Assessing polynomial approximation for AT

The time based on the rotation of the earth around its own axis is known as Universal Time [UT], it is not a uniform time scale. Another time scale based on the revolution of earth in its orbit around the sun, called Terrestrial time [TT]. The difference between TT and UT is known as delta T [Delta T]. Delta T varies slowly but rather irregularly. The exact value of Delta T cannot be predicted because the rate at which earth's rotation is slowing down is not known. Therefore, delta T can only be deduced form observations. The knowledge of the exact value of Delta T is essential for predicting the correct time of astronomical event or to confirm the time of Historical events. If Delta T is not considered the result may contain an error of several seconds. The value of Delta T can be found in almanacs, where it is given in seconds of times at January 1 for each year but for some calculation of the astronomical events we require its values at any date of the year. In such cases an approximate formula can make the life simple. This paper discuss a polynomial approximation to Delta T for the range of 1620 to 2000 AD published by Jean Meeus and Larry Simons and gives a modified version of this approximation which is much more accurate

comparative study of arithmetic, observational and predicted lunar calendar for Pakistan for years 2000-2004

Arithmetic Lunar Calendar is based on the concept of Leap Years and the average motion of the Moon. However, the actual motion of the Moon varies greatly due to various factors which cause the observational calendar to be different from the arithmetic calendar. Whereas, the Calendars based on prediction criterion of Yallop are the closest to the observational calendar. In this work, we compare these calendars with the actual observational calendar in practice in Pakistan for the years 2000 to 2004. It is found that on average 95% observations are according to the Yallop's criterion. The disagreement is the result of either the bad weather due to which the new Lunar crescent could not be sighted and the Lunar month began one day late, or too optimistic claims of observation and the Lunar month began one day earlier than predicted. On the other hand the disagreement between the Arithmetic Calendar and the observational one is 54%.