# How to measure Pluto's diameter?

I have read that a star is chosen from the left hand side of pluto and as pluto moves it blocks the starlight and when the star appears on the right hand side again, meaning it reappears we get the diameter of pluto. Can somebody explain this to me in layman's terms?

• Aside: My first thought was: this will never happen in my lifetime. But it has, more than once. In 2011 both Pluto and Charon occulted the same star. Four days later, Pluto and Hydra occulted a different star. "Anything that can happen, will happen." – garyp Jan 25 '17 at 15:29
• While the occultation method you're asking about was historically important for Pluto, and still important for asteroids, note that since 2015 we have a much more direct measurement of Pluto's size and many other properties. – rob Feb 2 '17 at 4:05

• $5\times 20\,\mathrm{km}$, or in fact at least this since it may not have passed in front of the star centrally. Dimensional analysiscwould have told you this. – tfb Jan 27 '17 at 11:11