Fun Facts
Space runs out of everyday words fast. A proton is about 0.0000000000000017 meters wide; the observable universe is about 880,000,000,000,000,000,000,000,000 meters across. Here's how scientists name numbers that big and that small, and what they do once the names run out.
Type a number in any format, pick a unit if it has one, and see it every way it can be written. Or drag the slider through the powers of ten, from the smallest length in physics to a googol.
Try 93,000,000, 6.02e23, 1.6 x 10^-35, or 10^80.
Real things in space, from the smallest scales in physics to the whole observable universe. Tap any of them to load it into the namer above.
The metric system's trick is that you never need a new unit for a bigger or smaller thing. You keep the meter, the gram, or the second and bolt a prefix onto the front. Each named step past kilo and milli is another factor of 1,000. The International System of Units (SI) now has 24 of them, reaching from 10⁻³⁰ to 10³⁰, a span of 60 powers of ten.
| Prefix | Symbol | Power | Origin | In space |
|---|---|---|---|---|
| quetta2022 | Q | 10³⁰ | Loosely from Latin decem, ten (1000¹⁰) | Jupiter's mass is about 1.9 quettagrams |
| ronna2022 | R | 10²⁷ | Loosely from Latin novem, nine (1000⁹) | Earth's mass is about 6 ronnagrams |
| yotta | Y | 10²⁴ | Latin octo, eight (1000⁸) | The Sun puts out about 383 yottawatts |
| zetta | Z | 10²¹ | Latin septem, seven (1000⁷) | The Milky Way is about 1 zettameter across |
| exa | E | 10¹⁸ | Greek hexa, six (1000⁶) | The Orion Nebula is about 13 exameters away |
| peta | P | 10¹⁵ | Greek penta, five (1000⁵) | One light-year is 9.46 petameters |
| tera | T | 10¹² | Greek teras, monster | Neptune orbits 4.5 terameters from the Sun |
| giga | G | 10⁹ | Greek gigas, giant | Earth orbits about 150 gigameters from the Sun |
| mega | M | 10⁶ | Greek megas, great | Earth's radius is 6.4 megameters |
| kilo | k | 10³ | Greek khilioi, thousand | The ISS flies about 400 km up |
| hecto | h | 10² | Greek hekaton, hundred | Mars's air pressure is about 6 hectopascals; Earth's is 1,013 |
| deca | da | 10¹ | Greek deka, ten | Almost never used in science |
| (none) | 10⁰ | The plain unit | 1 meter, 1 gram, 1 second | |
| deci | d | 10⁻¹ | Latin decimus, tenth | Mostly survives in the decibel |
| centi | c | 10⁻² | Latin centum, hundred | Most shooting stars come from specks smaller than a centimeter |
| milli | m | 10⁻³ | Latin mille, thousand | Millisecond pulsars spin hundreds of times a second |
| micro | µ | 10⁻⁶ | Greek mikros, small | JWST sees infrared light from 0.6 to 28 micrometers |
| nano | n | 10⁻⁹ | Greek nanos, dwarf | Visible light waves are 400–700 nanometers long |
| pico | p | 10⁻¹² | Spanish pico, a small bit | A hydrogen atom is about 100 picometers across |
| femto | f | 10⁻¹⁵ | Danish femten, fifteen | A proton is about 1.7 femtometers wide |
| atto | a | 10⁻¹⁸ | Danish atten, eighteen | LIGO's mirrors moved about 4 attometers for the first gravitational wave |
| zepto | z | 10⁻²¹ | Latin septem, seven | That same wave stretched space by about one part in 10²¹ |
| yocto | y | 10⁻²⁴ | Latin octo, eight | A proton's mass is 1.67 yoctograms |
| ronto2022 | r | 10⁻²⁷ | Mirror of ronna | An electron's mass is about 0.91 rontograms |
| quecto2022 | q | 10⁻³⁰ | Mirror of quetta | A neutrino weighs less than 0.001 quectograms |
A few patterns hide in there. Big prefixes end in -a and small ones end in -o (the older ones like mega and micro predate that rule). Big symbols are capital letters and small ones are lowercase, except kilo, hecto, and deca, which kept their historical lowercase symbols. And the newer names count in thousands: peta and exa are the fifth and sixth powers of 1,000, with a letter dropped from penta and hexa.
One oddity: the base unit of mass is the kilogram, the only SI base unit that already has a prefix built in. Prefixes still attach to the gram, so Earth is 6 ronnagrams, never 6 "yottakilograms."
Prefixes cover 60 powers of ten. Space needs more than that, and scientific notation handles all of them. Every number gets written as a short number between 1 and 10, times ten raised to some power:
6.02E23 or 6.02e23. That "E" means "times ten to the," and has nothing to do with the math constant e (2.718…).The real payoff is arithmetic. Multiplying huge numbers becomes adding exponents. How far does light go in a year? Its speed (about 3 × 10⁸ m/s) times the seconds in a year (about 3.16 × 10⁷): multiply 3 × 3.16 to get about 9.5, add 8 + 7 to get 15, and you have a light-year, 9.5 × 10¹⁵ meters, without ever writing out a zero.
Past a million, the English names split into two systems. The short scale (used in the US and, since 1974, officially in the UK) makes each new name 1,000 times bigger than the last. The long scale (used across much of continental Europe and Latin America) makes each new name a million times bigger, and fills the gaps with "-iard" names.
| Number | Power | Short scale (US, UK) | Long scale (much of Europe) |
|---|---|---|---|
| 1,000,000 | 10⁶ | million | million |
| 1,000,000,000 | 10⁹ | billion | milliard (thousand million) |
| 1,000,000,000,000 | 10¹² | trillion | billion |
| 1,000,000,000,000,000 | 10¹⁵ | quadrillion | billiard |
| 1,000,000,000,000,000,000 | 10¹⁸ | quintillion | trillion |
| 10²¹ | 10²¹ | sextillion | trilliard |
| 10²⁴ | 10²⁴ | septillion | quadrillion |
The long scale is arguably the more logical one: a billion is a million squared (a million, two times), a trillion is a million cubed. The short scale keeps the Latin roots but drops the logic, since its "billion" is 1,000³. Either way, it's a genuine trap: a German article about eine Billion Sterne or a Spanish one about un billón de estrellas means a trillion stars in American English, a thousand times more than an English speaker would guess.
Other languages group digits differently again. India counts in lakh (100,000) and crore (10,000,000). Chinese and Japanese count in groups of four digits: wàn / man is 10,000 and yì / oku is 100,000,000. Powers of ten read the same in every one of them, which is a big part of why science uses them.
The short-scale names follow a rule: take a Latin number n, add "-illion," and you get 10 to the power 3n + 3. So quint (5) gives quintillion, 10¹⁸, and vigint (20) gives vigintillion, 10⁶³. In principle the rule never ends. In practice, almost nobody uses the names past about a trillion, and the ones beyond sound like a joke even when they're correct.
| Name | Power | Something that size |
|---|---|---|
| quintillion | 10¹⁸ | Grains of sand on all of Earth's beaches (roughly 7.5 quintillion, by one popular estimate) |
| sextillion | 10²¹ | Stars in the observable universe: somewhere around 10²² to 10²⁴ |
| septillion | 10²⁴ | Earth's mass in kilograms: about 6 septillion |
| novemdecillion | 10⁶⁰ | The age of the universe in Planck times: about 8 novemdecillion |
| quinvigintillion | 10⁷⁸ | Atoms in the observable universe: about 10⁸⁰, or "100 quinvigintillion" |
| googol | 10¹⁰⁰ | Nothing physical. More than every atom in the observable universe, 100 billion billion times over |
| centillion | 10³⁰³ | The largest name in the standard dictionary list |
The googol was named in 1920 by Milton Sirotta, the 9-year-old nephew of mathematician Edward Kasner, who wanted a word for a 1 followed by 100 zeros. (Google's name is a deliberate misspelling of it.) His follow-up, the googolplex, is 1 followed by a googol zeros. You could never write it out: there are more zeros in it than atoms in the observable universe to write them with.
So what do astronomers actually do? Two things: