A United Boeing 757-200, registration N41140 performing flight UA-76 from Belfast Aldergrove,NI (UK) to Newark,NJ (USA) with 121 passengers and 9 crew, was climbing out of Aldergrove's runway 07 when the crew stopped the climb at FL100 reporting an unsafe nose gear indication. The crew decided to declare emergency, burn off fuel at FL100, advising that burn off will take about two hours, and to divert to Shannon. The aircraft performed a low approach to Shannon's runway 06 to have the gear inspected from the ground, ground observers reported the nose gear appeared to be in position, the aircraft joined another long approach to runway 06, landed safely and stopped on the runway. The aircraft was towed off the runway.