Parsec: the distance unit that tripped up Star Wars

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Science word of the day: Parsec

Pronunciation: PAHR'-sek

What it means: Ah, the humble parsec, thorn in the side of George Lucas. In 1977, Lucas' "Star Wars: Episode IV ‪—‬ A New Hope" script had Han Solo bragging that the Millennium Falcon completed the Kessel Run in less than 12 parsecs . The problem? Parsecs are a unit of distance, not a unit of time. This has caused angst among Star Wars fans for 49 years and counting.

But when we hit you with this definition, you're going to forgive Lucas for assuming the parsec was some sort of extra-fancy space second. Here it goes: A parsec is a unit of distance required to cause a heliocentric parallax of one arc second. Ouch.

Let's break it down. Heliocentric parallax is a way to measure the distance to a far-off object, such as a star, by measuring how it appears to move in comparison to another distant object (usually another star). An arc second is a fragment of an angle of an arc equal to 1/3600 of a degree.

This means a parsec is a unit of distance that makes a star seem to move 1/3600 of a degree compared with another distant star. It turns out that this equals 206,265 times the distance of Earth to the sun, or 3.26 light-years.

How to use it in a sentence: The 2018 movie "Solo: A Star Wars Story" tries to retcon Han Solo's brag about parsecs by claiming he was talking about distance all along ‪—‬ but we're not sure we're buying it.

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