50 Fun Facts About Compass

When a phone's compass seems off, Google Maps asks you to move the phone in what shape?

A figure 8 recalibrates the phone's compass: Maps suggests it when your blue dot's beam is wide or points the wrong way, and you repeat it until the beam narrows.

The luopan is a Chinese magnetic compass used in which traditional practice?

Feng shui practitioners use the luopan to find the precise direction of a building, and China first used magnetic compasses for such spiritual purposes rather than for travel.

Lodestone, used in the earliest Chinese compasses, is a natural form of which mineral?

Magnetite is the mineral, and pieces of its naturally magnetised form, lodestone, hung so they could turn, served as the first magnetic compasses.

What is the leading theory for how lodestones become magnetised in nature?

Lightning strikes are the leading explanation: the intense, brief magnetic field around a bolt can magnetise surface ore near the strike, whereas Earth's field, about half a gauss, is far too weak on its own.

What did the name 'lodestone' literally mean when it was coined?

Leading stone is the sense: 'lode' meant a way or course, and the stone got its name from its use by sailors to find their way.

An early Chinese lodestone direction-finder was shaped like what, resting on a smooth bronze plate?

A spoon of lodestone would settle pointing south: early Chinese compasses were read as 'south pointers', unlike today's north-seeking needles.

An 11th-century Chinese military manual describes a direction-finder shaped like what, floating in water?

A fish cut from thin iron was heated red-hot and quenched with its tail pointing north, which magnetised it so that its head pointed south when floated.

Shen Kuo's Dream Pool Essays said a magnetised needle is best hung from a single fibre of what?

Silk, a single fibre fixed to the needle's centre with a dab of wax, held it, and Shen Kuo noted that some needles pointed south and others north.

Zhu Yu's Pingzhou Table Talks says Guangzhou ship pilots relied on the south-pointing needle in which conditions?

In dark weather they turned to the needle, since they steered by the sun by day, and they also hauled up samples of seabed mud to judge where they were.

Europe's earliest known account of the mariner's compass came from Alexander Neckam, who later became what?

An abbot, of Cirencester from 1213; around 1190 he wrote that sailors touched a needle to the lodestone and it whirled until its point faced north.

Besides describing compasses, Petrus Peregrinus's 1269 letter on magnets claimed they could produce what?

Perpetual motion was the promise: he drew a toothed wheel that a lodestone would keep turning forever by alternately pulling and pushing its teeth.

Tradition credits Flavio Gioja, a pilot from which Italian port, with perfecting the mariner's compass?

Amalfi is the town, though Gioja himself may never have existed; the real advance, a needle fixed to a compass card, probably did come from there soon after 1300.

Around 1290, Yemen's sultan al-Ashraf wrote how to use a magnetic compass to find what?

Mecca's direction, the qibla Muslims face in prayer, was his aim, and his treatise is the earliest known evidence of a compass being used to find it.

Which English physician's 1600 book De Magnete argued that the Earth itself is a giant magnet?

William Gilbert showed that Earth's own magnetism turns the needle, overturning older ideas that the Pole Star or a magnetic island drew it.

What name did De Magnete give the lodestone ball it used in its compass-needle experiments?

Terrella, 'little earth', was its name: a needle carried over the ball behaved as a compass does across the globe, persuading the author that Earth is one giant magnet.

In 1692, Edmond Halley explained why compass readings slowly shift by proposing the Earth was what?

Hollow inside was his answer: nested shells, each magnetised and turning at its own rate, would make compass readings drift over the years.

In the 1860s, the first practical liquid-filled ship's compasses redesigned the card to do what?

Take weight off the pivot: a float on the card carried most of it, easing the wear that had made liquid compasses hard to repair, and Edward Samuel Ritchie's floating-card design became a US Navy standard.

Why did Britain's navy give up Lord Kelvin's dry-card compass for liquid-filled ones in the early 1900s?

Shock and vibration easily upset a light dry card while liquid damped its swings, and as warships and their guns grew bigger the liquid design won out.

The angle between the direction a compass needle points and true north at a given place is called what?

Declination, which sailors call variation, changes from place to place, and a walker who ignores it can end up kilometres off course.

On a ship, compass errors caused by iron and steel in the vessel's own structure are known as what?

Deviation became a serious problem once ships were built of iron and steel instead of wood, and any error left after adjustment is logged on a correction card.

Ancient and medieval writers claimed which food could rob a lodestone of its power to attract iron?

Garlic was blamed from ancient times, and the belief was copied for centuries until experiments published around 1600 showed garlic does not stop a lodestone attracting iron.

What is the fixed mark on a ship's compass bowl that shows the heading against the card?

Lubber line takes its name from 'lubber', an old sailors' word for a clumsy novice at sea, as in landlubber.

Chart lines joining places where compasses point equally far off true north are called what?

Isogonic lines appeared on one of the first magnetic charts, drawn after a navy ship sailed the Atlantic measuring how far compass needles pointed off north.

Reciting every compass point in order is called doing what to the compass?

Boxing the compass meant reciting all 32 points in order and then backwards, and the phrase later came to mean a complete reversal of opinion.

Where is a ship reported 'two points off the starboard bow'?

Front right: starboard is the right side, and its old partner larboard gave way to port because the two words sounded confusingly alike.

Every half hour of a watch at sea, a peg went into a compass-marked traverse board to record what?

The heading sailed was pegged every half hour, letting the navigator work out the courses the ship had run by the end of the watch.

The four ordinal or intercardinal directions are which?

NE, SE, SW and NW sit halfway between the cardinal points, but Chinese names them the other way round, so north-east is literally 'east-north'.

Which symbol, still common today, marked north on compass cards from around 1500?

The fleur-de-lis is still the usual north mark, though some early makers fixed the needle slightly off it to suit home waters, which misled sailors farther away.

On old compass roses, which direction was often marked with a Christian cross?

East got the cross because, seen from Europe and the Mediterranean, it pointed towards Jerusalem and the Holy Land.

On old Mediterranean compass roses, the eight main points were named after what?

Winds gave the points their names, so north was marked with a T for Tramontana, the north wind.

Arab navigators of the Indian Ocean fixed the points of their compass rose by what?

Rising and setting positions of stars fixed the points, since each star rises and sets at the same places on the horizon night after night.

Who led the first party to reach the magnetic pole in the Arctic, on the Boothia Peninsula in 1831?

James Clark Ross, serving on his uncle John Ross's expedition, planted the British flag at the magnetic pole he had reached.

As of 2019, the Arctic magnetic pole was drifting from Canada towards Siberia at roughly what speed?

55 km per year was the pace, fast enough that scientists updated the World Magnetic Model, which militaries and airlines navigate by, ahead of schedule.

Earth's magnetic field is generated by convection in molten iron and nickel in which layer?

The outer core is known to be liquid because earthquake shear waves cannot pass through it, while the inner core beneath it is solid.

The Brunhes-Matuyama reversal, Earth's last full magnetic flip, happened roughly how long ago?

780,000 years is the usual estimate, and a compass used before that flip would have pointed south instead of north.

A compass made for use in Europe may misbehave in Australia because its needle does what?

Tilts and drags: compasses are balanced for their home region's magnetic field, so in the wrong zone one end dips and the needle can catch and read falsely.

Military compasses split the circle into 6,400 mils mainly to help what?

Gunnery needs finer angles than whole degrees, so artillery, tank and mortar crews work with almost 18 mils to each degree.

Gunnar Tillander's baseplate compass was sold by which company he co-founded in the early 1930s?

Silva sold it: a clear base with a built-in protractor let walkers set a course straight off a map.

A 'thumb compass' is a minimal, often transparent design used mainly in which activity?

Orienteering racers wear it on the thumb of the hand holding the map, so they can read the map through the clear compass and keep it lined up with north.

Instead of magnetism, a gyrocompass relies on a spinning wheel and what else to find north?

Earth's rotation, combined with gravity, swings the spinning wheel's axis until it settles on true north, the direction of the planet's own axis.

Hermann Anschütz-Kaempfe took up the gyrocompass because he planned to reach the North Pole how?

By submarine, but a magnetic compass would be useless inside a submarine's steel hull, so he turned to a spinning gyroscope instead.

The solar compass William Austin Burt invented in the 1830s became a US government standard for what work?

Surveying public land was its job: the General Land Office made it standard for boundary lines wherever local magnetism threw ordinary compasses off.

Ancient China's 'south-pointing chariot' kept its figure pointing south by what means?

Gears, with no magnetism, turned the figure back against every turn the chariot made, so a pointer set south at the start kept pointing south.

In the Pirates of the Caribbean films, Captain Jack Sparrow's compass points towards what?

What you want most is where it points, which is why Jack gets Elizabeth Swann to use it to find the Dead Man's Chest.

Better compasses mount the needle on what kind of low-friction pivot?

A jewel bearing uses a hard synthetic gem, the same kind found in mechanical watches, so the needle turns with little friction or wear.

What is the term for the slow change in the positions of Earth's magnetic poles over time?

Secular variation adds up over the years, which is why some airports have to renumber their runways, since runway numbers follow compass headings.

A compass reading of the angle, measured clockwise from north, towards a distant object is called what?

A bearing can also point the way back: add or subtract 180 degrees to face the opposite direction, like doing an about-face.

Ibn al-Shatir's 14th-century timekeeping device combined a magnetic compass with what?

A universal sundial shared a small box with the compass, letting Ibn al-Shatir, timekeeper of Damascus's great mosque, work out the times of daily prayers.

A compass needle's north end is drawn to Earth's North Magnetic Pole, which makes that pole what?

A magnetic south pole, since opposite poles attract: it takes the name north from its place on the globe, not from its magnetism.

Which 6th-century BC Greek philosopher was credited with discovering lodestone's attraction to iron?

Thales of Miletus even explained the pull by saying the stone must have a soul, because it could make iron move.