This lecture begins our exploration of the
science of astronomy.
We’ll learn about how ancient peoples looked
at the sky, and how their understanding of
the universe evolved into our modern study
of astronomy.
This image was taken on the summer solstice
at Stonehenge in United Kingdom, and it captures
a sunrise involving fog, trees, clouds, and
stones placed about 4,500 years ago, plus
our 5 billion year old star.
Even given the precession of the Earth's rotational
axis over the millennia, the Sun continues
to rise over Stonehenge in a meaningful astronomical
way.
Humans have looked at sky for as long as there
have been humans.
Studying ancient astronomy is a study of the
history of humanity and how our approach to
the natural world has changed.
'Archaeoastronomy' is the study of the astronomical
practices, celestial lore, mythologies, religions
and world-views of all ancient cultures.
Archaeoastronomy is, in essence, as the "anthropology
of astronomy"
Many of our current systems have their roots
in ancient astronomy including timekeeping,
tracking the seasons, calendars, lunar cycles,
watching the planets and stars, and predicting
things like eclipses.
Here's one example of the practical application
of observations: People in ancient Africa
could determine where they were in the rainy
season or dry season just from observations
of the crescent moon.
And here’s an example of what we still live
with today.
The seven days were originally linked to the
Sun and the Moon and the five planets visible
to the naked eye.
These objects were called the “wanderers”
since they appeared to wander among the fixed
stars.
Ancient people could keep track of the time
during the day by watching the Sun’s path
through the sky.
Many cultures probably used sticks and the
shadows they cast as simple sundials.
The ancient Egyptians built huge obelisks
that likely served as simple clocks.
Archaeologists believe Stonehenge was built
between 3000 BC and 2000 BC and that the location
served as a burial ground, and as a social
and religious gathering place.
It also is a means of marking the seasons.
This sketch shows how archaeologists believe
Stonehenge looked upon its completion in about
1550 BC.
Several astronomical alignments are shown
as they would appear from the center.
For example, at summer solstice an observer
standing within the stone circle, looking
north-east through the entrance, would see
the Sun rise above the Heel Stone.
The Templo Mayor was one of the main temples
of the Aztecs.
It featured twin temples on a flat-topped
pyramid.
From the vantage point of a royal observer
watching from the opposite side of the plaza,
the Sun would rise through the notch between
the temples on the equinoxes.
Many cultures aligned their buildings and
streets with north, south, east, and west
directions, which made it easier to keep track
of the changing rise and set positions of
the Sun over the course of the year.
This type of alignment is found from sites
as diverse as the Egyptian pyramids and the
Forbidden City in China, as well as among
ceremonial kivas built by Ancestral Pueblo
People of the American southwest.
This Sun Dagger was created by the Ancestral
Pueblo People in Chaco Canyon, New Mexico.
Three large slabs of rock lie in front of
a carved spiral in such a way that they produced
special patterns of light and shadow at different
times of the year.
For example, at noon on the summer solstice
a single dagger of sunlight would pierce the
center of the spiral.
On the winter solstice, two daggers of light
would bracket the spiral.
Many of the ancient structures have been fairly
straightforward for archaeoastronomers to
interpret, but many other cases are more ambiguous.
For example, ancient people in what is now
Peru etched hundreds of lines and patterns
in the sand of the Nazca desert.
Many of the lines point to places where the
Sun or bright stars rise at particular times
of year, but it could be coincidental.
There are hundreds of lines, so random chance
ensures that many will have astronomical alignments,
no matter how or why they were made.
Many of the patterns are animals, which could
be representative of constellations.
In some cases, archaeoastronomers can use
other clues to establish the intentions of
ancient builders.
For example, traditions of the Inca Empire
of South America held that its rulers were
descendants of the Sun and therefore demanded
close watch of the movements of the Sun and
stars.
This fact supports the idea at astronomical
alignments in Inca cities were deliberate
rather than accidental.
Polynesian navigators used a combination of
astronomy knowledge and an understanding of
the patterns of the waves and swells to travel
great distances among their islands.
Important celestial events were also noted.
This may be one of the earliest known records
of a supernova explosion, or the death of
a supermassive star.
And here is a more modern example of marking
the seasons.
On the solstices, the Sun is located just
right for sunlight to stream through openings
and spell out the term for the longest and
shortest day of the year.
On two other days of the year, watchers of
this sundial might get to see it produce another
word: EQUINOXE.
That’s in for ancient astronomy.
I hope you enjoyed the lecture, and I will
talk to you soon.
