50 Fun Facts About Compass

On a compass card marked in degrees, how many degrees separate one cardinal direction from the next?

North is 0 and the numbers rise clockwise, so the four cardinal points fall at 0, 90, 180 and 270.

The magnetic compass was first invented in China during which dynasty, initially for divination?

Han dynasty geomancers were using lodestone direction-finders by the 1st century AD, when Wang Chong's Lunheng described one; the compass counts among China's Four Great Inventions.

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

Magnetite, the iron oxide Fe3O4, is the mineral; only a small fraction of it occurs strongly enough magnetised to count as lodestone.

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.

The Middle English word 'lodestone' means what?

Leading stone is the sense: Middle English 'lode' meant a way or course, so a lodestone was the stone that led, a reminder that suspended lodestones were the first compasses.

The early Chinese divination compass was shaped like what, resting on a bronze plate?

A spoon of lodestone, the sinan, rested on a bronze board; the 1st-century Lunheng records that the south-pointing spoon, thrown on the ground, comes to rest pointing south.

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

A fish of thin magnetised iron, the 'south-pointing fish' of the Wujing Zongyao of 1044, floated in a bowl of water to guide troops in gloomy weather or on dark nights.

Which Chinese polymath first explicitly described a magnetised needle compass, in his Dream Pool Essays of 1088?

Shen Kuo, in the Dream Pool Essays of 1088, described rubbing a needle on lodestone and hanging it from a single silk thread, noting that it never settled exactly on due south.

Zhu Yu's Pingzhou Table Talks, dated 1111 to 1117, is notable for being the first text to record what?

Compass use in sea navigation is first recorded there: Zhu Yu wrote that pilots on ships out of Guangzhou watched the stars by night, the sun by day, and the south-pointing needle in overcast weather.

Which English scholar wrote the first European description of the mariner's compass, around 1190?

Alexander Neckam's De naturis rerum, written about 1190, describes sailors using a magnetised needle that turns to show north when the Pole Star is hidden by cloud.

Petrus Peregrinus described both a floating and a dry pivoting compass in 1269 in which famous letter?

Epistola de magnete, his letter of 1269 to a friend, describes a needle floated in a bowl and a pivoted needle in a box with a graduated rim, the first European account of a dry compass.

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

Amalfi, the old maritime republic south of Naples, claims Gioja as a native son; around 1302 he is said to have mounted the needle on a pivot beneath a wind-rose card inside a box.

The earliest Arabic reference to a compass, a needle in a bowl of water, came from which city in 1282?

Cairo is where Baylak al-Qibjaqi wrote his 1282 account of a needle floating in a bowl of water, half a century after the first Islamic mention in a Persian tale collection of 1232.

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

William Gilbert, physician to Elizabeth I, concluded in De Magnete that the Earth is itself a great magnet; he also coined 'electricus' from the Greek word for amber.

What did Gilbert call the spherical lodestone at the centre of his De Magnete experiments?

Terrella, Latin for 'little earth', was Gilbert's name for the lodestone sphere; moving a small needle over its surface, he showed how the needle dipped more steeply toward the poles.

Who demonstrated a rudimentary liquid compass to the Royal Society in 1690?

Edmond Halley showed the Royal Society a needle floating in liquid in 1690; he later charted the Atlantic's compass variation after his Paramore voyages, publishing the map in 1701.

Which American inventor's 1862 patent for an improved liquid marine compass was adopted by the US Navy?

Edward Samuel Ritchie, a Boston instrument maker, patented his liquid compass in 1862; the United States Navy adopted it and it became standard on American warships.

In which year did the Royal Navy generally adopt the liquid compass over Lord Kelvin's dry design?

1908 was when the Royal Navy finally switched, because the recoil of ever-larger guns shook Lord Kelvin's dry-card compasses, while a liquid-filled bowl damped the shock.

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

Declination, which sailors call variation, is the angle between magnetic and true north at a place; charts print it with a date because it shifts year by year.

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

Deviation is the ship's own error; a deviation card, drawn up by swinging the ship through the compass points, lets the navigator convert compass headings into magnetic headings.

What are the two metal spheres mounted either side of a marine compass binnacle for?

Correcting errors caused by the vessel's own steel is their job: the soft-iron spheres, with a vertical Flinders bar and small permanent magnets in the binnacle, cancel the ship's induced magnetism.

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

Lubber line is the fixed mark on the bowl, aligned with the ship's bow, against which the heading is read off the floating card as the gimballed bowl stays level.

Contours on a chart joining points of equal compass variation are called what?

Isogonic lines join points of equal variation, while the special case of zero variation is called the agonic line; the first such chart of the Atlantic was published in 1701.

The traditional European mariner's compass is divided into how many points?

32 points make up the traditional card: the four cardinal, four intercardinal, eight 'half-winds' and sixteen 'by' points; reciting them all in order is called boxing the compass.

How many degrees is one point on the traditional 32-point compass?

11.25 degrees is a point, since 360 divided by 32 gives 11.25; a lookout reporting a ship 'two points off the starboard bow' means 22.5 degrees to the right of dead ahead.

On the mariner's compass, what does 'NE by E' mean?

One point from NE towards E is the reading, 56.25 degrees: in the 'X by Y' names, 'by' always means one point from X stepped in the direction of Y.

The four ordinal or intercardinal directions are which?

NE, SE, SW and NW are the ordinal points, bisecting the cardinal directions at 45, 135, 225 and 315 degrees; with the four cardinals they make the basic eight-wind rose.

Which symbol did the Portuguese cartographer Pedro Reinel introduce as the north mark on compass roses?

The fleur-de-lis first appears as the north mark on Pedro Reinel's charts about 1504, replacing the plain spearhead or arrow that earlier roses used for the tramontana.

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

East was marked with a cross because it pointed towards Jerusalem and the Holy Land, the direction pilgrims and crusaders sailed from Mediterranean ports.

In the traditional Italianate wind names used on old compasses, 'Ponente' is which direction?

West is Ponente, from the Latin for the setting sun; Tramontana is north and Ostro south, with Scirocco and Libeccio among the intermediate winds.

What defined the points of the 32-point 'sidereal' compass rose Arab navigators used before the year 1000?

Rising and setting positions of stars fixed the points: fifteen bright stars each gave a rising and a setting point, thirty in all, with Polaris and its opposite supplying north and south.

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

James Clark Ross, sailing under his uncle John Ross, reached the magnetic pole on 1 June 1831 at Cape Adelaide on the Boothia Peninsula; Amundsen relocated it to a nearby spot in 1904.

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

55 km per year was the 2019 estimate, up from about 9 km a year before 1970; the acceleration forced an early update of the World Magnetic Model in February 2019.

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

The outer core, a shell of liquid iron and nickel some 2,200 km thick, drives the geodynamo; the field's strength at the surface ranges from 25,000 to 65,000 nanotesla.

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

780,000 years is the accepted age of the Brunhes-Matuyama reversal; the record shows about 183 reversals in the last 83 million years, interrupted by 'superchrons' lasting tens of millions of years without one.

Compass needles are 'balanced' for one of how many zones to stop one end dipping at different latitudes?

Five zones are the usual scheme: zone 1 covers most of the Northern Hemisphere and zone 5 Australia and the southern oceans, so a needle bought in Europe may drag in New Zealand; 'global' needles avoid the problem.

Military compasses often divide the circle into how many 'mils'?

6,400 mils make a NATO circle, a rounding of the 6,283 milliradians in a true circle that makes one mil roughly one metre at a kilometre; the Soviet Union used 6,000.

Gunnar Tillander's 1928 transparent baseplate compass was marketed under which brand?

Silva was formed by Tillander and the three Kjellström brothers in the early 1930s; the company sold the baseplate compass to Swedish outdoorsmen and army officers.

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

Orienteering runners strap a thumb compass to the hand holding the map; most have few or no degree markings and exist purely to keep the map oriented to magnetic north.

A gyrocompass has what key advantage over a magnetic compass?

It finds true north because a spinning gyroscope, acted on by the Earth's rotation, settles along the planet's axis; it also ignores nearby iron, which is why steel warships and submarines rely on it.

Who invented the first usable gyrocompass in Germany in 1906?

Hermann Anschütz-Kaempfe built the first usable gyrocompass in Kiel in 1906, and after successful sea trials the German navy adopted it; the American Elmer Sperry patented his own version soon after.

William Austin Burt invented the solar compass in 1835 to solve what problem for surveyors?

Iron ore deposits deflecting magnetic needles made Burt's survey lines unreliable, so his solar compass took its bearing from the sun; in 1844 his needle's wild swings led him to the Negaunee iron range in Michigan's Upper Peninsula.

The 3rd-century Chinese 'south-pointing chariot' kept its figure pointing south by what means?

Gears, with no magnetism, kept the figure's arm steady: the engineer Ma Jun built the first well-documented chariot for the Wei court in the 3rd century, and later versions may have used a differential like a modern car's.

The word 'magnet' may derive from lodestones found in a region of Anatolia called what?

Magnesia, in Anatolia, supplied lodestone to the Greeks, whose 'Magnesian stone' became the Latin magnes and the English magnet.

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

A jewel bearing, usually a synthetic sapphire cup on a hardened steel pin, lets the needle swing almost friction-free; held level, it oscillates for a few seconds before settling along the local magnetic meridian.

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

Secular variation is the slow drift of the field, including the wandering of the magnetic poles; it is why chart compass roses carry a date and an annual rate of change for the variation.

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

A bearing, also called an azimuth, is read through the lensatic or prismatic sight of a card compass; a bearing of 180 means the object lies due south of the observer.

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

A universal sundial combined with a compass let the Damascus astronomer Ibn al-Shatir's 'compass dial' be oriented correctly anywhere to read the hours of the daily prayers.

The planet's field pulls the marked end of a compass needle approximately towards what?

The North Magnetic Pole, the point where the field dips vertically, is what the marked end roughly seeks; because the field is not a perfect dipole, a compass rarely points exactly at it.

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

Thales of Miletus is credited by Aristotle with observing that lodestone attracts iron, and he supposedly reasoned the stone had a soul; the Indian Sushruta Samhita describes using lodestone to draw out embedded arrows.