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Monday, March 14, 2011

Daylight Savings Time - Set your clocks ahead 1 hour + 1.8 microseconds

alarm clock, bought from IKEAImage via WikipediaDaylight savings time began today, Sunday, in the US. Set your clocks ahead 1 hour. Daylight savings time doesn't begin in Israel until April 1, so for the remainder of March the East Coast of the US will be just 6 hours ahead of Israel, instead of 7. Here is a list of the commencement of daylight savings times around the world. Quite a complicated little matter, isn't it?

Actually, for those with a penchant for precision time keeping you will have to set your clocks ahead 1 hour + 1.8 microseconds (millionths of a second). This is to account for a slight speedup in the rotational speed of the earth due to the recent earthquake in Japan, which rearranged the mass of the earth near the equator to make it spin faster. This is like the effect of an ice skater spinning faster as she draws her arms closer to her body during a spin. The Law of Conservation of Angular Momentum says she must spin faster to conserve her angular momentum as her diameter contracts.

For those really really into precision time keeping, you will need to pay attention to the height of the alarm clock in your bed room. According to Einstein's General Theory of Relativity, his theory of gravity, clocks lower or higher than an observer in a gravitational field run slower or faster, respectively, than the observer's watch. In the case of a lower clock, this is called the gravitational red shift. For example, if you have an alarm clock on the floor beside your bed (about 3 feet below where you are sleeping with your wrist watch), it will loose 3.1 picoseconds (1 trillionth, or a millionth of a millionth) per 8 hour night compared to your wrist watch. This could make you late for a very important meeting, if you have to get there exactly on time. You have been warned, so don't be late!


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