Whats the difference between “ephemeris time” and “greenwich mean time”?
The moment we think of measurement of time, most of us recollect either grandfather’s clock or our first Physics pendulum experiment using string and mass during school days. We also know how to adjust the period of this pendulum by increasing or decreasing its length. Yet another factor control this period is the earth’s gravity while mass of the pendulum has no effect. This mechanical clock when synchronized with the mean solar time, it gives us the time on 24-hour basis. The mean solar time can be defined as a mean Sun which moves eastward along the celestial equator at average rate of true Sun. Greenwich Mean time(GMT) or Universal Time(UT) is simply a mean solar time measured from Greenwich, England and used in navigation and surveying for hundreds of years. Each country adopts its standard time based on standard meridian with respect to Greenwich. Though look simple, what if earth does not spin in its axis at uniform and constant rate? Well, there is a problem, Earth loses about
