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?

It is counted among China's Four Great Inventions and was adopted for navigation only in the 11th century under the Song.

The earliest Chinese compasses were made from lodestone, a naturally magnetised form of which mineral?

Only a tiny fraction of magnetite is found naturally magnetised.

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

Earth's field, at about half a gauss, is far too weak to do the job on its own.

The Middle English word 'lodestone' means what?

'Lode' once meant a journey or way, a reminder that suspended lodestones were the first compasses.

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

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?

The Wujing Zongyao recommended the iron 'south-pointing fish' for troops caught in gloomy weather or dark nights.

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

He also worked out that the needle points slightly away from true north, an early observation of the compass's offset.

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

Chinese mariners typically floated a magnetised needle in a bowl of water rather than balancing it on a pin.

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

His De naturis rerum describes sailors using a magnetised needle; the Islamic world's first record came in 1232.

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

Dry compasses appear in Europe from about that date and in the Islamic world around 1300.

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

Between 1295 and 1302 he is said to have turned the floating needle into a boxed compass with a 360-degree card.

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

Baylak al-Qibjaqi's account came half a century after the first Islamic mention; a 1300 treatise describes a dry compass used to find the qibla.

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

He also coined the adjective 'electricus' from the Greek word for amber.

What did Gilbert call the spherical lodestone he used as a model Earth?

Cutting it through the poles and equator, he showed how the direction of attraction changes across its surface.

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

He also produced a chart of compass variation for the Atlantic in 1700; a practical liquid compass was patented by Francis Crow in 1813.

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

The Royal Navy later bought his design too, but did not generally adopt liquid compasses until the early 20th century.

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

Growing ship and gun sizes made the liquid design's shock-damping impossible to ignore.

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

Sailors call it variation; where it is zero, the line on a chart is called agonic.

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

A deviation card lets the navigator convert compass headings to magnetic ones; the errors are reduced with two iron balls and a Flinders bar on the binnacle.

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

They work with permanent magnets and a Flinders bar to cancel the effect of ferromagnetic material nearby.

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

The card floats in a gimballed bowl inside a binnacle so it stays level as the ship rolls.

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

Where the variation is zero, the line is called agonic; the value can differ by twenty degrees between the two ends of a single coastline.

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

Each point is 11 and a quarter degrees; reciting them all in order is called 'boxing the compass'.

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

Sailors still speak of an object 'two points off the starboard bow', meaning 22.5 degrees clockwise of dead ahead.

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

The mnemonic is 'X by Y' equals 'one small measure from X towards Y'.

The four ordinal or intercardinal directions are which?

They bisect the cardinal points and together with them form the basic eight-wind rose.

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

Old roses often marked the direction of Jerusalem with a Christian cross.

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

It pointed towards Jerusalem; the traditional wind names for east and north were Levante and Tramontana.

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

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?

Polaris marked the north-south axis and fifteen bright stars supplied the other thirty points.

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

Amundsen found it in a slightly different spot in 1903, and by 2001 it lay off Ellesmere Island.

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

Its rate of travel accelerated sharply after 1970, from about 9 km a year to over 50.

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

The process is called the geodynamo, and the field's surface strength ranges from 25,000 to 65,000 nanotesla.

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

There have been about 183 reversals in the last 83 million years, though the field also has '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?

Zone 1 covers most of the Northern Hemisphere and zone 5 Australia and the southern oceans; 'global' needles avoid the problem.

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

It approximates the milliradian, of which there are 6,283 in a circle; the Soviet Union used 6,000.

Gunnar Tillander's 1928 transparent baseplate compass was marketed by which Swedish company?

Tillander and the three Kjellström brothers formed the company in December 1932 and sold to Swedish outdoorsmen and army officers.

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

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 aligns with the Earth's rotation axis and ignores nearby iron, which is why submarines still use them.

Who invented the first usable gyrocompass in Germany in 1906?

His Kiel company later became Raytheon Anschütz; the American Elmer Sperry patented his own version two years later.

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

He was surveying Michigan's Upper Peninsula, where he later found the great outcrops at Negaunee.

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

Engineer Ma Jun built the first reliably documented one; some may have used differential gears like a modern car.

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

The 6th-century BC philosopher Thales of Miletus made one of the earliest known references to lodestone's pull.

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

Held level, the needle 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?

It is why navigators should use maps with the latest variation figures.

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

Also called an azimuth, it is what lensatic and prismatic sights on card compasses are designed to read precisely.

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

A 1300 treatise by the Egyptian muezzin Ibn Simun had already described a dry compass for finding the qibla.

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

Because the field is not a perfect dipole, compasses generally do not point exactly at either magnetic pole.

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

An ancient Indian medical text, the Sushruta Samhita, describes using lodestone to draw embedded arrows out of the body.