20 , нужно вставить слова в правильной форме the royal observatory in greenwich, london, is famous for more than just its research into the stars and planets this is the place where the history of accurate time calculation begins. whenever the sun is exactly over a line (called the prime meridian) at the royal observatory, it is precisely midday in the uk. up until fairly recently, all world time (calculate) from this line. though it is an imaginary line circling the earth, it can be physically seen and even (touch) on the courtyard floor of the royal observatory. the royal observatory was established in 1675 in order (solve) a tricky problem. to be able to navigate (they) way around the world, sailors needed to know the exact time in order to pinpoint how far they (travel) and where they were. however, three hundred years ago, most clocks (be/not) that accurate. so the royal observatory gathered together some of the most brilliant scientists in britain to solve the problem and the answer was the prime meridian a fixed point from which all time would be measured. as the meridian goes all the way round the planet, it (divide) the globe into two hemispheres. visitors to the observatory often have their photograph taken (stand) over the line with a foot in each hemisphere. but that is not the only attraction at the royal observatory. it also houses london’s only planetarium as well as the (large) refracting telescope in the uk, plus lots of other exhibits.