Not all scientific measurements are particularly sensible. Or useful for that matter. Quite a number of them are, well, pretty useless…
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.
The distance light can travel in a billionth of a second, as it happens, is about 1 foot (30-ish centimetres).
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).
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!
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.
By a bizarre coincidence, one nanocentury is approximately equal to π seconds.
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 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!