peaclock

Peaclock
or clockwork peacock

...translated text not definitive

This strange mechanical animal is born as a research to realize an universal sundial with conic gnomon, that is a sundial to show italic and babilonic hours at any latitude. When I started to draw it I didn't imagine what I was driving at, it became a peacock only at the end when I looked at the whole and I think to see a peacock. Moreover I reached my scope with an instruments very different from this one but then the 'peaclock' was done and it got an own life.
It became a 'peaclock' because with english language is possibile play on words: it is a peacock and a 'clock' too. This gadget is not so practical, I cannot park it in my garage and it is hard to roam through squares and lands, but I like to think it can be useful for a new entertaining and strolling job, like an ancient trade, I should use a peaclock to tell the time to sunset for any place.
Well, nowadays who are interested to it ?

The italic hours are becoming again in interest, not only for their history but because nowadays it is possible a new reading. We are not in need to know what time is it, there are a lot of watch around us, starting from our wrists, but a sundial may show some different informations not linked to our fast and furious days, rather a sundial may suggests some unusual thoughts about how roll by our day. Now the italic hours are often propose as co-italic, that is with a numbering different from the traditional one so that the number directly indicates hours to sunset. There also is a new way to get these hours with a sundial, it is the conic gnomon and it is the way used by the clockwork peacock.

The conic gnomon

Think to the horizon plane in any place and the Sun orbits with a center in a point on this plane, they are the orbits which appear to a local observer. The picture shows the solstices and equinoctial orbits in a place with 45° latitude.

Now we can consider the Sun at sunset on the three orbits. We consider the center of the Sun and not the upper border of the circle of the Sun, moreover we don't consider the refraction effects which really permit to observe the Sun when it is just below the horizon, for this geometrical construction we consider the sunset as the istant with the center of the Sun on the plane of the horizon.

Each of the three orbits have an intersection point with the hotizon plane, moreover, on each orbit we can set a 15° arc from this point so that we can found the points where lies the Sun an hour before the sunset Because we are first studying the co-italic hours we consider the half-plane bounded by the meridian line, we chose the half-plane which intersects the three orbits in their sunset points; I may consider the other half-plane to study the babilonic hours.

Now we can better study this geometrical model if we turn it so that the polar axes becomes vertical. Looking at the picture we can know that revolving the half-plane around the polar axes it reaches a new position where it intersects the orbits in the points where the Sun is an hour before the sunset. There is a simply demonstration, because every point of the half-plane turn of the same arc, a point of the plane on the orbit keeps it position on the orbit and move itself of that arc.

We have drawen the half-plane of the horizon which is equivalent to the italic hour 24, now we may draw another plane revolving the first one by 15° and equivalent to the italic hour 23. Going on to revolve of 15° and drawing these half-planes we get all the 24 italic half-planes, each of them equivalent to an italic hour.

The italic half-plane is the half-plane where lies the Sun because the italic hour is the number of the plane no regarding to the declination of the Sun. These half-planes intersect the polar axes in the center of the orbit so this center may be casted on the lines intersection between the half-planes and any orientation dial.

Looking at the whole half-planes we may observe they envelop a cone which axis is the polar one, moreover the polar axis has an altitude above the horizon equal to the latitude so that the cone has a vertex angle twice the latitude. We would get the same cone starting from the babilonic half-planes.

This means we may realize a cone with a polar axis, tangent to the horizon because with a vertex angle twice the latitude and with the tangent planes corrisponding to the italic and babilonic planes. This cone casts its shadow on the horizon showing italic and babilonic time, or both of them, on the hour lines intersection between the horizon and the tangent planes.

The conic gnomon has a angle of 0° at the equator, it is a line, and it has an angle of 180° at the pole where it is a plane. The last picture shows the variation of the cone for latitude from 10° to 80° with step of 10°.

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