This document provides a history of astronomy from ancient Greece to modern times. It describes how early Greek astronomers like Aristotle and Hipparchus made early observations of celestial objects but believed in a geocentric model where Earth is the center. Ptolemy later created an elaborate geocentric model, though Copernicus, Kepler, and Galileo provided evidence supporting a heliocentric model through observations, Kepler's laws of planetary motion, and Galileo's discoveries with the telescope. Newton later unified physics and astronomy by formulating the law of universal gravitation. Einstein then revolutionized our understanding of motion, space, and time through his theory of relativity.
2. Early Astronomy
Astronomy is the science
studying outer space and the
universe.
The
“Golden Age” of astronomy
was centered in Greece.
3. Early Astronomy
The Greeks took measurements
of distant objects such as the
Sun and the moon.
Famous Greek
philosopher, Aristotle, conclude
d Earth is round because it
always cast a curved shadow on
the moon.
Another Greek
astronomer, Hipparchus, deter
mined the location of almost
Aristotle (384-322 B.C.)
Hipparchus (190-120
B.C.)
4. Geocentric Model
The Greeks believed in a geocentric
universe, in which the known planets
and the Sun revolved around the Earth.
The path of an object as it goes around
another object in space is called an orbit.
Beyond the planets was an invisible
sphere on which the stars traveled daily
around Earth celestial sphere
The Greeks attempted to explain the
movements of all celestial bodies in space
by using this geocentric model.
5. Ptolemaic System
The Greek
astronomer, Ptolemy, presented a
geocentric model of the universe
called the Ptolemaic System, with
fixed stars in the background.
Although Ptolemy’s
theory was
wrong in that the planets do not
orbit Earth, it was able to account
for the planets’ apparent
motions, which he called epicycles.
Ptolemy (90-168 A.D.)
6. Geocentric Universe
The idea that the earth is at
the center of the universe and
all things fall around her is the
simplest and longest lasting
universal view that we have
had.
7. What the Geocentric Universe is made
of
Sun
Moon
Stars
5 Planets
Mercury
Venus
Mars
Jupiter
Saturn
How
did they
discover the
existence of
these planets?
8. Assumptions about the
Universe
1. The earth is the center of all
motion.
2. The earth does not move.
3. The earth is flat.
4. Planets move in circular orbit.
5. Stars are immutable.
9. Heliocentric Model
The first Greek astronomer to
propose a heliocentric universe, in
which Earth and the other planets
orbit the Sun, was Aristarchus.
Though much evidence was
provided to support a heliocentric
universe, the Earth-centered
(geocentric) view dominated
Western thought for 2000 years.
Aristarchus (312-230
B.C.)
10. The Birth of Modern Astronomy
After Ptolemy, very few advances
were made in astronomy.
The first great astronomer to
emerge after the Middle Ages was
a man from Poland named
Nicolaus Copernicus.
He believed the Earth was a
planet, just like the other 5 known
at the time, and supported the
heliocentric model of the universe.
Copernicus (1473-1543)
Father of Modern
Astronomy
11. The Birth of Modern Astronomy
After the death of Copernicus came a
Danish astronomer, Tycho Brahe.
Brahe became interested in astronomy
from viewing the astonishing effects of a
solar eclipse.
Had an observatory built where he
designed instruments in order to view and
measure locations of celestial bodies.
Still believed in a geocentric universe based
on his observations of stars.
Gained recognition for being extremely
precise on his observations.
Brahe (1546-1601)
12. Summary of Brahe's
Contributions
He made the most precise observations
that had yet been made by devising the
best instruments available before the
invention of the telescope.
His observations of planetary
motion, particularly that of
Mars, provided the crucial data for later
astronomers like Kepler to construct our
present model of the solar system.
13. The Birth of Modern Astronomy
Before Brahe died he hired an
assistant, Johannes Kepler, who
carried on and inherited all of Brahe’s
works.
Didn’t agree Brahe’s view of a
geocentric universe.
Discovered 3 Laws of Planetary
Motion:
1. The path each planet takes around the
Sun is oval-shaped and known as an
ellipse.
Kepler (1571-1630)
14. The Birth of Modern Astronomy
2. Each planet revolves so an imaginary line connecting
it to the Sun sweeps over equal area in equal time
intervals. A planet travels faster when it is closer to
the Sun and slower when it is farther from the Sun.
15.
16. The Birth of Modern Astronomy
3. The square of a planet’s orbital period (the time it
takes to orbit the Sun) is proportional to the cube of
its average distance to the Sun:
The orbital period of revolution (P) is
measured in Earth years. The planet’s
distance (a) to the sun is expressed in
astronomical units (AU’s), which is
the average distance between the
Earth and the Sun, approximately 150
million km. or 93 million miles.
17. The Birth of Modern Astronomy
Galileo Galilei was a great Italian
scientist during the Renaissance.
His most important contributions were
his descriptions of the behavior of
moving objects.
Everything prior to Galileo was studied
and examined without a telescope.
He constructed his own telescope and
used it to study the sky, making many
important discoveries supporting
Copernicus’s view of the universe.
Galileo (1564-1642)
18. Galileo: the Telescope &
the Laws of Dynamics
Galileo Galilei (1564-1642)
was a pivotal figure in the
development of modern
astronomy, both because of
his contributions directly to
astronomy, and because of
his work in physics and its
relation to astronomy.
He provided the crucial
observations that proved the
Copernican hypothesis, and
also laid the foundations for a
correct understanding of how
objects moved on the surface
of the earth (dynamics) and
of gravity.
19.
20. The Telescope
Galileo did not invent
the telescope (Dutch
spectacle makers
receive that credit –
Hans Leppershey), but
he was the first to use
the telescope to study
the heavens
systematically.
It is said that what
Galileo saw was so
disturbing for some
officials of the
Church that they
refused to even look
through his
telescope; they
reasoned that the
Devil was capable of
making anything
appear in the
telescope, so it was
best not to look
through it.
21. Sir Isaac Newton and the
Unification of Physics & Astronomy
Sir Isaac Newton
(1642-1727) was by
many standards the
most important figure
in the development of
modern science. Many
would credit him and
Einstein with being the
most original thinkers
in science
22. Sir Isaac Newton: The
Universal Law of Gravitation
There is a popular story
that Newton was sitting
under an apple tree, an
apple fell on his
head, and he suddenly
thought of the Universal
Law of Gravitation. As in
all such legends, this is
almost certainly not true
in its details, but the story
contains elements of
what actually happened.
23. Albert Einstein and
the Theory of Relativity
Motion is relative not absolute.
Other striking consequences are
associated with the dependence of space
and time on velocity: at speeds near that
of light, space itself becomes contracted
in the direction of motion and the
passage of time slows. Although these
seem bizarre ideas (because our
everyday experience typically does not
include speeds near that of light), many
experiments indicate that the Special
Theory of Relativity is correct and our
"common sense" (and Newton's laws)
are incorrect near the speed of light.
24. SUMMARY
Galilean satellites
Earth is the
center of motion
Galileo
Phases of Venus
Earth IS flat
Newton
Earth is does not
move
Einstein
Planets move in
circular orbits
Kepler
Stars are
immutable
Brahe
Universal Law of
Laws of Motion
Gravitation
Theory of Relativity
Laws of Planetary
Motion
Supernova
