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.
几个世纪以来，格林威治的罗盘第一次将指向真北:一个360年来从未发生过的时间和磁场的史诗般的巧合。
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.
这一意外事件——预计将在未来两周内发生——令人吃惊地提醒人们，地球的磁北极与地球地理北极固定的“真北极”不同，是如何不断地漂移的。
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.
这两个不同点之间的角差被称为磁偏角，虽然这种差距可能不是普通人花大量时间思考的问题，但这种差距一次可以持续数百年。
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.
几百年来，由于地球磁极的移动，英国的磁偏角一直是负的，这意味着指南针一直指向正北的西面。
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.
但没有什么是永恒的。条不可见的线连接着地球的南北磁极(在它经过的任何地方都代表零赤纬)，一直以每年约20公里(约12英里)的速度向西移动。
(British Geological Survey/Twitter)
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.
按照这个速度，它将于本月通过格林威治——格林威治皇家天文台的历史遗址——在这个过程中创造历史。
"At some point in September, the agonic will meet zero longitude at Greenwich," says geomagnetism researcher Ciaran Beggan from the British Geological Survey (BGS).
英国地质调查局(BGS)的地磁研究人员西兰·贝根(Ciaran Beggan)说：“在9月份的某个时候，阿戈尼奇将在格林威治遭遇零经度。”
"This marks the first time since the Observatory's creation that the geographic and geomagnetic coordinate systems have coincided at this location."
“这标志着自天文台成立以来，地理和地磁坐标系首次在这个位置重合。”
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.
巧合的是，当皇家天文台在17世纪晚期根据查理二世国王的命令建立时，格林威治的罗盘也由于零赤纬而直接指向真北。
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.
从那时起，由于地球熔化的外核成分的变化，地球磁北极的位置不断变化，导致了电子的不断移动。
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).
这种现象预计将在今年9月的间接同步之后继续存在(至少从格林威治罗盘用户的角度来看)。
"By 2040, all compasses will probably point eastwards of true north."
“到2040年，所有圆规都可能指向正北的东方。”
As for the more distant future beyond that, scientists' ability to foresee the magnetic movements are limited.
至于更遥远的未来，科学家们预测磁场运动的能力是有限的。
"It is, at present, impossible to predict how the magnetic field will change over decades to centuries," Beggan says, "so the compass may well point east of true north for another 360 years in the UK."
贝根说:“目前还无法预测磁场将如何在几十年到几百年的时间里发生变化。因此，在未来360年里，英国的罗盘很可能指向正北以东。”
