[I am sorry if this isn't the best place for this - it was either here or maybe on the Worldbuilding SE.]
I recently re-read one of my favourite childhood sci-fi books (Chocky by John Wyndham), and in it a young boy is asked by an alien being, where in the Universe our planet is.
It occurred to me that this is almost impossible to describe.
Nowadays, with Wikipedia and the Internet, we can get some of the way by stating that we're in a galaxy that is approximately 10 billion years old, light takes approximately 100000 years to cross it, and which is part of a local group, itself part of a cluster, and that part of a super-cluster.
Unfortunately the alien might then ask a follow-up clarification question such as
what is a year?
So we go to basics - in base 60 (as opposed to binary or base 10), our basic unit of time is called a second, and there are 60 seconds in a minute, 60 minutes in an hour and 24 hours in a day - which is the time our planet takes to rotate once completely. Our planet orbits a local star (that we call the sun) and each complete orbit takes approximately one year, and light takes around 8 minutes to get from our local star to our planet.
Unfortunately our alien might then ask, but how long is a second? - so we then get into atomic clocks, caesium 133 and phases of radiation, followed by the next inevitable question: what is caesium. So we have to get down to the Periodic Table of the Elements and decribe an atom, atomic weight, and how to define caesium in a way that a far off advance civilization could relate to - not to mention perhaps a tangent about Prime Numbers.
So if our alien was lucky enough to be in contact with someone like Professor Brian Cox, or a physyicist with astronomical leanings, how would such a description and conversation go?