Download Topic 3 Earth in the Universe

Topic 3
Earth in the Universe
Rotation vs. Revolution
Rotation: an object spinning on its axis
Revolution: an object orbiting around another object or
point in space
A Survey of the Solar System
Geocentric vs. Heliocentric
Improving the heliocentric model
• Galileo saw Venus experience phases like the
Moon and saw satellites orbiting Jupiter
Isaac Newton’s Law of Universal
Gravitation
The force of attraction between two objects is greater with
increased masses of the objects and less with increased distance
between them.
Kepler’s
Laws of Planetary Motion
1. The orbital paths of the planets are
elliptical, with the Sun at one focus
SHAPE OF ELLIPSES
Eccentricity = 0
circle
Eccentricity = 0.5
Eccentricity = 1
line
• TO THE HUMAN EYE, MOST ORBITS OF
PLANETS LOOK LIKE CIRCLES
• SLIGHTLY ELLIPTICAL SHAPE OF EARTH’S ORBIT
CAUSES THE PLANET TO VARY THE DISTANCE
TO THE SUN DURING REVOLUTION
147 million
kms.
152 million kms.
Gravitational Effects of Varying the
Distance to the Sun
Gravitation force influenced
by mass and distance
1. Greater the mass = greater the gravitational
attraction
2. Closer the 2 objects = greater the gravitational
attraction
Perihelion = greater gravitational attraction
Aphelion = less gravitational attraction
Mass stays the same but distance varies causing gravitational
attraction to vary
If gravitational attraction varies, velocity will vary
Perihelion = faster velocity
Aphelion = slower velocity
Appearance of Sun Changes with Varying
Distance
Terrestrial Observations that support
the Heliocentric Model
1. Foucault Pendulum
1. Evidence of Earth’s Rotation
• 1851, Foucault’s pendulum will appear to change in a
predictable way.
• Why is this evidence? There is no force acting on
the pendulum to make its plane of oscillation rotate
or go around its own axis
• It would continue to swing in the original path if
Earth did not rotate.
No force that makes pendulum rotate – must be
earth that is rotating!!!
2. Evidence for Rotation
• Coriolis Effect – the tendency of objects moving over the
earth (air, water, planes, projectiles) to be deflected (curve
away) from a straight line path. The French scientist, Gaspard
Coriolis, first explained the deflection of objects moving over
the surface due to Earth’s rotation
• The deflection is to the right in the Northern Hemisphere and
to the left in the Southern Hemisphere.
• This deflection occurs because Earth’s surface is rotating with
respect to the objects.
Planetary Orbits and Rotation
Tipped over by
more than 900
Mercury and Pluto: Unusually highly inclined orbits
Two Kinds of Planets
Planets of our solar system can be divided into
two very different kinds:
Terrestrial (earthlike) planets:
Mercury, Venus, Earth, Mars
Jovian (Jupiter-like) planets: Jupiter,
Saturn, Uranus, Neptune
Size of Terrestrial Planets Compared to
Jovian Planets
Terrestrial
Planets
Four inner
planets of the
solar system
Relatively small in
size and mass (Earth
is the largest and
most massive)
Rocky surface
Surface of Venus can not be seen
directly from Earth because of its
dense cloud cover.
The Jovian Planets
Much larger in mass
and size than
terrestrial planets
Much lower
average density
All have rings (not
only Saturn!)
Mostly gas; no
solid surface
Space Debris
In addition to planets, small bodies orbit the sun:
Asteroids, comets, meteoroids
Asteroid
Eros,
imaged by
the NEAR
spacecraft
The Asteroid Belt
Most asteroids
orbit the sun in a
wide zone
between the orbits
of Mars and
Jupiter.
(Distances and times reproduced to scale)
Comets
Icy nucleus, which evaporates
and gets blown into space by
solar wind pressure.
Mostly objects in highly elliptical orbits,
occasionally coming close to the sun.
The tail of a comet always
points away from the Sun.
Meteoroids
Small (mm – mm sized)
dust grains throughout the
solar system
If they collide with Earth,
they evaporate in the
atmosphere.
Visible as streaks of light
(“shooting stars”):
meteors.
THE SOLAR SYSTEM
HELIOCENTRIC
100,000 light- years
less than 0.01 light years
THE UNIVERSE  THE GALAXY  THE SOLAR SYSTEM  THE PLANET
Going beyond our solar system……
The stars appear to rise and set because
the Earth rotates beneath them
The complete circular path can be
seen for stars in the northern part
of the sky around Polaris
Circumpolar constellations
never set.
Circumpolar constellations
change with latitude… sky
changes with latitude
Brightness of Stars
Absolute magnitude/luminosity: the actual amount of light
given off by a star
Apparent magnitude: the amount of light given off by a star AS
SEEN FROM EARTH
.
Light year: the distance light travels in one year
= 9.5 trillion km
(light travels 300,000 km/sec)
Star Life Cycle: Stars are like humans. They are
born, live and then die.
• Nebula – cloud
of gas and dust
Protostar – new, just
forming star
Stars start from clouds
Clouds
provide the
gas and dust
from which
stars form.
But not this kind of dust
Rather: Irregular Grains
Of Carbon or Silicon
At 15 million degrees Celsius in the center
of the star - nuclear fusion begins
Star Formation
Stars exist because of gravity
Two opposing forces in a star are
• Gravity – contracts
• Nuclear fusion – expands
A Balancing Act
Energy released from nuclear fusion counteracts inward force of gravity.
Throughout its life, these
two forces determine the
stages of a star’s life.
Star’s Life Cycles
Hertzsprung-Russell Diagram
aka Luminosity and Temperature of Stars
Diagram – NOT A MAP
DIAGRAM IS A USEFUL WAY TO FOLLOW
CHANGES THAT TAKE PLACE AS THE STARS
LIVE OUT THEIR LIVES
Diagram is made by plotting (graphing) each
star's LUMINOSITY (brightness) and
TEMPERATURE (as reflected by color)
COMPARED TO THE SUN
Most stars are on the Main Sequence because
that is where they spend most of their lives
Our sun is an
average main
sequence star
Luminosity of 1
Temperature
5500°C – yellow
in color
Classifying Stars based on luminosity and
temperature
Schematically, stars fall into regions shown
below with respect to the sun.
All planets compared to Our Sun
No longer
considered a
planet
Hertzsprung-Russell Diagram
Star Evolution
• Giants (or red giants)
• Very luminous (These stars are enormously bright for
their temperature due to their size (10x size of sun)
• Low Temperature
• Represent the late evolution of medium-sized main
sequence stars when they greatly expand in size
Hertzsprung-Russell Diagram
Star Evolution
• Super Giants (100 to 1,000 times diameter of
sun)
• Only a few percent of all stars
• They represent the late evolution of stars
more massive than the sun.
• Usually explode in a supernova event
H-R Diagram – Star Evolution
White dwarfs
•Small (approximate the size of
Earth)
•Hot
•Low in luminosity (due to their
small size)
Black dwarfs – dead stars
THE SOLAR SYSTEM
HELIOCENTRIC
100,000 light- years
less than 0.01 light years
THE UNIVERSE  THE GALAXY  THE SOLAR SYSTEM  THE PLANET
THE GALAXY
• The Milky Way Galaxy
– Over 100 billion stars in our galaxy
– The Sun = 1 of those stars
THE SUN
(Our
Solar System)
100,000 light years
Speed of Light = 670,616,700 mph
UNIVERSE = THE BEACH
GALAXY = GRAIN OF SAND
THE UNIVERSE  THE GALAXY  THE SOLAR SYSTEM  THE PLANET
The structure of the Universe
A galaxy is a collection of billions of stars held
together by gravity
The universe contains
billions of galaxies
and each galaxy
contains billions of
stars.
Our galaxy is a spiral
galaxy called the
Milky Way
CLUSTERS OF GALAXIES
• Many times galaxies are seen in clusters
• Our Galaxy is found in a cluster
GALAXY
THE UNIVERSE  THE GALAXY  THE SOLAR SYSTEM  THE PLANET
THE UNIVERSE
• The Universe
– everything that physically exists
– contains billions of galaxies
Clusters of Galaxies
THE UNIVERSE  THE GALAXY  THE SOLAR SYSTEM  THE PLANET
Big Bang theory – Origin of the Universe
Big Bang marks the inception of the universe
• Occurred about 15 billion years ago
• All matter and space was created
Not a huge explosion that hurled matter in
all directions. Technically, there was no
“bang”
Technically, matter is not moving outward in
all directions. Reality: space expands
Origin of the Universe
Big Bang Evidence
• More distant galaxy – moving WITH space as
space itself expands
• Think loaf of unbaked raisin bread. The raisins
are galaxies and the dough is space
Raisin bread analogy of an expanding
universe
Expansion Evidence
 Stars are made of elemental gases that emit
specific wavelengths within the electromagnetic
spectrum based on their chemical composition. Each
gas emits certain wavelengths that are unique to that
element.
 The combination of a star’s elements which
produce a pattern of spectral lines can be used to
identify the star rather like a fingerprint or bar code.
 Spectral lines are lines that correspond to various
wavelengths seen in an element’s spectrum.
Red Shift – Blue Shift
In 1929, Edwin Hubble observed that spectral lines emitted
by stars in distant galaxies were considerably Red shifted.
The spectral lines (fingerprint or bar code) of stars coming
towards Earth were shifted to the blue light end of the
spectrum (shorter wavelength)
The spectral lines (fingerprint or bar code) of stars going
away from Earth were shifted to red light end of the
spectrum (longer wavelength)
Shifting of Wavelengths is called the
Doppler Effect
• Change in the wavelength of
light emitted by an object due
to its motion
• Movement toward “squeezes”
the wavelength
• Shorter wavelength
• Light shifted toward the blue
end of the spectrum
• Movement away stretches the
wavelength
• Longer wavelength
• Light shifted toward the red
end of spectrum
RED SHIFT – BLUE SHIFT
• The greater the degree of shift of the spectral lines,
the faster the object is moving away
• The star light DOES NOT appear red or blue (it still
appears as white light from the star)
• The “bar code” for each element either shifts to the
shorter wavelength blue end of the spectrum or to
the longer wavelength red end of the spectrum
What is the best
inference that can be
made concerning the
movements of Galaxies
A, B, and C?
Other Evidence for Big Bang
• Energy created by big bang expanded along with matter
• Should be radiation all over the universe mixed in with energy
given off by stars
• Evidence of long wavelength background radiation (actually
microwaves) appear to be coming from all directions in the
universe
• Background radiation was discovered in 1964 by Arno Penzias
and Robert Wilson, who later won the Nobel Prize for this
discovery