How to draw the stars of a Geocentric Universe: (Make your own Heavens' Hinge, Part 4)
This exercise shows how to discover what "the Universe" might have meant for neolithic peoples, particularly in Southern England. It also teaches the concept of rotation of the celestial sphere so may be suitable as a curriculum extra.
The exercise:
In parts 1 and 2, we drew a Geocentric Universe as it might have been seen by neolithic peoples. The drawing we drew was identical to Stonehenge's overall layout of stones. In part 3, we used observation to try to record special features of solar movement about the polar axis. This drawing proved to be identical to Stonehenge's Layout of outer Sarsen stones. In part 4, we'll look at how things might have been seen before the number of the Sun was known. This latest drawing will add an arrangement identical to Stonehenge's Aubrey Holes; constructed in the earliest times.
Location:
You will need to be at the latitude of Southern England for this part to work well. However, if you are not, you can simulate being at 51-52° by finding sloped ground for the first part of the experiment. For example, at Los Angeles, a latitude of 34°, any north facing hill with a slope of 17-18° will simulate being at Stonehenge (51.2°).
Equipment needed:
a) The stone layout generated by our experiment in Part 3
b) Two (min) or seven (max) straight sticks approximately 5 feet long
c) One inexpensive wood clamp (not strictly necessary but useful)
d) 7 large red pegs
e) 7 large blue pegs
f) 14 smaller yellow pegs
g) 28 smaller pink pegs (or uncoloured)
Timing:
a) Any season.
b) Make sure you've done exercise one, two and three first
c) Session can be done at any time; it takes about an hour
The method:
From the earlier experiments, the students will have noticed that the Heavens will revolve around them and they will have drawn the polar axis and the sun's movement. We are going to continue to draw that world exactly as the students would see it, and the students will see themselves as standing at the top of a circle (representing the World).
This was the Part 3 drawing of the Universe in stone:
The North Pole is about 39° anticlockwise from where you are standing. From the Long Man experiment, the students will have checked this. A stick is now laid on the ground and clamped to the pole which points to the North Star. This gives an angle of about 51°:
If you are doing this at a different latitude to Salisbury (as described in Location above) use your hill's slope.
We'll now take our two sticks, lay them on the ground (with east again representing 'up') to locate the equatorial plane (which is at 90° to the polar axis). Then place a couple of red marker pegs near the outer circle:
As the part 3 experiment, rotate the sticks over and locate another peg in the ground:
Now carry on until seven pegs are located. At Salisbury (~51.2°), the latitudes of the heavens divide into seven equal parts (360°/7 equals 51.4°):
We'll now place seven more (light blue) half-way pegs:
Then 14 more yellow half-way pegs:
We have now made an extraordinary discovery: At Salisbury in England, the rotation of the stars can be divided into 28 parts (4 x 7). In our diagram, a yellow marker represents the North Pole axis. A red marker (3 pegs along clockwise) represents the stars rotating directly above us. Another red marker (4 more pegs along) represents the celestial equator. Yet another yellow marker (7 more pegs along) represents the South Pole.
We'll add another 28 pink or plain half-way pegs to complete the drawing of the Heavens:
And this is how it looks as a drawn diagram:
The drawing now has exactly the same number of pegs as there are Aubrey holes at Stonehenge. The Aubrey Holes are one of the earliest features of that monument, built long before any of the stones at Stonehenge were erected:
Post experiment discussion:
The drawing of the Earth is a circle. Stonehenge is arranged as a circle.
At a latitude of 51-52°, Stonehenge's latitude, the celestial sphere can be divided into seven parts.
At a latitude of 51-52°, dividing the celestial sphere into 28 (4 x7) parts, the Poles, the stars directly above and the equatorial axis can be represented.
By dividing into 56 parts (8 x 7), all the stars can be mapped into bands.
Background:
'They [Druids] likewise discuss and impart to the youth many things respecting the stars and their motion, respecting the extent of the world and of our earth, respecting the nature of things, respecting the power and the majesty of the immortal gods.' Commentariide Bello Gallico by Julius Caesar
From the earlier experiment, we saw that the Heavens appear to revolve around us. We have drawn that world exactly as it is seen: The experimenters will have seen themselves as standing at the top of a circle (representing the World).
(If you are looking towards the east, the top of your drawing will be to the east and the bottom will be to the west. If you were to draw yourself, you would be a small dot on the top of the circle. The rest of the universe is described from this 2-D arrangement.)
The North Pole is about 38-39° anticlockwise from where you are standing. This angle is approximately 6/56 (or 3/28) round from the North Pole.
The equatorial line will be 51-52° clockwise from where you are standing. This angle is approximately 8/56 (or 4/28) round from the equator.
Notes:
