Stopping the clock: Ian Westworth, a clock mechanic, checked the inside of Big Ben in London, UK, on Oct 22. He and his team were preparing to stop the 96-meter-tall clock and move its hands, as the UK switched from summer time to winter time, or Greenwich Mean Time (GMT, 格林尼治标准时间). In the UK, such time changes happen twice a year to help people make the best use of daylight in different seasons. This time, the clock stopped from 4 pm on Oct 25 until 2 am the next day, when clocks across the country were turned back to 1 am.