Cosmic Measurements

I know you've heard the words,"parsec, light year, and AU". Have you ever wondered what the heck they were talking about? Well, here are a few spatial measurements and hopefully I can explain them in layman's terms.

 Let's start with an easy one:

Light Year- is the distance that light can travel in a year or; 186242 mile per second. That is fast! As a matter of fact, it is the universe's speed limit; nothing goes any faster, but many things go as fast. photons, radio waves, and gamma bursts to name a few.

OK, when you look at the sunshine consider that the light you see left the Sun eight  minutes ago. The Sun is 93 million miles away; at the speed of light it takes those light photons that long to leave the sun, race through space, and bounce off your retina.

Get the picture?

Now let's talk about an AU:

AU stands for 'astranomical unit.' Actually this one may be easier to explain than a light year. An AU is 93 million miles(the distance from the Sun to the Earth). It gives perspective to the other planets in relation to the Earth. Example:  Mars is roughly 2 AUs from the Sun, Jupiter is 6 AUs from the Sun(or 5AU from Earth), and Saturn is 12 AUs from the Sun, etc.,etc. 

OK, now let's do a parsec:

In Star Wars Han Solo bragged that the Millennium Falcon could speed through space at several 'parsecs', this is the only real blatant mistake made in the first movie. A parsec is a measurement of distance, not speed. But, how would Han know this?  He was only a space merchant and reluctant rebel.

Back to reality.

The parsec is equal to the length of the adjacent side of an imaginary right triangle in space. The two dimensions on which this triangle is based are the angle (which is defined as 1 arcsecond), and the opposite side (which is defined as 1 Astronomical Unit -distance from the Earth to the sun). Using these two measurements, along with the rules of trigonometry, the length of the adjacent side (the parsec) can be found.
It is about 3.26 light-years, or just under 31 trillion (3.1×10¹³) kilometres (about 19 trillion miles).

The parallax method is the fundamental calibration step for distance determination in astrophysics.

Here is a graph.

 German astronomer Friedrich Wilhelm Bessel in 1838, first used this approach to calculate the distance of 61 Cygni.^[3]

That's not that hard to grasp, now is it?