The Queen celebrates her actual birthday on 21st April privately, but the occasion is marked publicly by gun salutes in central London. However gun salutes are not fired on Sundays, so as the date falls on a Sunday in 2013, the salute will take place the next day, on Monday 22nd April. In central London there’s a 41 gun salute in Hyde Park at midday (opposite Dorchester hotel) and a 62 gun salute at the Tower of London, at 1pm.
I attended the Hyde Park event accidentally a couple of years ago – i actually thought it was a terrorist event and was relieved to find that it was just a spectacular show of pomp and ceremony by the King’s Troop Royal Horse Artillery.