CHAPTER 2: THE SCIENCE OF LIFE IN THE UNIVERSE
Astronomy: Next Quiz based on :Go into Chpt 2, Chpt 3.2
2.1 THE ANCIENT DEBATE ABOUT LIFE BEYOND EARTH
Greek efforts marked the first attempts to understand the universe through methods closely resembling the ones we use in science today.
Some scholars argued that there must be life elsewhere, while others, especially Aristotle, argued just the opposite.
Planets are named after Mythological figures because our ancestors looked at the sky and attributed what they saw to the arbitrary actions of mythological beings
How did attempts to understand the sky start us on the road to science?
"The development of science began with Greek attempts to create models to explain observations of the heavens. Although most
Greek philosophers favored a geocentric model, which we now know to be incorrect, their reasons for this choice made sense at the
One of the primary difficulties of the model was that it required a complicated explanation for the apparent retrograde motion of the
planets, with planets going around small circles on larger circles that went around Earth, rather than the much simpler explanation
that we find with a Suncentered model."
At night, the stars circle the sky with different constellations prominent at different times of year.
People of many early cultures believed that Earth is a flat, motionless disk surmounted by a domelike sky across which the heavenly bodies move.
The Sun clearly plays a central role in our lives, governing daylight and dark ness and the progression of the seasons. The Moon’s connection to the tides would have been
obvious to people living near the sea.
These powerful influence is why the sun and the moon had such important role in inside religion during early times, as well as used to keep track of time and season.
Chinese, Babylonians, and Mayans also kept record of astronomical observations.
Thales is this Greek guy who was the first to ask "what is the universe made of" without using supernatural answers. His answer was that Earth was a flat disk on an infinite
This is a shit answer but credit for trying to question. For the first time someone suggested that the world was inherently understandable and not just a result of arbitrary or
Plato and his student Aristotle continued to ask questions. They brought new ideals and it all sucked scientifically because Greeks liked to rely on thought but not observation or experiments.
Then Greeks developed math in the form of geometry, and used it to solve engineering and scientific problems. They also created models of nature, an ideal still central to
A scientific model is a conceptual representation whose purpose is to explain and predict observed phenomena.
Anaximander is this Greek guy that said heavens must form a complete sphere, called the celestial sphere around Earth. He also realized that the Surface of Earth is curved,
but he thought it was a cylinder than a sphere.
Pythagoras is the guy who thought that Earth was a sphere. His reasoning was that he thought Earth should have a geometrical perfection, and a sphere was geometrically
Aristotle looked at the shadow of Earth on the moon during lunar eclipses as evidence for a spherical Earth.
They (Greek philosophers) adopted a geocentric model of the universe, with a spherical Earth at the centre of a great celestial sphere.
Incidentally, this shows the error of the widespread myth that Columbus proved Earth to be round when he sailed to USA.
The early Greek geocentric model consisted of a central Earth
surrounded by the celestial sphere, which is shown here marked
with modern constellation borders and a few reference points and
circles. We still use the idea of the celestial sphere when making
astronomical observations, but we no longer imagine that it
Our sevenday week is directly traceable to the fact that seven “planets”
are visible in the heavens.
While the planets usually move eastward relative to the constellations,
The wanderings of these objects convinced the Greek philosophers that there had to be more
to the heavens than just a single sphere surrounding Earth. sometimes they reverse course and go backward. These periods of
apparent retrograde motion (retrograde means “back ward”) last
The Sun and Moon each move steadily through the constellations, with the Sun from a few weeks to a few months, depending on the planet. completing a
circuit around the celestial sphere once a year and the moon once a month.
A picture from November to June in 29 weeks. This contradicts with Plato's claim that all heavenly objects move in perfect circles. How can something go backwards if it moves in perfect circles?
Ptolemy’s model was the Ptolemaic model. This model
reproduced retrograde motion by having planets move around Earth
on small circles that turned around larger circles. A planet following
this circleoncircle motion traces a loop as seen from Earth, with the
backward portion of the loop mimicking apparent retrograde motion.
It was complicated but it did work, although it put some circles of
centre to get his model to agree with observations.
Aristarchus is this guy that suggested that Earth goes around the sun. He recognized that a Suncentered system offers a much more natural explanation for apparent retrograde motion.
Aristarchus had little success in convincing his contemporaries to accept it. Aristarchus’s idea seemed inconsistent with observations of stellar positions in the sky.
If Earth orbits the Sun, then over the course of each
year we should see nearby stars shift slightly back
and forth relative to more distant stars (stellar
parallax). The Greeks could not detect any such
shift, and used this fact to argue that Earth must be
at the center of the universe. Today, we can detect
stellar parallax with telescopic observations,
proving that Earth does orbit the Sun. (This figure is
greatly exaggerated; the actual shift is far too small
to detect with the naked eye.)
Why did the Greeks argue about the possibility of life beyond Earth?
"Some Greek philosophers (the atomists) held that our world formed among an infinite number of indivisible atoms, and this infinity implied the existence of
other worlds. In contrast, Aristotle and his followers (the Aristotelians) argued that all earth must have fallen to the center of the universe, which rationalized
the belief in a geocentric universe and the belief that the heavens were fundamentally different from Earth. This implied that Earth must be unique, in which case
no other worlds or other life could exist."
Anaximander suggested that all material things arose from and returned to the apeiron, which allowed him to imagine that worlds might be born and die repeatedly through
eternal time. The aperion means "infinite"
He is suggesting that other Earths and other beings might exist at other times.
Generally, Greeks thought world’s having been built from four elements: fire, water, earth, and air. The atomists held that both Earth and the heavens were made from an ininite number of indivisible atoms of each of the 4 elements.
The aristotelians held that 4 elements, not necessarily made from atoms, were confined to the realm of Earth, and while the heavens were made of a distinct fifth element, often
called the aether, or ether, or the quintessence, literally meaning the 5th essence.
The atomists doctrine was developed by Democritus and his views led to belief in extraterrestrial life.
He thinks that both Earth and the heavens had been created by the random motions of infinite atoms.
This idea held that the number of atoms was infinite, it was natural to assume that the same processes that created our world could also have created others.
Aristotle had a different view. He believed that each of the four elements had its own natural motion and place.
For example, he believed that the element earth moved naturally toward the center of the universe, an idea that offered an explanation for the Greek assumption that Earth
resided in a central place. The element fire, he claimed, naturally rose away from the center, which explained why flames jut upward into the sky.
If there were more than one world, there would be more than one natural place for the elements to go, which would be a logical contradiction. Therefore, he doesn't think there
are many worlds.
St. Thomas Aquinas used Aristotle's ideas into Christian theology. The debate about extraterrestrial life became intertwined with debates about religion because the atomist
view of the world coming into existence because of random motions of atoms means there was no need for the Creator (God)
2.2 THE COPERNICAN REVOLUTION
The Library of Alexandria remained the world’s preeminent center of research for some 700 years.
How did the Copernican revolution further the development of science?
"During the Copernican revolution, scientists began to place much greater emphasis on making sure that models successfully reproduced observations, and
learned to trust data even when it contradicted deeply held beliefs. This willingness to let data drive the development of models led Kepler to develop what we now
call Kepler’s laws of planetary motion, and later led to the deeper understanding that came with Newton’s laws of motion and the law of
Copernican revolution: Copernicus revived Aristarchus's suggestion of a Sun centered solar system with enough evidence for it to compete with the Earth cetered model,
Many debates arose and that is how the foundation of modern science first arose.
At Copernicus's birth time, Ptolemaic model was noticeably inaccurate, but few people were willing to undertake such difficult calculations to fix the problem. Copernicus began studying astronomy in his late teens. He soon be came aware of the inaccuracies of the Ptolemaic predictions and began a quest for a better way to predict
Copernicus discovered simple geometric relationships that allowed him to calculate each planet’s orbital period around the Sun and its relative distance from the Sun in terms of
The success of his model in providing a geometric layout for the solar system further convinced him that the Suncentered idea must be correct.
Problem: while Copernicus had been willing to overturn Earth’s central place in the cosmos, he had held fast to the ancient belief that heavenly motion must occur in perfect
In the end, his complete model was no more accurate and no less complex than the Ptolemaic model, and few people were willing to throw out thousands of years of tradition for
a new model that worked just as poorly as the old one.
Danish nobleman Tycho Brahe built large nakedeye observatories that worked much like giant protractors, andover a period of three decades he used them to measure
Tycho never came up with a fully satisfactory explanation for his observations, but someone else did. In 1600, he hired a young German astronomer named Kepler. Kepler was
deeply religious and believed that understanding the geometry of the heavens would bring him closer to God.
But giving up on the idea of perfect circles, he came up with a big finding: Planetary orbits take the shapes of the special types of ovals known as ellipses. This is described in
Kepler's First Law.
A planet’s distance from the Sun varies during its orbit. It
is closest at the point called perihelion and farthest
at the point called aphelion. The average of a
planet’s perihelion and aphelion distances is the length
of its semimajor axis. (The semimajor axis simply
will be referred to as the planet’s average distance from
the Sun.) Kepler’s first law states that the orbit of each planet about the Sun is an ellipse with the Sun at one focus. The ellipse shown here is more “stretched out” than the orbits of
planets in our solar system, most of which are almost (but not quite!) perfect circles.
Kepler's Second Law: As a planet moves around its orbit, it sweeps out equal distance in equal times. This means the planet moves a greater distance when it is near perihelion
that it does in the same amount of time near aphelion, which also means it moves faster when it is nearer the Sun and slower when it is farther from the Sun.
Kepler's Third law: More distant planets orbit the Sun at slower average speed, obeying the precise math relationship of: p2 = a3
Unlike previous models, Kepler's work is not just an abstract idea, but something that reveals a deep, underlying truth about planetary motion.
The success of Kepler’s laws in matching Tycho’s data provided strong