Download The Changing View from Earth

The Changing
View from Earth
Chapter 13
Cartoon of the Day
What our Ancestors Saw
For thousands of years the sky has been
a source of information
Time
Date
Weather
Farmers took their cues from the celestial
bodies (Sun, moon, stars) to know when to
plant, and harvest their crops
Sailors used stars as a guidance system
to cross oceans
Astrologers were in demand
People believed their destinies could be
foretold by the stars.
Ancients used the stars and motion of
planets to
Predict planetary motion, seasons, and
eclipses
Stories from Cultures
• Hindu mythology
– Seven wise men married
seven sisters. Six of the
women divorced their
husbands and moved to
another location in sky. They
became the Pleiades (distinct
star pattern)
Asterism – a distinctive star
pattern
– The seven husbands became
the seven stars of the big
dipper. The wife became
Alcor. A star in the crook of
the big dipper.
Stories from Cultures
• Algonquin, Iroquois, and Narragansett
– saw the constellation Ursa Major as a bear
running away from hunters
– In the fall because the bear is low enough to
brush the trees … the blood from its wounds
turns the leaves red.
• Another legend tells of 3 hunters chasing 4
elk as the 7 stars of the big dipper.
– One hunter is accompanied by a dog
Celestial motion (Lunar)
The moon traces a
westward path across the
sky.
Each night it rises in the
east an hour later than the
previous night
It’s shape appears to
change in phases, waxing
from thin crescent to half
and full moon. Then
waning to a sliver again.
http://www.astro.wisc.edu/~
dolan/java/MoonPhase.ht
ml
Solar Motion
The Sun has no phases
 It also rises earlier and farther north each day from December 22 to
June 22 and sets later
 Through the summer and fall it rises later and set earlier.
– http://www.earth.uni.edu/~morgan/ajjar/Solar
Motion/solarzenith.html
Stellar Motion
Stars and Planets also follow the same
pattern
They rise 4 minutes
Earlier each night
Planetary Motion And Retrograde
Greeks noticed 5 objects wandering
through the stars
Called planets
Mercury, Venus, Mars, Jupiter, Saturn
Venus and Mercury seemed to stay close to the
sun
Mars, Jupiter, Saturn wandered Eastward
Once a year they appeared to go backwards (westward)
Retrograde motion
Retrograde motion is the backwards
motion that planets appear to trace across
the sky.
Modelling Celestial Motion
• Noticing the patterns is only half the battle
– Come up with basic ideas or theories
– Check theories using models
Two early models
Geocentric
Earth centered model
Heliocentric
Sun centered model ( the one accepted today)
Geocentric
Aristotle
Placed stars on outer
circle (firmament or fixed
stars)
Also called the celestial
sphere
Inside the sphere he
arranged more concentric
spheres on which he
placed the Sun, Moons
and planets
Explaining Epicycles
Aristotles model didn’t explain epicycles
Ptolemy created a model which included
an additional level of circles called
Epicycles
Good for predicting astronomical events
Heliocentric
1500’s Nicholas Copernicus
Proposed a new model
Fixed sun
Planets (including Earth rotate around the sun)
Arranged the planets orbits in a solar plane
Imaginary disk extending out the suns Equator
Galileo
Italian Astronomer
Discovered evidence supporting heliocentric
model.
Used a telescope
Saw that Venus had phases like the moon did
Spots on surface of sun
Mountains on the moon
Rings around saturn
Four moons orbiting Jupiter (actually has 16)
Galileo
• Published his ideas in Dialogue
– Galileo was required to recant his heliocentric
ideas, which were condemned as "formally
heretical";.
– He was ordered imprisoned; the sentence
was later commuted to house arrest.
– His offending Dialogue was banned; and in an
action not announced at the trial, publication
of any of his works was forbidden, including
any he might write in the future.
The solution
The answers were discovered by a
German mathematician Johannes
Kepler
According to calculations predictions
would be more accurate if planetary orbits
were ellipses (rather than circles)
Ideas strengthened by Newton’s
Gravitational laws
– All objects in the universe are attracted to
one another
New Planets
In 1781 Uranus was discovered
Later using sun-centered model and
Newton’s laws they predicted where
another planet should be
Pointed their telescopes in it’s direction
and discovered Neptune.
Now knew of 8 planets in total
(missing Pluto)
Today’s Views
• Scientist constructed geocentric model based on
observations with unaided eye
• When Ideas were challenged a new theory was
formulated
• This process of formulating new ideas continues
even today.
• Thanks to technology we now have information
on solar system, sun, 9 planets and their moons,
meteors, asteroids, comets
The Sun
Made of Hydrogen gas
• Diameter 1.4 million km (110 times earth)
• Surface is constantly writhing/churning
Solar prominance
Streamers of hot gas that arch into space.
Cooler regions appear darker in color
(Sunspots)
Near them violent outbursts/eruptions occur –
Solar flares
Solar flares send high energy subatomic
particles into space. (creates solar wind which
can affect Earths activities)
The Sun
330,000 times more massive than earth
Hydrogen and helium
Three layers
Core – 15,000,000 ۫ C
Photosphere – region of suns light
6,000 ۫ C
Corona
1,000,000 ۫ C
Closest star to the Earth
Because Sun has planets orbiting it
scientist predict other stars might have
planets orbiting
The Planets
Inner planets
Mercury, Venus, Mars
Called terrestrial planets
Because of their rocky composition
Outer planets
Jupiter, Saturn, Uranus, Neptune
Have a gaseous composition
Pluto
Class all by itself because of strange orbit
and tiny size
Scale
Earth diameter = 12,750 km (1 EarthDiameter)
• Venus = 12,100 km (0.95 Earth-diameter)
• Jupiter = 11.2 Earth-Diameter
– 143,200 km / 12,750 km = 11.2
Scale
• Other scales measured
– Mass
– Density
– Rotational period (time around sun)
– Orbital period
Measuring Distance
Distances in astronomy are so immense
they are “astonomical”
Scale used = astronomical units (AU)
1 AU = average distance from Earth to sun
(149,599,000 km)
– Mars distance = 1.5 AU
• Why is AU expressed as an average
distance?
Other Solar System Bodies
Asteroids
Known as minor planets (1m – 100’s of km)
– Cere’s 1000 km
Irregular shaped bodies of rock (silicate)
Some cross path of earth (potential Collision)
Comets
Made of dust and ice
Orbit at large distances
Some fall towards the sun (evaporate) form tails
Meteors, and Meteorites
Dust and rock particles that heat up an vaporize in
earths atmosphere (shooting stars) - Meteors
Some remain large enough to hit the earth Meteorites