90 Fun Facts About Common Sense

How many days are there in a leap year?

February gets a 29th day to keep the calendar in step with the seasons; a person born on it usually celebrates on 1 March otherwise.

How many sides does a standard stop sign have?

The octagon was chosen in 1922 so drivers could recognise it from the back or at night, before signs were reflective.

How many teaspoons make one tablespoon in most countries?

Australia is the odd one out with four teaspoons to the tablespoon.

Which mountain is the tallest in the world when measured from its base rather than from sea level?

Most of the Hawaiian volcano is underwater; its dry prominence beats Everest's 8,849 m above sea level.

How many continents do most English-speaking countries recognise?

From largest to smallest: Asia, Africa, North America, South America, Antarctica, Europe and Australia; other traditions count as few as four.

Roughly what share of people worldwide are right-handed?

Left-handers make up about 10%, which is why so many everyday tools are awkward for them.

How many bones does an adult human skeleton have?

Babies start with about 270, and many fuse together as they grow.

How many strings does a standard violin have?

They are tuned in perfect fifths, G, D, A and E; the earliest pictured violins, around 1530, had only three.

Which is the longest river in the world by most measures?

It carries only about 1% of the Amazon's water, so the Amazon wins on volume.

Which is the largest country in the world by area?

It spans eleven time zones and borders fourteen countries.

Which is the largest and deepest of Earth's five oceans?

It covers about 46% of the planet's water surface, roughly a third of the whole globe.

Botanically speaking, what is a tomato?

It is a fruit eaten as a vegetable; the US Supreme Court still ruled it a vegetable for tariff purposes in 1893.

A peanut is not really a nut. What is it?

It belongs to the pea and bean family and grows its pods underground, which is why Linnaeus named it hypogaea, 'under the earth'.

Which of these fruits is botanically a berry?

Strawberries are aggregate accessory fruits, and the 'seeds' on their outside are each a tiny fruit called an achene.

Which structure is falsely said to be visible to the naked eye from space?

Even from low Earth orbit the wall is hard to make out; you would need to know exactly where to look.

The Canary Islands are named after which animal?

The Latin Canariae Insulae means 'Islands of the Dogs'; the birds were named after the islands, not the other way round.

How many colours did Isaac Newton settle on for the rainbow?

He started with five in 1672, then added orange and indigo to match the seven notes of a musical scale.

Which planet is closest to the Sun?

Despite that, it is only the second-hottest planet, because it has no atmosphere to trap heat.

Which food, properly stored, essentially never spoils?

Its high sugar and acidity stop microbes growing; ancient samples have proved edible, though the 'edible honey in Egyptian tombs' story is itself a myth.

How many hearts does an octopus have?

One main heart circulates blood around the body and two branchial hearts pump it through the gills.

Which is the largest living bird?

It also lays the largest eggs of any land animal and can run at 70 km/h.

Which is the longest bone in the human body?

It is the only bone in the upper leg, and by some measures also the strongest.

Which continent is, on average, the coldest, driest and windiest?

Its annual precipitation is only 1-3 cm, which is why it also counts as the world's largest desert.

A light-year is a unit of what?

It is the distance light travels in a Julian year, about 9.46 trillion kilometres.

Roughly how hot does the air around a lightning bolt get?

That is about five times hotter than the surface of the Sun.

Roughly what fraction of an iceberg is above the water?

Pure ice is about 920 kg per cubic metre against seawater's 1,025, so Archimedes does the rest.

What is the fastest land animal?

Its reliably measured top speed is about 104 km/h; the often-quoted 114 km/h came from a faulty measurement.

Which are the only mammals capable of true, sustained flight?

The others merely glide; vampire bats are also the only mammals that sense infrared.

How many permanent teeth does an adult human normally have?

Children start with 20 baby teeth, which begin appearing around six months of age.

What is the largest organ of the human body?

It makes up roughly 16% of body mass.

Do identical twins have identical fingerprints?

Ridges form around the 15th week in the womb and depend on conditions that are never exactly repeated.

What do the abbreviations a.m. and p.m. stand for?

They are Latin for 'before midday' and 'after midday'.

About how long does sunlight take to reach Earth?

The Sun is about 150 million kilometres away, one astronomical unit.

Why does the Moon always show Earth the same face?

The Moon does rotate, once per orbit, which is exactly why the near side never changes.

What do the interior angles of any triangle add up to?

That is true in flat Euclidean space; on a sphere the total is larger.

How many items are in a baker's dozen?

Bakers reportedly threw in a thirteenth loaf, the 'vantage loaf', when selling a dozen to a retailer.

At what temperature does water freeze on the Fahrenheit scale?

Water boils at 212 °F, so the two points sit exactly 180 degrees apart.

How many letters are in the modern English alphabet?

Five are vowels, nineteen are consonants, and W and Y can act as either.

How many keys does a standard modern piano have?

52 white and 36 black, running from A0 to C8, seven octaves plus a minor third.

How many squares are on a chessboard?

Eight rows by eight columns; a 1283 Spanish manuscript already dismissed 10x10 as too tiresome and 6x6 as too quick.

How many cards are in a standard deck, not counting jokers?

Thirteen ranks in each of four suits: clubs, diamonds, hearts and spades.

How long is a marathon?

That is 42.195 km, named for the legendary run of a messenger from Marathon to Athens.

How many rings are on the Olympic flag?

They represent the inhabited continents, with the Americas counted as one, and are blue, yellow, black, green and red.

How many stripes are on the flag of the United States?

They stand for the thirteen colonies; the fifty stars are the states.

How many arms does a classic snowflake have?

The six-fold symmetry comes from the hexagonal crystal structure of ice, though fewer than 0.1% of flakes are perfectly symmetrical.

How many compartments does a cow's stomach have?

Rumen, reticulum, omasum and abomasum; cows do not have four separate stomachs, despite the saying.

What is a baby kangaroo called?

It is about the size of a lima bean at birth and stays in the pouch for roughly nine months.

How many chambers does the human heart have?

Two atria on top receive blood and two ventricles below pump it out; the whole thing is about the size of a fist.

Which human lung is smaller?

The left has two lobes instead of three because it shares space with the heart.

For daylight saving time, which way do clocks move in spring?

'Spring forward, fall back' is the mnemonic; a New Zealander first proposed shifting clocks by two hours in 1895.

In Roman numerals, what does the letter M stand for?

The seven symbols are I, V, X, L, C, D and M for 1, 5, 10, 50, 100, 500 and 1,000.

Pi is the ratio of a circle's circumference to what?

It comes to about 3.14159; the Greek letter was first used for it by Welsh mathematician William Jones in 1706.

How many feet are in a mile?

Elizabethan England set it at eight furlongs in 1593; it is now exactly 1,609.344 metres.

How many inches are in a foot, and how many feet in a yard?

Since 1959 the foot has been defined as exactly 0.3048 metres.

Why does ice float?

Water expands about 9% when it freezes, so ponds freeze from the top down instead of the bottom up.

Roughly how fast does sound travel in air at room temperature?

That is about 1,235 km/h; it goes more than four times faster through water and fifteen times faster through iron.

Is it truly impossible to sneeze with your eyes open?

The eyelid muscles contract involuntarily, but the reflex can be suppressed.

In the Northern Hemisphere, on which date does the shortest day of the year usually fall?

The Southern Hemisphere's shortest day is around 20 or 21 June.

What happened to Pluto's status in 2006?

The International Astronomical Union redefined 'planet' to exclude it; it remains the ninth-largest object orbiting the Sun.

Which is the largest planet in the Solar System?

It has nearly two and a half times the mass of every other planet combined, and a storm that has raged since at least 1831.

Which planet is less dense than water and would float in a big enough bath?

It is about 30% less dense than water, and has at least 293 known moons.

Which is the hottest planet in the Solar System?

Its thick atmosphere traps heat to about 464 °C, and it spins backwards compared with most planets.

Which mammal lays eggs?

With four species of echidna it makes up the five living monotremes, and the male has a venomous spur on each hind foot.

How many legs does an insect have?

Spiders, with eight, are arachnids, not insects; the word insect comes from Latin for 'cut up', for the three-part body.

Which mosquitoes bite people?

All mosquitoes drink nectar; females of many species also need a blood meal for their eggs to develop.

What are shark skeletons made of?

Some sharks get through 30,000 teeth in a lifetime, replaced conveyor-belt style from a groove inside the jaw.

What colour is a polar bear's skin?

The fur only looks white because the hollow, transparent guard hairs scatter light.

Where do wild penguins live?

The Galapagos penguin nudges just north of the equator; none live in the Arctic.

A koala is not a bear. What is it?

It sleeps up to twenty hours a day and lives almost entirely on eucalyptus leaves.

What colour is a zebra's skin under the stripes?

The coat reads as white with black stripes, but the skin underneath is black.

How long is a goldfish's memory, according to research?

They can tell apart shapes, colours and sounds; the three-second story is a myth.

Which animal cannot stick out its tongue?

A membrane holds the tongue in place; crocodiles do produce tears, but they do not cry.

How many pairs of heart-like 'aortic arches' does an earthworm have?

They sit in segments seven to eleven and pump blood along a closed circulatory system.

How much of a jellyfish's body is water?

The mesoglea, its jelly, is 95% or more water plus collagen; it has no brain.

Which colour did the orange carrot's ancestors most commonly come in?

Dutch growers stabilised the orange 'Long Orange' variety in the 18th century; the night-vision myth was British wartime propaganda to hide radar.

What percentage of a cucumber is water?

Botanically it is a fruit in the same family as melons and pumpkins.

Botanically, a coconut is which of these?

Almonds and cashews are drupes too; the 'nut' is really the seed inside a stony shell.

A mushroom is the fruiting body of what kind of organism?

Its gills drop microscopic spores in a fine rain of powder.

Who is the sandwich named after?

John Montagu, 4th Earl of Sandwich, is credited with the roast-beef original.

The hamburger takes its name from what?

Hamburg gave its name to the dish, which contains no ham.

Who invented the safety pin in 1849, selling the patent for $400?

He is also credited with the lockstitch sewing machine; $400 then is roughly $15,000 today.

What is the 'lead' in a pencil actually made of?

A pure graphite deposit found in Cumbria around 1565 could be sawn into sticks, and the misnomer stuck.

Which Hungarian newspaper editor invented the ballpoint pen after noticing how fast newspaper ink dried?

He filed a British patent in 1938 and fled to Argentina, where the pens are still called 'Birome'.

When the Gregorian calendar was introduced in 1582, how many days were skipped?

Thursday 4 October was followed by Friday 15 October; Britain had to drop 11 days when it switched in 1752.

September comes from the Latin for 'seven', yet it is the ninth month. Why?

October, November and December carry the same off-by-two names for the same reason.

Which invention did Swiss engineer George de Mestral conceive in 1941 after picking burrs off his dog?

He named the hook-and-loop fastener velcro, from the French for velvet and hook.

The Post-it Note grew out of a 3M scientist's 1968 attempt to make what?

Spencer Silver's glue was a failure at being strong, which is exactly what made it useful.

What is the earliest use of paper for hygiene on record?

Purpose-made toilet paper was mass-produced in China by the 14th century; Joseph Gayetty sold the first US commercial version in 1857.

Despite their names, how many toes do all sloths have on each rear limb?

Two-toed sloths simply have two digits on each forelimb; the seven living species split into two distantly related families.

How many toes does a hummingbird have pointing backward on each foot?

Three toes face forward and one, the hallux, faces back; roughly 375 species range from Alaska to Tierra del Fuego.