What is a parsec?

Han Solo made the Kessel Run in less than 12 parsecs did he? We think perhaps not – here’s why.

15th December 2017
What is a parsec? © LucasFilm Ltd/Image.net

Han Solo tells Luke Skywalker and Obi-Wan Kenobi that the Millennium Falcon “made the Kessel Run in less than 12 parsecs”. Unfortunately, like the similarly misused ‘light-year’, the parsec is a unit of length, not of time.

A parsec is equal to about 3.26 light-years or roughly 31 trillion kilometres (19 trillion miles). The unit has its origins in one of the first methods of determining the distance to the stars. Using the principle of parallax, some stellar distances can be found by measuring their tiny shift in position as the Earth undergoes its yearly orbit around the Sun. This only works for relatively nearby stars.

One parsec is defined as the distance at which one astronomical unit (the average distance between the Earth and Sun) subtends an angle of one arc-second. The nearest star, Proxima Centauri, is about 1.3 parsecs away, while the Milky Way is more than 31,000 parsecs across. 

 


SFQASubscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.

You are currently reading: What is a parsec? - 15th December