I don’t understand it enough to explain it, actually I don’t really understand it myself at all
In: Physics
A parsec is ~3.26 lightyears, which is the distance light can travel in the vacuum of space (~6 trillion miles).
Why is a parsec such an odd number? I assume this is what you’re struggling with. Draw a large dot on a piece of paper. That’s the sun. Draw a line straight up from the sun. Now draw a smaller dot next to the sun. This is the earth. Assuming the distance between the sun and the earth is at average, this is your starting point. Now draw a short line from the earth thats parallel with the line from the sun. This is degree 0. Now draw a line from the same starting point, but at 1/3600 of a degree (an arc second) leaning toward the sun. (You can draw any angle. This isn’t to scale). Where the angled earth line and the straight sun lines meet is one parsec from the sun.
The reason this is so complicated is because from where we are on earth, the easiest way to measure the distance between earth and another celestial body is parallax. We know how far earth is from the sun. We know when the earth is at any specific point in its orbit around the sun. Using the diameter of the earth’s orbit, and the distance a celestial body appears to move in our sky between these two points can be used to calculate how far away it is.
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