Bizarre Measurements

Not all scientific measurements are particularly sensible. Or useful for that matter. Quite a number of them are, well, pretty useless…

attoparsec (apc)
A parsec is an astronomical measurement equal to a little over 30 triillion kilometres. An attoparsec is one quintillionth of a parsec, which is equal to about 3.085 centimetres

Giga ångström (GÅ)
At a ten millionth of a metre, ångströms are used to measure bond lengths in molecules. Most chemical bonds are between 1Å and 3Å. So a Giga ångström would be 10cm.

Light nanosecond
The distance light can travel in a billionth of a second, as it happens, is about 1 foot (30-ish centimetres).

Siriometer
Strangely, I’d never heard of this before. It’s another astronomical measurement equal to one million astronomical units. That works out at around twice the distance from Earth to Sirius (15.813 light years).

YottaWatt (YW)
The amusing sounding YottaWatt is an immense amount of power. Almost a trillion times the amount of power used by the entire human race. The power output of The Sun is roughly 383 YW!

Barn (b)
A barn is a measurement used by nuclear physicists to describe incredibly small areas. 1 Barn is the cross sectional area of a Uranium nucleus. Not useless if you’re a nuclear physicist. Largely meaningless if you’re not.

nanocentury
By a bizarre coincidence, one nanocentury is approximately equal to π seconds.

Exasecond
Doing the opposite thing with units and prefixes, one exasecond is roughly 32 billion years. That’s about 2.3 times the current age of the Universe!

Planck Unit
Planck units are a series of units intended to be the smallest measure of something with any meaning. So the Planck length, for instance, is the smallest length anything that exists could possibly be. I’m not even going to try and say this in an easily comprehensible way. One Planck length is equal to 1.616 252 × 10−35 m. Don’t try thinking about how small that is. It’ll make your brain hurt.

Galactic Year (GY)
Intuitively, a galactic year is the amount of time it takes The Sun to orbit the galaxy once. One GY ago, dinosaurs still ruled the Earth. The Sun, as it happens, is around 20 GY old.

I should really add that some of units certainly aren’t useless. Though if you’re not a physicist, you’ll probably never have any need for them!

About Invader Xan

Molecular astrophysicist, usually found writing frenziedly, staring at the sky, or drinking mojitos.
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14 Responses to Bizarre Measurements

  1. On the other hand, the day is surprisingly variable (thanks to gravitational tugs from the moon and planets). Timing authorities have to regularly throw in leap-seconds to make sure we don’t all go out of sync, though none of us actually notice them. That said, it’s very true that it’s the only inherent measurement of time for us people. I’m sure there’s some way to accurately define a day…
    True enough. But the variation is within a rather narrow range. Well, narrow from the perspective of everyday life, not from the perspective of high-precision science. :-)
    I would imagine that the “Day” in this system would simply be defined in a way that would equal 86,400 SI seconds, the same way that the meter was defined in terms of speed of light in such a way as to be identical to the previous artifact-based definition, hence the rather inconvenient 1/299792458 fraction :-)
    Of course, in a sci-fi setting with aliens, even the day would not be a basic unit, since it’s highly implausible that alien homeworlds would have rotational periods equal to Earth’s. :-) A plank length-based system *might* work if the aliens all happened to share base-10 counting systems (e.g., the basic unit of length could be defined as, say, 10^35 plank lengths), but if they didn’t, even that wouldn’t work …
    Incidentally, in my fictional world, the basic unit of length was originally defined (nowadays, it’s presumably something similar to SI definitions) as twice the distance that an object fell at sea level at the equator in the smallest division of their day (1/216000 of a local day; each unit being 1/60 of the next size up), thus making the standard gravitational acceleration on their planet 1.00, and further confusing mass/weight

  2. invaderxan says:

    Oh, I don’t know. The funny thing is that, even though they’re working backwards, scientists have defined things like the metre to remarkable accuracy using the speed of light. Admittedly 1/299,792,458 is a really cumbersome fraction, but it serves pretty well. Things like seconds are also accurately defined, using radioactive decay (Strontium-88, if I recall correctly).
    On the other hand, the day is surprisingly variable (thanks to gravitational tugs from the moon and planets). Timing authorities have to regularly throw in leap-seconds to make sure we don’t all go out of sync, though none of us actually notice them. That said, it’s very true that it’s the only inherent measurement of time for us people. I’m sure there’s some way to accurately define a day…
    It’s funny… with the possible exception of the planck length, essentially all units are fairly arbitrary. Which is strange to think about…
    And thanks. :)
    (I you can buy t-shirts of it from somewhere actually…)

  3. Thanks. :-) I can’t claim full credit for it, though. I invented it as a reaction to a system I found in a sci-fi book. In this system, the meter was retained from the SI, but the basic unit of time was the “jiffy” equal to the time it takes light to travel 100,000,000 meters. 100,000 “jiffies”, or a bit over 9 hours, made a “shift” and 100 “shifts” made a “month”. I found that rather irrational, as it created a system wherein ones sleep/wake cycle was spread out over 3 “shifts”, and therefore would change every month! One month you might sleep in shifts 1, 4, 7, etc., and then the next in 2, 5, 8, etc. Not to mention that it preserved an essentially arbitrary unit (the meter) while throwing out a natural unit (the day) – and this was a universe that had only humans, so it wasn’t an issue of different aliens with different circadian rhythms making the Earth day arbitrary. It occurred to me that the day was the only truly natural unit for humans, being built into our biology, while the meter is a purely arbitrary unit for humans. Granted, it was originally defined as 1/10,000,000th of the distance from the equator to the north pole, but that’s still Earth-specific and wouldn’t be natural on another world*, nor is it exactly an obvious definition on an ordinary scale.
    *Of course, the same could be said of celsius. It’s only 1/100 of the difference between the freezing and boiling points of water at standard atmosphere, and on a planet with a higher or lower atmospheric pressure – or even at high altitudes on Earth – 1 degree Celsius is no longer 1/100 that difference.
    BTW, I love your icon. :-)

  4. invaderxan says:

    Microdays! I like that. :)
    Fascinating little system you’ve put together there… Logical too.
    (…Oh, and I’m loving the use of decimalisation with the imperial names!)

  5. Light nanosecond
    The distance light can travel in a billionth of a second, as it happens, is about 1 foot (30-ish centimetres).

    That reminds me of a system of measurement I came up with half-seriously.
    The fundamental unit would be the Day (equal to our present day, i.e., 86,400 SI seconds). A light-femtoday, or ~2.59 cm, would be the “New Inch” (thus, the speed of light would, by definition, be 10^15 inches/day). “Foot” would be a semi-official term for 10 New Inches. Smaller units than the day would most often be measured in centidays or millidays if greater precision is needed. (1 cd = a little under 15 minutes; 1 milliday = a little under 1½ minutes). Microdays would be used for very small lengths of time. Then you’d have hectodays in the place of years (I had considered kiloday, but that would be almost 3 years; although a quarter of a kiloday might be useful) and 5-day “weeks”, 20 to a hectoday.
    The “new ounce”, i.e., cubic new inch, would be the basic unit of volume (~17.4 ml or .59 oz). Not sure what the unit of mass would be. Perhaps a certain number of proton-masses or something similar.

  6. invaderxan says:

    Re: Giga Ångstrom
    Hmmm… I think that was actually a typo — why would you ever write 100cm? That’s a metre.
    Thanks for catching that! :)

  7. Anonymous says:

    Giga Ångstrom
    An Ångstrom is ten to the minus ten (10E-10), and Giga is ten to nine (10E9) so a GigaÅngström is obviously 0.1 m or 10 cm. Ångstrom unit would be almost useless if it was the same as athe widely used nanometer, in fact it is one tenth of a nanometer.

  8. invaderxan says:

    Yeah, Barns are funny. So are their subunits — outhouses and sheds. :)
    km/s/Mpc? You’re right, that is quite a juxtaposition. What a bizarre unit…
    (Cosmology was never one of my strong points)

  9. Anonymous says:

    I have always been a great fan of barns. Physicists have a good sense of humor, in general. I also like the units of the Hubble constant .. km per sec per megaparsec, quite a juxtaposition.

  10. invaderxan says:

    I had a feeling you might. ;)
    3.156… Cool. I didn’t bother to calculate it myself. Quite a coincidence really, isn’t it?

  11. invaderxan says:

    I should probably correct that actually. Of course Planck units are important… They’re just impractical to use as actual units unless you’re a particle physicist. :)

  12. ryttu3k says:

    Holy crap, I love these XD And because I’m a nerd, I worked out how long a nanocentury is – as it turns out, 3.15576 seconds, so yeah, pretty damn close to pi!

  13. Planck units are quite fundamentally important. I was asked to derive Planck length in my graduate comprehensive exam (couldn’t quite get it).
    Solving for the age of the Sun in galactic years was a homework problem for me once. Yes, rather useless.
    I’ve never heard of most of those others!

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