UNITopia: What are these Units?

Written by: Aadarsh Srinivasan

When one usually thinks about units, the definite magnitude of a quantity, they think of the general hall of famers: kilometres (km), liters (L), and kilograms (Kg). But what about the lesser known units, such as a Smoot, the height of Oliver Smoot who is 1.70 meters, or even nanometers over the square root of nanometers? Confused? This article from ScienceRewired will explore the intricate world of funny, crazy, and even cursed units.

First, let’s start with a beard second, which isn’t actually a unit of time, rather a unit of length! It’s the measurement partner of a light year. A beard second is the length an average physicist’s beard grows in one second, which is equivalent to about 5 nanometers. Even though it may not sound like a scientific measurement, it is.

Now, let’s talk about some units that make a little bit more sense but seem to deconstruct with further thought. Here we have 2 common units for gas mileage.

The former is used in Europe, and it tells you how many liters of gas it takes to travel 100 kilometers. Now let’s do some further analysis. We know that 1 liter = 10^-3 meters^3, and 100 kilometres is 10^5 meters, so lets do some simplification.

How did we get square millimetres? Well this is actually found by finding the optimal cross-sectional area of the tube connected to your gas tank so that the tank stays at a constant level when driving. An elegant solution!

Now, another one! The Hubble constant is derived by finding the slope of the best fit line from the data points found by comparing a galaxy’s distance away from earth to the rate (how fast) at which it is moving away from us. This constant is 70 km/s/Mpc. For example, if a galaxy is 10 Mpc away, it is moving away from us at a rate of 700 km/s. Now what is a Mpc? An Mpc is a Megaparsec. Still confused? Allow me to explain.

To find the distance of an object away from us, we point 2 telescopes at the same object, measure the angle between them, and then do some trigonometry to find the distance. What is a parsec, though? A parsec is the distance between two objects if the angle between the 2 telescopes is 1 arcsecond, and the distance between the 2 telescopes is one astronomical unit. Now what is an arcsecond? An arcsecond is 1/3600 of a degree. And an astronomical unit? That is the distance between the earth and the sun!

But how can one find the magnitude of one astronomical unit on earth? It is actually quite simple! You can take one measurement during the winter, and another measurement during the summer, and the resulting distance between the 2 measurements is 2 astronomical units, as the earth is on the opposite side of the sun! So how long is a parsec? It is 1.917 x 10^13 miles, and how many parsecs are in a Megaparsec? One million. Fascinated?

To think, these galaxies are multiple Megaparsecs away from earth.

The universe’s size is truly unfathomable!