Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0 longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle (ERA, which serves as a modern replacement for Greenwich Mean Sidereal Time). UT1 is the same everywhere on Earth. UT1 is required to follow the relationship

ERA = 2(0.7790572732640 + 1.00273781191135448Tu) radianswhere Tu = (Julian UT1 date - 2451545.0).

Sir Sandford Fleming (January 7, 1827 – July 22, 1915) was a Scottish Canadian engineer and inventor. Born and raised in Scotland, he emigrated to colonial Canada at the age of 18. He promoted worldwide standard time zones, a prime meridian, and use of the 24-hour clock as key elements to communicating the accurate time, all of which influenced the creation of Coordinated Universal Time. He designed Canada's first postage stamp, produced a great deal of work in the fields of land surveying and map making, engineered much of the Intercolonial Railway and the first several hundred kilometers of the Canadian Pacific Railway, and was a founding member of the Royal Society of Canada and founder of the Canadian Institute (a science organization in Toronto).