Transcript Ancient Astronomy - Mrs. Petersen`s Earth Science

Ancient Astronomy
Ancient Astronomy
• Why were ancient people
interested in astronomy
– To keep time
– To determine when to plant and
harvest crops
– For navigation
– For religious purposes
• A big challenge was to
understand the systematic
and repeating changes that
occur in the sky.
Ancient Astronomy
• Every day:
– The sun rises in the east and sets in the west.
– More or less, the pattern of sun motions is the same every
day
– The pattern of the stars were the same every year.
• But note that
– The period of time that the sun is above the horizon is not
always the same (longer v. shorter days)
– The sun is higher in the sky at noon during some parts of the
year
– The exact point along the horizon at which the Sun rises or sets
varies throughout the year
– Different star clusters (constellations) rose and fell at different
times during the year.
A star that all
other stars pivot
W
N
Here’s what they saw in the North
E
Celestial N. Pole
Here is their thoughts
There was a crystal celestial sphere
up in the sky with stars affixed to it.
Stars are fixed on
celestial sphere
Celestial Equator
Question is – are we rotating or
are the stars, sun & planets on
the celestial sphere rotating?
Celestial S. Pole
How could you tell?
Celestial Sphere is an extension of our globe
Celestial N. Pole
The Other Ultimate Question is
with all of this moving stuff - where
are we in the midst of all this?
Stars are fixed on
celestial sphere
How can you figure out that too?
Celestial Equator
Celestial S. Pole
Celestial Sphere is an extension of our globe
Ancient Astronomy
• Ancient Astronomers:
– Thought that the stars and everything in the
heavens revolved around us and that we were
the center of the universe because everything
else seems to be moving, and we were
stationary.
• Today’s lesson is about the evolution of
astronomical thought & theory.
Greek Philosophy & Theory
• Universe was perfect
– God was perfect
• Earth was at center
– Earth was the footstool &
Gods creation
• Inside rotating dome
– (celestial sphere)
• Introduced Geocentric
Model
Why do you think they thought this way?
Earth at the Center
• In a geocentric system, Earth is at the
center of the revolving planets and stars.
Basic assumptions:
• Planets move at uniform speeds
• Planets move on circular paths
•We couldn’t be moving –
otherwise there would be a great
wind.
Ask students to describe the movement
of Earth and the other planets in the
geocentric system. (Earth is stationary;
the other planets revolve around Earth.)
Ptolemy’s Model
• Noticed retrograde motion
If the heavens were perfect, and all the planets were on perfect
circles, how could you then explain retrograde motion?
• Introduced epicycles
Ptolemy’s Model
Clip: Geocentric Motion
Copernican Revolution
• 1543 – Nicolaus Copernicus
• Able to work out the arrangement of the known
planets and how they move around the sun.
Developed the Heliocentric model based on
Ancient Greek Observations.
• Many didn’t accept it – needed more evidence.
Heliocentric Model
• In a heliocentric system, Earth and the
other planets revolve around the sun.
Retrograde Motion Explained
• Geocentric
System:
• Heliocentric
System:
Copernican Revolution
• Several other astronomers provided
further evidence for the Heliocentric
Model:
– Galileo
• (1564 – 1642)
– Tycho Brehe
• (1546 – 1601)
– Johannes Kepler
• (1571 – 1630)
Galileo’s Evidence
• 1610 Galileo used the newly invented
telescope to make discoveries that
supported the heliocentric model.
Galileo’s Evidence
• Moon had scars & dimples.
– Not everything in the heavens were perfect.
Galileo’s Evidence
• The sun had spots
– Again, not everything in the heavens were
perfect.
Galileo’s Evidence
• With his telescope, he discovered:
– Four moons around Jupiter
• Proved that Not everything revolved around the
earth.
Galileo’s Evidence
• Venus had phases
– Couldn’t get that with w/ a geocentric model.
Galileo’s Evidence
• Catholic Church
considered it
heresy.
• Galileo was jailed
and later put under
house arrest in
1633
Tycho Brahe’s Observations
• He and his assistants
made much more
accurate observations
concerning the motion of
the planets for more than
20 years.
Kepler’s Calculations
•
•
•
•
Tycho’s Assistant
Analyzed the years worth of observations
Used math to explain motion of the stars.
Noticed that the planets do not move in
perfect circles, but rather elliptical.
Newton & Hooke
Gravity is what governs all
of the motion in space.
Einstein
Explains Mercury’s Orbit
Gravity & the Fabric of Space (& Time)
Explains bending of light
Modern Discoveries
• Today, we know that the solar system
consists of the sun, eight planets and their
moons, and several kinds of smaller
objects that revolve around the sun.
Modern Discoveries
• Galileo used a telescope to observe the
solar system – as do astronomers today.
• Modern Day astronomers use a series of
different telescopes to gain a better view
of the universe.
• Space Program
– Space probes, men on moon etc.
The Speed of Light:
light travels at a speed of
186,000 miles a second or 700
million miles an hour. For scale,
the distance from the Earth to
the Moon is about 239,000
miles. This seems pretty fast and
indeed theory says that nothing
can travel faster than the speed
of light.
In our every day lives light
seems to travel from one place
to another instantaneously.
When we flip on the light in a
room there is no delay between
when we first see the bulb start
glowing and when light
illuminates the far corners of the
chamber. Our nervous systems
are much too slow to notice the
rays of light that appear from the
bulb and move like a wave
washing over the room.
When we deal with the immense
distances of space, though, even light
seems slow. When astronauts were on
the Moon it took over a second for the
radio waves (which travel at the speed
of light) carrying their voices to reach
us. Light coming from the sun takes
eight and one half minutes to hit Earth.
(This means that if the sun were
suddenly to go dark, it would take over
eight minute for us to notice) Light from
the nearest stars, other than the sun,
takes four and a half years to get here.
From the farthest stars in distant
galaxies it can take billions of years for
the light to arrive..
The distance light can travel in a year is called a "light year." The light year is
one of the basic measures of distance for astronomy.
When designing probes for trips to other planets in our solar system it is
important for the planners to keep the communications time lag, caused by the
speed of light, in mind. For example, a probe designed to land on Mars must be
smart enough to handle problems in the flight on it's own without instructions
from Earth. If a course change is needed during landing the probe would have
to do it automatically. The delay caused by the probe requesting instructions
from Earth and getting commands back might be nearly an hour, plenty of time
for the probe to crash.
The delay caused by the speed of light can sometimes be noticed here on
Earth during telephone calls. Long distance calls that have been routed over
one or more space satellites may cause a half second or so delay between the
speaker and the listener.
The distance light can travel in a year is called a "light year." The light year is
one of the basic measures of distance for astronomy.
When designing probes for trips to other planets in our solar system it is
important for the planners to keep the communications time lag, caused by the
speed of light, in mind. For example, a probe designed to land on Mars must be
smart enough to handle problems in the flight on it's own without instructions
from Earth. If a course change is needed during landing the probe would have
to do it automatically. The delay caused by the probe requesting instructions
from Earth and getting commands back might be nearly an hour, plenty of time
for the probe to crash.
The delay caused by the speed of light can sometimes be noticed here on
Earth during telephone calls. Long distance calls that have been routed over
one or more space satellites may cause a half second or so delay between the
speaker and the listener.
The speed of light has several properties which may seem
counter-intuitive to us, but are true:
-Nothing travels faster than the speed of light.
-No matter how fast you are moving the speed of light
seems to be the same speed as if you were not moving
at all.
-As an object or person is accelerated toward the speed
of light time slows down for it/him.
This last property leads to the "twins" effect: Twin brothers
live on Earth. One brother takes a trip to a distant star
traveling at a high percentage of the speed of light. When
the twin returns he will be younger than his brother because
for him time slowed down during the trip.
This effect, called "time dilation," helps explain why the
speed of light is the same no matter how fast you are going.
As a traveler accelerates time slows down for him. This, in
turn, affects his measurements.