The Role of Astronomy
In this module we are concerned with how astronomy dealt with the problem of defining a specific time in the year, a reference point in the cycle of the seasons.
The Sun
One way to “measure” the time of year is to observe the height (altitude) of the Sun in the sky. A simple way is to put a stick in the ground and to watch its shadow. When at about midday the shadow is the shortest within one year of observations, it will be around midsummer, when the shadow is the longest, then you know it is around the middle of winter. The position of the shadow also tells you the time of day. Essentially this is a sundial and they go back as far as 1500 BCE. More...
The Stars
With the stars there are other ways of judging the time of year. The visible stars change position slightly from night to night and they move around the sky throughout the year. Different constellations are visible at different times of the year. This also depends on where you are on Earth and each local civilisation used there “own” stars and constellations. But for several reasons, both practical and spiritual, there was a need to be more precise in knowing the time in the year.
It is striking that many civilisations throughout the world have applied the same technique, utilising what is called the heliacal rising of celestial bodies, to define a specific time of the year with a precision of a few days.
This technique observes when a certain star or constellation is visible for the first time in the year, just before sunrise. Which stars to use depends on the location on Earth, and sometimes people were interested in different parts of the season, but the basic technique has been the same.
The New Zealand Māori have traditionally used this method to define the start of the New Year.
They observed the heliacal rising of Matariki, the open cluster generally called Pleiades.