Shifting zodiacal signs made the news recently. Asking what a lady’s sign is has become an indeterminate question. You should also realize that time zones shift for the same reason! The rotation of the Earth is not synchronized with its orbit around the Sun or anything else. It is also changing. A day was 86,400 mean solar seconds in 1900. It is now more than 86,400 atomic seconds.
There are about a dozen time zone changes in the world each year! There is a strong political element, since which stock bid gets to Wall Street first is important. Most big companies maintain presence in Hawaii so that contracts with a midnight deadline have 5-9 additional hours depending on where the customer is in the U.S. The stock market does this down to less than the millisecond level.
The meridian used to reference civil time and time zones are gradually moving out of Greenwich. Time zones are shifted perceptibly at regular intervals. The Olson Timezone Database helps you figure out what time it really was when something happened in the past somewhere. Unfortunately it is accurate only since about 1970. Think about it. But don’t take too long because you might find yourself an hour later than you thought.
, where you will learn that these phenomena are supported in UNIX, LINUX and Java but not in .NET. Why? Because Poul-Henning Kamp, arguably one of the fathers of UNIX, knows about time. Be careful if you are an astrodynamicist or astronomer.