Astronomy in Ancient Civilization. In order to understand the future, we must look to the past. Astronomy impacted ancient civilizations. The major driving force in ancient astronomy studies was SURVIVAL. When will rainy/dry season come? When should crops be planted/ harvested? Navigation.
Astronomy in Ancient Civilization
In order to understand the future, we must look to the past
The major driving force in ancient astronomy studies was SURVIVAL.
When will rainy/dry season come? When should crops be planted/ harvested?
Huge temples and pyramids were built to have a certain astronomical orientation.
The constellation Orion represented Osiris, who was the god of death, rebirth, and the afterlife.
The Milky Way represented the sky goddess Nut giving birth to the sun god Ra.
The center of Egyptian civilization was the Nile River, which flooded every year at the same time and provided rich soil for agriculture.
The Egyptian astronomers, who were actually priests, recognized that the flooding always occurred at the summer solstice, which was also when the bright star Sirius rose before the Sun.
The priests were therefore able to predict the annual flooding, which made them quite powerful.
The Maya were extraordinarily good astronomers, making observations and recording the motion of the Sun, the Moon, and the stars.
*Venus was very important to them
Prior to 36 B.C., this civilization in southern Mexico and northern Central America had begun to use a 360-day year to produce a very accurate calendar and measuring long intervals of time.
The ancient Maya are also known for having had the only known fully developed written language of pre-Columbian America, and the most advanced mathematics and astronomy.
The Aztec Sun Calendar is a large round stone, 12 feet across weighing in at 24 tons.
The calendar was three feet thick as well, so it was not small by any means.
The Sun Calendar took more than 50 years to make, which is quite impressive considering the fact that the Aztecs did not have a hammer and a drill to use.
The twenty calendar days in the month are represented by twenty things in nature and in everyday life that the Aztec people were familiar with.
According to ancient Aztec astronomy, there were 365 days of the year but only 360 were accounted for, as five of them were days for sacrifice.
STONEHENGE is perhaps one of the best known sites of ancient astronomical pursuits.
It is located in Salisbury Plain, England
It is an ancient stone circle from the stone age
Researchers believe it was a calendar or almanac
Its construction began around 2800 bc and continued until 1100 bc
The Big Horn Medicine Wheel in Wyoming is similar to Stonehenge in design
It was built by the Plains Indians
Its spokes align roughly with solstices and equinoxes
Contribution of Scientists
It is to them we owe our thanks.
Around 140 ad, a Greek astronomer named Claudius Ptolemaeus (known today as Ptolemy) constructed perhaps the best geocentric model of all time.
Geocentric = Earth-centered universe
It explained remarkably well the observed paths of the five planets then known, as well as the paths of the Sun and the Moon.
However, to achieve its explanatory and predictive power, the full Ptolemaic model required a series of no fewer than 80 circles.
The Ptolemaic picture of the universe survived for almost 13 centuries until a sixteenth-century Polish cleric, Nicholas Copernicus rediscovered Aristarchus’s heliocentric (Sun-centered) model.
Copernicus asserted that Earth spins on its axis and, like all other planets, orbits the Sun. Not only does this model explain the observed daily and seasonal changes in the heavens but it also naturally accounts for planetary retrograde (backward) motion and brightness variations.
The critical realization that Earth is not at the center of the universe is now known as the Copernican revolution.
Copernicus’s ideas were never widely accepted during his lifetime. By relegating Earth to a non-central place within the solar system, heliocentricity contradicted religious doctrine of the Roman Catholic Church.
His book On the Revolution of the Celestial Spheres was not published until 1543, the year he died. Only much later did the Copernican theory gain widespread recognition.
Having heard of the telescope invention (but without having seen one), Galileo built a telescope for himself in 1609 and aimed it at the sky. What he saw provided much new data to support the ideas of Copernicus.
He revolutionized the way science was done, so much so that he is now widely regarded as the father of experimental science.
The Moon has mountains, valleys, and craters—terrain in many ways reminiscent of that on Earth.
The Sun has imperfections—dark blemishes now known as sunspots. By noting the changing appearance of these sunspots from day to day, Galileo inferred that the Sun rotates, approximately once per month.
Four small points of light, invisible to the naked eye, orbit the planet Jupiter. He realized that they were moons, circling that planet just as our Moon orbits Earth. Clearly, Earth was not the center of all things.
Venus shows a complete cycle of phases, This finding can be explained only by the planet’s motion around the Sun.
In 1610 Galileo published his findings and conclusions supporting the Copernican theory, challenging both scientific orthodoxy and the religious dogma of the day.
In 1616 his ideas were judged heretical. Both his works and those of Copernicus were banned by the Church, and Galileo was instructed to abandon his astronomical pursuits. This he refused to do and instead continued to amass and publish data supporting the heliocentric view. These actions brought Galileo into direct conflict with the Church.
The Inquisition forced him, under threat of torture, to retract his claim that Earth orbits the Sun, and he was placed under house arrest in 1633. He remained imprisoned for the rest of his life.
Not until 1992 did the Church publicly forgive Galileo’s “crimes.”
At about the time Galileo was becoming famous for his telescopic observations, Johannes Kepler, a German mathematician and astronomer, announced his discovery of a set of simple empirical (based on observation) laws that accurately described the motions of the planets.
While Galileo was the first “modern” observer, who used telescopic observations of the skies to confront and refine his theories, Kepler was a pure theorist. He based his work almost entirely on the observations of another scientist (in part because of his own poor eyesight).
Kepler’s First Lawhas to do with the shapes of the planetary orbits:
The orbital paths of the planets are elliptical (not necessarily circular).
An ellipse is simply a flattened circle.
The eccentricity of an ellipse is basically its flatness (Larger # = more oblong)
A perfect circle’s eccentricity is zero.
Two of the most important points of orbit are the planet’s perihelion (its point of closest approach to the Sun) and its aphelion (greatest distance from the Sun).
Orbit time A=B=C
Kepler’s Second Lawaddresses the speed at which a planet traverses different parts of its orbit:
An imaginary line connecting the Sun to any planet sweeps out equal areas of the ellipse in equal intervals of time.
While orbiting the Sun, a planet traces the arcs (labeled A, B, and C) in equal times. When a planet is close to the Sun, it moves much faster than when farther away
These laws are not restricted to planets. They apply to any orbiting object.
Kepler based his work almost entirely on the observations of Brahe.
Those observations, which predated the telescope by several decades, had been made by Kepler’s employer, Tycho Brahe, arguably one of the greatest observational astronomers who ever lived.
Tycho’s observations made with the naked eye were of very high quality.
He had one of the most brilliant minds the world has ever known.
Legend has it that seeing an apple fall gave Newton the idea that the same force that keeps us bound to the Earth also controls the motion of planets and stars.
Newton's contributions to science include the universal law of gravitation and the development of calculus.
He is also famous for his book, Principia Mathematica, in which he presents three laws of motion….
Three Laws of Motion:
Newton’s First Law:
An object at rest remains at rest and a moving object continues to move forever in a straight line with constant speed until a force acts on it.
Newton’s Second Law:
The acceleration of an object is directly proportional to the net applied force and inversely proportional to the object’s mass.
Formula: a = F/m
Newton’s Third law:
Forces always occur in pairs—if body A exerts a force on body B, then body B exerts an equal force on body A, but oppositely directed. (For every force there is an equal and opposite force)
In 1905, Einstein presented his Special theory of Relativity, which made bold statements about the nature of light and the equivalency of matter and energy.
Later, in 1916, he presented General Relativity, on the link between gravity and space and time, which were verified three years later. Einstein also studied the properties of elementary particles and warned of the dangers of nuclear war.
"I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones."
Hubble's extensive observations of galaxies helped him develop the idea of an expanding universe, which forms the basis of modern cosmology.
He also identified a relationship between a galaxy's speed and its distance, the ratio of which is called Hubble’s Constant. A project of the Hubble telescope, currently exploring outer space, is to accurately measure this constant.
The Hubble Constant is the speed at which the universe is expanding.
Women in Astronomy
Maria Mitchell was the first female professor of astronomy in the United States. She discovered the Comet of 1847.
After Mitchell's death, a crater on the moon was named after her.
Henrietta Swan Leavittis known for her 1904 discovery of a type of variable stars named cepheid variables. Cepheid variables are stars that go through cycles of brightness and darkness. Henrietta found that when observing a cepheid variable in another galaxy, she could relate the length of the brightness cycle to the size of the star.
With this discovery, she was able to determine the distances between stars and the Earth. Cepheid variables are referred to as "astronomical yardsticks" as they make it easier to measure distances within the universe.