Ancient Calenders and Clocks--Motivation to Study Astronomy!
Celestial
bodies--- the Sun, Moon, planets, and stars--- have provided us a
reference for measuring the passage of time throughout our existence.
Ancient civilizations relied upon the apparent motion of these bodies
through the sky to determine seasons, months, years and the hour of
day. Egyptian Astronomy The earliest Egyptian calendar was based on the moon's cycles, but later the Egyptians realized that the "Dog Star" in Canis Major, Sirius, rose next to the sun every 365 days, about when the annual inundation of the Nile began. Based on this knowledge, they devised a 365 day calendar that seems to have begun in 4236 BC. The Mayans of Central America relied not only on the Sun and Moon, but also the planet Venus, to establish 260 day and 365 day calendars.
We have no
written records of Stonehenge, built over 4000 years ago in England,
but its alignments show its purposes apparently included the
determination of seasonal or celestial events, such as lunar eclipses,
solstices and so on. 
The First Clocks
Egyptians were among the first to formally divide their day into parts something like our hours. Obelisks
(slender, tapering, four-sided monuments) were built as early as 3500
BC. Their moving shadows formed a kind of sundial, enabling people to
partition the day into morning and afternoon. Obelisks also showed the
year's longest and shortest days when the shadow at noon was the
shortest or longest of the year. Later, additional markers around the
base of the monument would indicate further subdivisions of time. 27 Egyptian Obelisks still exist today.
Ancient Shadow Clocks came into use around 1500 B.C. to measure the passage of hours. This device divided a sunlit day into 10 parts plus two twilight hours in the morning and evening. When the long stem with 5 variably spaced marks was oriented east and west in the morning, an elevated crossbar on the east end cast a moving shadow over the marks. At noon, the device was turned around to measure the afternoon hours.
Continued Astronomical Refinements
The merkhet,
the oldest known astronomical tool, was an Egyptian development of
around 600 BC. It uses a string with a weight on the end to accurately
measure a straight vertical line (much like a carpenter uses a plumb
bob today). A pair of merkhets was used to establish a north-south
line (or meridian) by aligning them with the Pole Star. They could then
be used to mark off nighttime hours by determining when certain other
stars crossed the meridian.
Nearly every culture thousands of years ago had astronomers
The importance of keeping track of seasons for planting, flooding or monsoon periods, harvesting,
as well as time keeping, meant astronomy had a central importance in prehistory.