An ephemeris is a data based on the positions of the celestial objects in the sky during a particular time period. In the olden days, tables were made with calculated values based on the positions of the astronomical objects or satellites in the sky. Nowadays, modern ephemerides are computer generated electronically from the mathematical charts of the movements of the astronomical objects. Sometimes, hand-printed ephemerides are still generated when computer data is not available. Modern ephemeris can be generated by software that calculates the present positions of the planets and their satellites at any time required by the user. Ephemerides calculate on the basis of the data of several centuries of the past and future. The future data can be generated because of the advancement in the field of celestial mechanics which has given many accurate theories. Though most of the data calculated is accurate, some still cannot be accurately generated because the position of the planets can be perturbed by asteroids. Asteroids have a very uncertain orbit and mass. New data and observations keep coming up and this causes the NASA’s Jet Propulsion Lab to revise its earlier published ephemerides every year. This has been happening since the last 20 years. Ephemerides are also extremely important for the navigation of future spacecraft and any other space activity for the scientists. It can be used to calculate the exact location of a comet after its discovery. Ephemerides calculate the positions of the celestial objects in their right declination and ascension because these same coordinates are also used on telescopes and star maps. Only what is required is the actual equinox or standard equinoxes. Ephemerides also help to ascertain useful information about the planets, asteroids and others beyond pure co-ordinates such as distance, velocity, brightness, time of rise, transit, etc. Ephemerides of Saturn also help to ascertain the inclination of its ring. Ephemeris data provides a precise location to the one GPS requester. The lifespan of an ephemeris data is 30 minutes after which all the GPS requests require another recollection data. An almanac data is useful when this GPS receiver is switched on after 30 minutes. This establishes the location of the GPS receiver. In this way, both Ephemeris and Almanac are used together to determine the required location. Ephemeris data deciphers the path of the satellite on which it orbits the Earth. A Modern Nautical Almanac or Air Almanac also helps to ascertain the position of the celestial objects when an ephemeris is not available. Ephemeris read the accurate information only for certain locations on Earth. But for the moon or some nearby asteroids, they are very helpful for space study. Ephemeris of the moon and planets (EPM) is the modern ephemeris created by the Russian Institute of Applied Astronomy and the INOP is a creation of the French IMCCE. Photographer’s Ephemeris is a free software for those photographers who need to study the times of the twilight and the setting and rising times of the sun and moon.