As the 500 day countdown to the start of the London 2012 Olympic Games begins, the London Organising Committee of the Olympic Games and Paralympic Games (LOCOG) and Omega, Official Timekeeper for the London 2012 Games, today unveiled the Countdown Clock in Trafalgar Square.

The event was attended by LOCOG Chair Seb Coe, Mayor of London Boris Johnson, OMEGA ambassador and world champion heptathlete Jessica Ennis and President of Omega Stephen Urquhart, and the clock will now be counting down to the evening of the 27 July 2012 in days, hours, minutes and seconds.

The Clock was revealed by four Olympic Gold medallists from Team GB – rowers Pete Reed and Andy Hodge and sailors Iain Percy and Andrew Simpson.

The launch of the Countdown Clock is a key moment in the build up to the Olympic and Paralympic Games. It is a reminder for people from across the UK, as well as visitors to the capital, that London will soon be hosting the greatest show on earth.

The design of the Clock reflects the look of the Games. The beams of light on the Clock are inspired by London and its connection with the Meridian line in Greenwich, the home of time. Trafalgar Square was chosen as the setting for the Clock as it is one of London’s most recognisable landmarks and iconic locations, visited by millions of Londoners and tourists each year. It was the centre of celebrations when London won the bid and will once again play a key part in the build-up to the London 2012 Games.

The Clock is made from steel from a Preston-based company. It is 6.5 metres high, 5m long and weighs around 4 tonnes. The Clock took 10 people two days to assemble in the square. The lighting designs on the Clock were created by a British company.

LOCOG Chair Seb Coe said: ‘The launch of the OMEGA Countdown Clock is an important milestone for any Olympic Games and is something of a tradition within the Olympic Movement. It will be a daily and hourly reminder to everyone who visits Trafalgar Square that the countdown to the start of London 2012 has well and truly begun and that the greatest show on earth is soon coming to our country.

‘Athletes’ careers are based on timing and I hope that this milestone moment excites and inspires them to compete at the highest level in 2012. Athletes hoping to compete in the Olympic Games are in the final stretch of their preparation and the next 500 days will be crucial to them as their dream of competing in a Games comes closer to reality.’

Omega’s Stephen Urquhart said that his company is looking forward to returning to London again to time the Olympic Games for the first time in 64 years. He said: ‘In 1948, the last time the Olympic Games were held in this city, Omega was responsible for timing each discipline in every sport. That edition of the Games is remembered for the technological milestones in timekeeping: the photoelectric cell, our fully-automated timing system and the first photofinish camera ever used at an Olympic Games. Then, as now, we were proud to be at the service of the International Olympic Committee and the world’s great athletes.’

Mayor of London Boris Johnson said: ‘The countdown begins right now in the very heart of the capital as we gear up to stage the best Games in living memory and the excitement spreads outwards from Trafalgar Square to every corner of our great city. In 500 days time the atmosphere will be electric as the Olympic cauldron bursts into flames signalling the beginning of the world’s greatest sporting event and London 2012’s glorious legacy unfolds.’

Omega has announced that heptathlete Jessica Ennis has joined its family of brand ambassadors. The 25-year-old British sports star is one of the dominant athletes of her generation having won the World and European Championships in the heptathlon as well as a World Indoor Championship in pentathlon.

She will make her first appearance on behalf of the brand when the Omega Countdown Clock is unveiled in Trafalgar Square on 14^th March. The date will mark 500 days to go before the start of the Games.

Omega President Stephen Urquhart, whose brand will serve as timekeeper at the London 2012 Olympic Games, is excited that Jessica Ennis is now part of an ambassador roster that includes George Clooney, Nicole Kidman and Michael Phelps. He said, "We are delighted that Jessica has joined our family of brand ambassadors. Her accomplishments as a multi-event athlete are so remarkable that it’s hard to believe that she is only 25 years old."

Looking ahead to the next Olympic Games, Stephen Urquhart added, "Jessica’s recent championships confirm that she will be one of the athletes to watch at the London 2012 Olympic Games and we all look forward to watching her compete in her home country."

Jessica Ennis is looking forward to her partnership with Omega. The Sheffield native said, “I am very proud to be joining the Omega family, and am honoured to have the chance to work closely with them as we all continue our journey towards London 2012. Timekeeping is everything in sport. A 1/100^th of a second can be the difference between a gold and silver medal, so OMEGA really is at the service of athletes all over the world”.

Omega’s brand ambassadors are selected from the worlds of fashion, entertainment, sport and adventure. They have been an important part of the Swiss watchmaker’s marketing strategy since 1995 when supermodel Cindy Crawford started working with the brand.

When the London 2012 Olympic Games open in July, Omega will assume its official timekeeping role for the 25^th time. Founded in 1848, the brand has built its reputation on innovative watchmaking and unparalleled performance in accuracy trials. Omega produced the only wristwatch ever to be certified a marine chronometer in 1932 and its Speedmaster watches were worn on the moon in all six lunar missions.