The sky is the most mysterious part of our everyday experience. Familiarity may make the amazing events going on at ground level seem almost ordinary. Plants and animals grow and die. The rain falls and the rivers flow. We feel we understand that. But the sky is beyond comprehension. Two great objects travel through it. One is hot and constant and the other cold and changeable. In the daytime it is moody. There may be blazing sun or racing clouds or darkness followed by thunder and lightning. And yet on a clear night the sky is the very opposite. It is predictable in the night. If you look hard enough with recognizable groups of stars moving in a slow but reliable manner. Interest of the man in the sky is at the heart of three separate stories. These three stories are astronomy and astrology and the calendar. Astronomy is the scientific study of moon and stars. The stars include the sun also. Astrology is a pseudo science interpreting the supposed effect of the heavenly bodies on human existence. In early history the two are closely linked. The sky is the home of many of the gods. These gods influence the life on earth. And the patterns in the sky must surely reflect that influence. Compilers of a calendar attempting to record and to predict the passage of time are offered an easy first step in the cycle of the moon. The only two measures of time available to primitive people are the day and the month. The month is a well adjusted length of time for recalling fairly recent events. A far more important slice of time is the year. It is a full circuit of the earth round the sun. It is crucial in human activities because of its influence on seasons and crops. But the length of a year is exceptionally hard to measure. Primitive societies make do with a broad concept counting the year as starting when leaves sprout on a particular tree or describing someone as having lived through a certain number of harvests. The only simple yet accurate way of measuring a year is in relation to the stars. The stars appear in the night sky at different times and places depending on where the earth is in its orbit round the sun. A star observed in a given place on the horizon at dawn. They will be there again exactly a year later. In Egypt the temple priests derive much of their prestige from close attention to the stars. It enabled them to give the impression of predicting natural events. The best example is their use of Sirius. It is also known as the Dog Star. It rises above the horizon just before dawn at the time of year when the all important flooding of the Nile is about to occur. Priests who can foretell this great event are powerful soothsayers. This observation of Sirius also enables the Egyptians to become the first people to move from a lunar to a solar calendar. In Mesopotamia the Babylonians are the leading astronomers. The calendar is a simple lunar one. So probably is the first Egyptian calendar. The use of lunar based calendar is still prevalent today. The lunar based calendar has a very big disadvantage.