11 teeny units of measurement for tiny things
When someone says they'll be "back in two shakes!" they're probably overpromising...
Hopefully Jansky would be okay with his little — at least in units — legacy.
Hopefully Jansky would be okay with his little — at least in units — legacy. (Bettmann/CORBIS)

here are things in the world that are too small to perceive directly, but that doesn't mean we can't measure them. Here are 11 teeny units of measurement used to describe tiny things.

When someone tells you they'll be "back in two shakes!" they are guaranteed to take much, much longer than that — at least if we're talking shakes in the sense used by physicists. The shake is a unit used to describe the time it takes for one step in a nuclear chain reaction, or 10 billionths of a second.

Even faster than the shake is the jiffy, a unit used to describe the time it takes for light to travel a distance the size of a nucleus. Light takes a little more than a second to travel from the moon to Earth, so to travel the span of a nucleus? Yeah, very fast. The jiffy is also used in other fields, like computer engineering, where it has to do with the computer's clock cycle. But in that case it represents a yawningly slow 10 milliseconds.

A unit of Planck time is how long it takes for light to travel a unit of Planck length. These Planck units were named for the physicist Max Planck, who introduced them in order to provide a way to more simply describe the universe in terms of universal constants. Or something. Let's just say it's useful for quantum physics. A unit of Planck time is a about a sextillion times faster than a jiffy.

Physicists also need ways to measure area, but in the world of atoms, something we think of as tiny might be seen as pretty huge in relative terms. I mean, have you seen a uranium nucleus? Really, if you're looking at nucleuses all day, it's huge! That's why nuclear scientists named its size after a barn. Compared to all those other puny nucleuses, it really is as big as a barn. One barn is 10^(-28) square meters. There's also the megabarn, the kilobarn, the millibarn, the microbarn — also commonly referred to as an "outhouse" — all the way down to the teeny little yoctobarn, also known as a "shed."

The Angstrom, named for physicist Anders Ångström, is a unit of length used for measuring light waves. An Angstrom is one tenth of a nanometer, which is to say one ten-billionth of a meter. The human eye can perceive light in the 4000 to 7000 Angstrom range. Describing the range of electromagnetic radiation in terms of Angstroms really brings home how large the range is and how much of it we can't see. Ultraviolet goes all the way down to 10 Angstroms and infrared goes up to a million.

About 10 years ago, scientists figured out how to weigh things at the attogram level, one attogram being 10^(-18), or a quintillionth, of a gram. A small virus weighs about 10 attograms, much less than a typical bacterium, measurable in comparably giant (10^(-12) gram) picograms.

Named for Henri Becquerel, who, along with the Curies, was awarded the Nobel Prize for work on radiation physics, the becquerel is a measurement of radioactivity. When atoms change and emit particles, the process is called radioactive decay. One becquerel is the radiation of one decay per second. Another unit of measurement for radioactivity is the curie, but a curie represents 37 billion decays per second.

The jansky is a unit used by astronomers to characterize a source of light (or other energy). It was named for physicist Karl Jansky. One jansky is 10^(-26) watts per square meter per hertz. Things in the sky that we can see will have measurements in the thousands of janskys (or millions in the case of the sun), but most of what's out there is only measureable in exceedingly tiny fractions of that, which is why it's useful for astronomers to have the jansky be so small.

Chess programs need a way to measure the relative strength of different moves or players' positions, and this is achieved with centipawns. If you lose a pawn, you are down one pawn, but the cost of that loss is divided into 100 parts for purposes of evaluation. In comparing two possible moves that don't differ by much, a slight advantage for one can be represented by a few centipawns.

The micromort is a unit for measuring the statistical probability of death. One micromort is a one-in-a-million chance of death. Smoking 1.4 cigarettes or spending an hour in a coal mine increase your risk of death by one micromort each. Going skydiving increases it by seven micromorts. You incur 39 micromorts just by living another day. Micromort units can be useful in the insurance industry, but you probably don't want to think about them too much in your day-to-day life.

The Quasihemidemisemiquaver is a British term from musical notation for what Americans boringly call the 128th note. Actually, most people don't call it anything, because it's almost never talked about. Most musical compositions don't have anything higher than a 32nd note, or demisemiquaver, which is about the length of a note in a trill or a fast run. Every once in a while, a run of hemidemisemiquavers, or 64th notes, will show up. But the quasihemidemisemiquaver is rare enough to merit a truly extraordinary 10-syllable name. It's even better if you try to say it to a quasihemidemisemiquaver beat.

Arika Okrent is editor-at-large at and a frequent contributor to Mental Floss. She is the author of In the Land of Invented Languages, a history of the attempt to build a better language. She holds a doctorate in linguistics and a first-level certification in Klingon.



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