I'd not heard of Wurdi Youang before reading a newspaper article about it the other day.
Observations of the sun?
Wurdi Youang is near Little River, between Melbourne and Geelong. It's on open grassland which is on the western Victorian basalt plain, meaning there are loads of rocks strewn all over the place from the "relatively" recent volcanic eruptions of places like Tower Hill. You will have seen the sort of place we're talking if you've driven along the Hamilton Highway towards Warrnambool. Seriously, lots of rocks.
Based on nearby artifacts, the site is likely to be over 10,000 years old. If it really were a solar observatory, and it certainly has that appearance, that would make it the world's oldest. Just think of that.
Wurdi Youang is a sort of egg-shaped oval of boulders, some of them very large. The long axis of the oval is oriented east-west, and its makers appear to have made their observations from the easternmost point.
|Photo by Ray Norris via Wikipedia|
From this point, the three largest stones on the far side mark the position of surrounding hills (you can see this in the photo above). Outlying stones mark the position of the setting sun at the Autumn and Spring equinoxes. What's more, the straight lines of stones that radiate from the observation point to the position of the setting sun at the Summer and Winter solstices.
I'm amazed at the sophistication and accuracy of all this.
Clearly, knowing accurately what time of year it is, as well as what time of year is around the corner would be of great benefit to local communities. Knowing where to be at the right time of year and when to plant crops might make the difference between life and death. Agricultural communities as well as nomadic communities would benefit from this.
How would you do this?
For the astronomers to have been constructed this would have required a lot of things.
First, they would have had to notice that the sunsets move north and south of a centre point over the course of the year, and that this movement repeats each year. This requires observations from the same location over a period of years.
You can see in the photo below where the sun sets at the solstices and the equinoxes. (Remember that Australia is in the Southern Hemisphere and so the sun sinks towards the left as it sets.)
|Photo: Ray Norris (graphic by John Morieson) via UNESCO Astronomy and World Heritage Webportal|
Next, the society would have to decide to record where the sun sets each night. This would have needed a method (what type of observatory was appropriate), as well as a lot of planning. This is more than a single individual would easily do.
After deciding what point the observations had to be made from, someone would have to stand there at sunset and direct others to move rocks to a spot far enough away to make the observation accurate, but not so far as to make the construction impractical. This would gradually create the western arc.
Eventually, at some stage in the first six months of detailed observations, the astronomer would be able to record that the sun's position at sunset had stopped moving to the north or south, and had started moving back again.
Knowing the Victorian weather in winter, I would expect the winter solstice would have taken years to pinpoint. The summer solstice would have been easier, with fewer clouds.
Astronomers have been irritated by clouds for millennia!
When constructed, the western arc would indicate what time of year it was. To determine what time of year it is, the observer would stand at the easternmost point at sunset and see where the sun was in relation to the arc rocks to the west. An accurate knowledge of what time of year it was and what was coming would prove a huge benefit to the society.