Intihuatana

The Indians, the Egyptians, the Greek and the Mayans observed and clearly understood the movement of the Sun, the moon, the planets and the stars. The Incas did the same and the Machu Picchu ruins clearly demonstrate the Incas' mastery of astronomy!

1) Intihuatana

In "Quechua", the language of the Incas, "Inti" means the "Sun" and "huata" means "to tie". Intihuatana means the "To tie the Sun" or "The hitching post of the Sun". Incas were Sun worshipers and had a very precise understanding of the northern and the southern movement (solstices) of the Sun. Situated at the top of a hill, at the highest elevation at Machu Picchu, is a granite structure called Inithuatana. 

During the Southern Hemisphere's winter solstice, June 21st (summer solstice for the Northern Hemisphere), the Sun is farthest at north. After the winter solstice, the Sun starts moving south. The Incas built the Intihuatana to accurately predict the Winter solstice day. The Inithuatana is considered as the most important part of Machu Picchu.
 

The Intihuatana is at the top of the hill (middle, top of this photo).

The Intihuatana is sculpted on granite rock at the top of the hill.
The Incas used the shadow cast by the pillar to accurately predict their winter solstice.

On the Winter solstice morning, the rising Sun casts the shadow of the pillar to fall on curved notch, carved
on to a flat rock near the Intihuatana. When the shadow falls on the curved notch,
Incas knew that the Sun is going to start turning back towards South.
The flat rock with the curved notch on it is at the center, at the edge of the hill.

Close up view of curved notch.

2) Sun Temple

The second most important building in the ancient city of Machu Picchu is the Sun Temple. Wherever you see a curved/elliptical wall built by the Incas in Peru, you can safely assume it is to do with the Sun. I wonder if that is do with the Incas' knowledge of earth's elliptical path around the Sun.

The Sun Temple with a curved wall and the two windows to
keep track of the summer and winter solstices.

The Sun Temple.

There is no access to the inside of the Sun temple. Either you can see it from below or from the top. Only the walls were built buy the Incas and the rock inside is natural rock on the hill and is considered sacred by the Incas. During the Incas' summer (December) solstice, when the Sun's rays rise over a natural V-shaped notch on the top a mountain, 2 miles away, it enters through one of the windows and shines on the rock inside the Sun temple. During the Incas' winter (June) solstice, the same phenomenon happens through another window precisely placed on the curved wall. I have tried to show the path of the Sun light through these two windows during the summer and winter solstices with red lines in the next photo.

The two trapezoidal windows on the curved wall of the Sun temple are perfectly aligned to keep track of the June and December solstices.

It is really mind-boggling to think how the Inca engineers aligned the Solstice Sun, the V-notch in the mountain and the windows of the Sun temple. With no calendar system to keep track, this is only possible after years and years of observing the sky.

3) Rock shaped like Southern Cross

The constellation  known to us now as "Southern Cross", visible only from southern latitudes, is of great importance to the Incas. When the Southern Cross rises over the Incas' sacred mountain, Salkantay in May, it is the arrival of the rainy season for the Incas. 

In Machu Picchu, near the Initihuatana area, one of the rocks is sculpted exactly like the Southern Cross. Researchers have confirmed that this rock points to exactly the top star of the Southern Cross.

Rock sculpted like the constellation Southern Cross

Highlighted (or dark-lighted) the Southern Cross constellation in this photo I took in Peru. 

These three structures in Machu Picchu are definitely dedicated to astronomical events of great importance to the Incas.  They were very precisely and strategically placed in order to accurately predict change of seasons to help with their agricultural activities.