Modern Astronomy
Unit 1
Ms. Hargrove
AstronomyThe Original Science
Imagine that it is 5,000 years ago. Clocks and modern
calendars have not been invented. How would you tell
time or know what day it is?
One way to tell the time is to study the movement of
stars, planets and the moon. Studying the ancient skies
was so important that ancient people built labs for them
to observe their studies.
Over time, the study of the night sky became the science
of Astronomy. Today Astronomy is known as the study of
the universe.
Who’s Who of Early Astronomy
• The careful work of early astronomers
helped people understand their place in
the universe.
• Almost everything early astronomers
knew about the universe came from
what they could discover with their eyes
and minds.
• https://www.youtube.com/watch?v=Ge
vV1yvMJbc
Geocentric or Heliocentric?
•Of the early philosophers, only a few
favored the heliocentric model
•Most philosophers thought that their
studies supported the Geocentric model
more than the Heliocentric model
Geocentric Evidence
“Earth-Centered Universe”
• Everything appears to revolve around the Earth each day.
• There is no observable features present of the stars, planets, Moon,
or Sun in this model.
Problems With the Geocentric Model
• The planets appear to change brightness, implying a
change of distance.
• The planets undergo retrograde motion “Spiral Motion”
• They move backwards compared to the direction the Sun moves.
• Why would perfectly circular motion reverse itself?
• The Sun, Moon, and Planets do not move at the same
speed all the time.
• Didn’t explain why Mercury and Venus stayed close to the
Sun
• https://www.youtube.com/watch?v=46WHSTNZTfg
Evidence of the Heliocentric Model
• The changing brightness of the planets is explained by
the Earth getting closer and farther from the planets
during our orbit of the Sun.
• Mercury and Venus no longer “block” the Sun from
the Earth because they orbit the sun, just as we on
Earth do.
Heliocentric
“Sun-Centered Universe”
Problems with the Heliocentric Model
• The changing speeds of the Sun, Moon, and planets
is not explained by simply placing the Sun at the
center of the universe.
• We do not feel the Earth moving
• If the Earth were spinning, wouldn’t we be thrown
off into space?
So Which One Did They
Favor?
• The ancients favored the geocentric model because it seemed
impossible to believe that the Earth was moving.
Who Were These Astronomers???
Aristotle
Earth-Centered Universe
• 384 BC to 322 BC
• Made contributions to all areas of philosophy but math was his
weakness
• He did not believe that “solid proven” evidence was necessary to
prove ideas.
• Aristotle is one the first to attempt to create a scientific model of the
universe.
• This model has now become known as the “Geocentric Model” which
places the “imperfect” Earth at the center and all of the “perfect”
objects (Sun, Moon, Planets, etc.) go around us in a circular motion
Ptolemy
Earth-Centered Universe
• About 85 AD to 165 AD
• About 85 AD to 165 AD Ptolemy is the most influential
astronomer in his day and his models of the universe
will prevail for the next 1400 years
• Ptolemy is a great theorist of the geocentric model.
• Ptolemy is also accused of stealing ideas without
crediting his source.
• He saw that there were problems with Aristotle’s
simplistic idea of a geocentric model.
• Ptolemy employed an old idea of epicycles to help
explain the discrepancies in the evidence for Geocentric
Model.
Ptolemy:
An Earth-Centered Universe
• Ptolemy wrote a book that combined all of the ancient
knowledge of astronomy that he could find. He then expanded
on it with careful mathematical calculations.
• Ptolemy thought that the Earth was at the center of the universe
and that the other planets and the sun revolved around the
Earth.
• Perfected the Geocentric Theory
Copernicus
Sun-Centered Universe
• A Polish astronomer from 1473 to 1543
• Revolutionized astronomy with his new theory
• Heliocentric theory-the sun is at the center of the universe, and all of
the planets, including the Earth, orbit the sun.
• The theory correctly explained the movement of the planets around
the sun but it did not replace Ptolemy’s theory immediately.
Nicolas Copernicus
He wrote a book in
1514 outlining his
basic arguments for
the Heliocentric
universe.
He only allowed
friends to read it and
did not put his name
on it.
Copernicus’ Theory
1.
2.
3.
4.
There is no one center in the universe.
The Earth’s center is not the center of the universe.
The center of the universe is near the Sun.
The distance from the Earth to the Sun is impossible to be
compared with the distance to the stars.
5. The rotation of the Earth accounts for the apparent daily
rotation of the stars.
6. The apparent annual cycle of movements of the Sun is
caused by the Earth revolving around it.
7. The apparent retrograde motion of the planets is caused
by the motion of the Earth from which one observes.
Copernicus
• Despite the improvement
in the model of the
universe, he still believed
in the idea of retrograde
circular orbits.
• Although the Church condemned the book, the damage
was already done and the world was opened to new was
of thinking about the world.
Galileo
• 1564 to 1642
• Very talented mathematician
• Excellent experimenter and
astronomer
• Originally trained in medicine but
never completed the degree
Galileo
• He was sentenced to house arrest for
the last ten years of his life.
• During that time he wrote his most
complete argument for the
Copernican system.
Galileo: Turning a
Telescope to the Sky
•In 1609, Galileo Galilei became one of the first people to
use a telescope to observe objects in space.
•He discovered craters and mountains on the Earth’s
moon, four of Jupiter's moons, sunspots on the sun, and
the phases of Venus.
Tycho Brahe: A Wealth of Data
•Danish astronomer (1546 to 1601)
•Used several tools to make the most detailed
astronomical observations that had been recorded to
date.
•Brahe favored a modified version of Ptolemy’s theory;
the sun and the moon revolved around the earth and that
other planets revolve around the sun.
•While his theory was not correct, Brahe recorded very
precise observations of the planets and stars that helped
future astronomers.
Tycho Brahe
• Tycho was a great maker of
astronomical instruments.
• He was able to measure the
positions of hundreds of stars
to within 4’.
• He measured the positions of
the planets to within 2’.
Tycho Brahe
• Tycho had devised his
own unique model of the
universe where the
moon and the sun
revolved around the
Earth but all of the
planets went around the
Sun.
• He hoped to use his data
tables to prove his
hypothesis
Tycho Brahe
• Kepler applied to work at
Tycho’s observatory.
• Tycho recognized his talents
quickly and set him to work
with the purpose of finding the
laws of planetary motion.
• Unfortunately Tycho died less
than two years later, before
Kepler worked out his first two
laws. (1601)
Johannes Kepler:
Laws of Planetary Motion
•1609-after much analysis of the Brahe’s data, Kepler concluded that
all of the planets revolve around the sun in elliptical orbits and that the
sun in not the exact center of the orbits.
•Stated his ideas in three laws of planetary motion:
1-the sun is the center of universe and the planets revolve around
it in elliptical orbits.
2-the planets move faster when their orbits bring them closer to
the sun.
3-a mathematical formula used to determine the distance of a
planet from the sun.
•These laws are still used today.
Kepler: Heliocentric with Elliptical
orbits
Area where the
planets moved faster,
because they were
closer to the sun.
Theories of the Universe
Geocentric with Retrograde motion
Heliocentric with Retrograde Motion
Heliocentric with Elliptic motion
Eratosthenes
• 276 BC to 194 BC
• Developed a calendar with a leap year.
• Measured the circumference of the Earth in 325 BC !!
• Achieved an accuracy of about 90% of the actual number.
Isaac Newton
• Law of Universal
Gravitation
• Newton’s great
revelation was that the
same force that pulls an
apple toward the surface
of the Earth is the same
force that holds the
moon in orbit
Isaac Newton: The Laws of Gravity
•In 1687, Isaac Newton showed that all objects in the
universe attract each other through gravitational force.
•The force of gravity depends on the mass of the objects and
the distance between them.
•Newton’s law of gravity explained why all of the planets
orbit the most massive object in the solar system---the sun..
Isaac Newton
•
3 Laws of Motion
1. All objects resist
changes in their state
of motion unless acted
on by an outside net
force (law of inertia)
Isaac Newton
•
3 Laws of Motion
2. If an object is acted on
by an outside net
force, it will accelerate
according to the
following formula
a=F/m
Isaac Newton
•
3 Laws of Motion
3. For every force there
exists an equal and
opposite force
often called
action-reaction law
Isaac Newton
• Newton conducted hundreds of
experiments on light and discovered
the origin of the spectrum created
by prisms
• Newton also
invented the
reflecting
telescope
Historical Figures Assignment:
• As a group assignment you will create a presentation (poster board,
PowerPoint, etc.) in a creative way on your historical figure.
• Your presentation needs to have:
• Facts of the Astronomer
• Their significance
• Originality
You will receive a group grade, however your individual feedback score
will be calculated into your final project grade.