic South Pole moves in a similar fashion. [bold added]

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