Daily at 1pm a red time ball drops on the Old Observatory to set World Time
It drops at 1pm because the astronomers were busy with their telescopes with the midday sun.
At Greenwich the bright orange time-ball on the observatory roof drops at 1pm every day. It has done this every day since 1833 . 1pm was originally chosen to enable the astronomers to undertake telescopic observations at noon. The tradition is maintained today for the benefit of tourists. NB In summer it drops at 13:00 (1pm) BST or 12:00 (Noon) GMT.
In Washington DC, USA the time-ball was installed in 1845 and dropped every day at noon. It was discontinued and then reinstated for the millennium.