On Second Thought

It's only the 26th time this has happened since 1972, and it may be the last, so enjoy the leap second while you can (which would be at the end of the last minute of June 30). The extra second is being tacked on to correct a slight error made back in the 1960s. John Lowe, of the National Institute of Standards and Technology, explains: "The rate we chose for the atomic clock is slightly wrong. We could have done a little better." Indeed. Why on Earth would anyone calculate a second as being 9,192,631,770 oscillations instead of 9,192,631,950 oscillations? Well, we may be paying for it now. Some are predicting computer-related issues, along the lines of the Y2K scare: http://www.latimes.com/science/la-sci-leap-second-20150110-story.html
   It's all so simple! Scientists use Very Long Baseline Interferometry, employing geometry ~ and quasars as reference points ~ to determine how Earth's radio telescopes are moving relative to one another and over time. And that's how they figure out exactly how long a day is and why we need that extra second every once in a while. It's also not so simple. There are lots of factors, including earthquakes, volcanoes, and oceanic tides, that impact how we roll. “In the short term, leap seconds are not as predictable as everyone would like,” says geophysicist Chopo Ma, of NASA's Goddard Space Flight Center (story, video): http://www.nasa.gov/feature/goddard/nasa-explains-why-june-30-will-get-extra-second