Posts Tagged ‘units’

PostHeaderIcon Relatable Distances

With this site my goal is to make some of the harder-to-grasp ideas in science easier to handle, so with this episode I wanted to appreciate some distances we have in our lives.

First, we all have heard of feet, meters, inches, kilometers, and most of us have at least heard about light-years, even if we haven’t used them ourselves; however, with light-years, we tend to loose our sense of estimation. It is hard for us humans to fully grasp a light-year, and what about an AU (astronomical unit) or a parsec (parallax arcsecond)? These measurements are employed with our neighbors in space. They describe great lengths across our universe, but what are these measurements?

Length in Kilometre
1parsec 3.0857×10^13km
1light-year 9.461×10^13km
1AU 1.4960×10^8km
1km 1000m
1m 1.0×10^-3km
1 mile 1 kilometre
8 furlongs 10 hectometre
80 chains 100 dekametre
320 rods 1000 metre
8000 links 10,000 decimetre
5280 feet 100,000 centimetre
1760 yards 1,000,000 millimetre

Well, we’ll save how they were derived for a another time. Right now we’ll just focus on sheer distance.

Sorry, for you non-metric users. For a comparative table why I shy away from the Imperial/US system of measures here’s a sample of a mile divided down next to a kilometre.

So, now we know how far these new units, Parsec, AU, and Light-year, are in kilometers. But again, how long are these distances? One Parsec is equal to 30,857,000,000,000 kilometers? Think about what 30 quadrillion feels like in your mind. Roughly 6 million people in the Houston, TX city and surrounding metro areas, about 6.7 billion people living on the whole planet, a certain national debt is around 14.6 trillion dollars… but 30 quadrillion?

If we put some of these units to use we can get a better grasp of their magnitude. Let’s take a simple relationship our Earth and our star, the Sun. The easiest unit to place is an AU, which is one (1) astronomical unit. Well, that may not help too much, so let’s take the Sun, the Earth, and that 1 AU between us and shrink them down. If we shrunk our Earth down to a single grain of sand, the Sun would be almost the size of a DVD disc, and that 1 AU would only be 12.84 yds (about 6.5 people from head to toe.

And how about a Parsec? Well, 1 Parsec is 3.26156 light-year is 3.0857×10^13 km. The nearest star to ours is Proxima Centauri, 4.3 light-years away. Given our micro-scale universe it would be 1983.798 miles away. So you can place your DVD at city hall in Phoenix, AZ and you can put Proxima Centauri on capital hill in Washington, D.C.

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