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's Ancient Astronomers Part 1 The mediator

I often read on sites frequented by lovers so-called "mysterious archeology" (also known as pseudo-archeology) that ancient peoples could not know certain things without "aid" by the allegations of the more advanced society or ignoring certain information.

For example, you might wonder how the Mayans about the precession of the equinoxes or predict eclipses of the sun or moon without knowing that the Earth revolves around the Sun or the belief that the Earth was flat, and the amazing weather on the motion Venus? How could they do so without the aid of a telescope?

so I got the idea to write some articles that show even with rudimentary means you can get a considerable skills. I will avoid deliberately refer to the sphericity of the Earth, as long as you do not need and - most importantly - the heliocentric theory. This article does not take into account even the night sky.

begin with a solar observatory that allows us to determine the cardinal points and the beginning of the seasons. We will use the technique of Hindu circles.
All we can see some facts:

• the sun rises from the horizon, describes an arc in the sky that leads him to reach a maximum height, which then descends to a setting on the horizon, but in the opposite direction;
• because of this fact in the morning and the evening shadows are longer than at noon;
• less in winter the sun rises and the days are shorter, in particular the length of the days set until around the end of December (until 21) and then increases again;
• in summer the sun rises more and the days are longer, especially since the day length increases towards the end of June (until 21) and then decreased again;
• all ' early spring and fall as hard as the night the day, but with the progress of the season in the spring when day length increases in the fall haul.

We built the observatory. We need:

• a sunny day;
• an open space, possibly broad and flat;
• a long pole and straight;
• a plumb line (or a bubble);
• a long rope;
• stakes (or something that we allows you to draw a sign on the ground);
• time available.

We plant the far post on a flat and straight and clean, where trees and buildings are possibly far away. To help us put it vertically with a plumb line. The sun will cast the shadow of the pole on the ground. We just built a gnomon .

mid-morning marked the point where it comes from the shadow of the gnomon ("A" nella figura) e, usando una corda fissata al palo e un paletto come punta, tracciamo un cerchio intorno al palo che passi per quel punto.



Man mano che la giornata prosegue, l'ombra andrà prima accorciandosi, rimanendo dentro il cerchio, e poi tornerà ad allungarsi. A un certo punto, nel pomeriggio, l'ombra toccherà di nuovo il cerchio. Segniamo questo punto ("B" nella figura).

Segniamo i punti dove l'ombra della punta del palo tocca il bordo del cerchio per identificare la direzione Ovest-Est

Tracciamo la linea che congiunge i due punti. Se ripetiamo il procedimento distance to a week or a month you will notice that the lines we draw, even on different circles, they are all parallel. The line

our two points A and B is the direction west-east. To find the North-South direction, it would suffice to draw the perpendicular to this line through the post. The point is marked in the morning towards West (as the sun rises in the East). That marked the morning indicates the 'East . The pole is the direction South . The North is in the opposite direction. Now we can easily draw a cross with the center pole, indicating the quattro direzioni cardinali.



Se ci accontentiamo di una precisione un po' minore, possiamo usare un foglio di carta su un tavolino messo bene in bolla. Lo gnomone potrebbe essere un chiodo posto verticalmente sul foglio, o una matita. Sul foglio tracciamo subito una serie di circonferenze. Quando - nella mattinata - l'ombra dello gnomone tocca uno di questi cerchi segniamo il punto. Attendiamo l'ombra che tocchi nuovamente la stessa circonferenza ed avremo il secondo punto. Da questo momento in poi valgono le stesse considerazioni del caso precedente.



Se continuiamo a osservare l'ombra del nostro gnomone nei giorni e mesi successivi, noteremo un'altra cosa importante: la sua ombra è più corta quando si stende sulla linea North-South. This happens at the local noon (do not 12:00 am, noon but literally, that is half of the day). At this time the Sun reaches its maximum height in the sky, and then down again.

When crossing this point, the Sun crosses the imaginary circle drawn through the points of the compass North and South, to the highest point of heaven that Zenith - what is exactly above the observer's head and shown by tip of the gnomon - and what exactly lies under her feet, said Nadir . This circle is called the local meridian (word comes from " medius dies", ie " half day).

In the figure, the sun has just reached the highest point on its way: that is culminating ( culmination top or transit) is the meridian passing . This terminology applies to the Sun as well as any other star, both day and night.

During the year we will change the length of shadow in transit. Decrease as we approach the June 21, when it will be the shortest of the year. From that moment on, begin ad aumentare. Il 21 giugno è il solstizio d'estate , il giorno più lungo dell'anno, dove il sole raggiunge la massima altezza.



Dopo il solstizio d'estate l'ombra si allungherà progressivamente. Il 21 settembre capiterà una cosa particolare: il sole sorgerà esattamente ad Est e tramonta esattamente a Ovest: lo possiamo verificare guardando l'ombra del palo che all'alba coprirà il punto che abbiamo indicato come Ovest, e al tramonto quello che abbiamo indicato come Est. In questa giornata il giorno dura esattamente come la notte. Siamo all' equinozio d'autunno .



L'ombra continuerà ad allungarsi (e le giornate ad accorciarsi) until 21 December when it will be the longest of the year. This is the winter solstice, the shortest day of the year during which the sun rises less in the sky.

After this date the days lengthen and return to the shadow to shrink. On March 21 is the ' spring equinox and it will happen that happened on Sept. 21, in the autumn .. The sun will rise exactly east, west and go down exactly what the day will last the night.

The days continue to lengthen until the next summer solstice, and so on.

for this time's it!