Topic 3:
Earth In the Universe
Electromagnetic Energy
• Celestial objects – any object
outside Earth’s atmosphere
Electromagnetic Energy
• Electromagnetic Energy – energy
that is given off from all objects not
at absolute zero (0K or -273oC)
Type of EM depends on wavelength of
energy
Electromagnetic Energy
• Electromagnetic Spectrum – model
that shows all the types of EM in
order according to wavelength
(ESRT pg 14)
Electromagnetic Energy
Electromagnetic Energy
• Each element emits energy in
specific wavelengths
We can tell what elements celestial
objects are made of by looking at the
wavelengths that they emit
Example: Mercury
4
5
6
7
Doppler Effect
• Doppler Effect – when the EM
wavelengths given off by an object
change because the object is
moving
Doppler Effect
Red shift – when the object is moving
away
 Causes the wavelengths to get
longer
 Spectral lines move closer to the red
end of the spectrum
– Pattern of lines remains the same
Doppler Effect
4
5
6
7
Doppler Effect
Blue shift – when the object is getting
closer
 Causes the wavelengths to get
shorter
 Spectral lines move closer to the blue
end of the spectrum
– Pattern of lines remains the same
Doppler Effect
Origin of the Universe
Origin of the Universe
• Universe – everything that exists in
any place
Over 10 billion years old and up to 13.7
billion years old
Origin of the Universe
• Big Bang Theory – states that all
matter and energy started out
concentrated in a small area and
after a big explosion matter
organized into atoms
Matter eventually organized into
celestial bodies
Matter continues to expand in all
directions (pg 39 Fig. 3-1)
Evidence for the Big Bang
• Background Radiation
There is energy left from the initial
explosion coming from all directions in
the universe
 Found as microwaves
Evidence for the Big Bang
• Doppler Effect (Red Shift)
We see that the spectral lines shown by EM
energy emitted by other galaxies are shifted
toward the red end of the EM spectrum

This means  EM wavelengths given off by
galaxies are lengthening

This means  Galaxies are moving away

This means  The Universe is expanding
– Objects in the universe are moving
away from each other
Evidence for the Big Bang
• Doppler Effect
 Objects in the universe continue to move away
from each other as a result of the initial Big Bang
explosion
Structure of the Universe
• Most of the universe is empty space
• Distances between objects in the universe are so
large that the unit used to measure distance is a
light-year
Light-year – the distance light will travel in a
vacuum in one year
 1light-year = 9,460,730,472,580.8 km
(9.5x1012km) or 5,878,625,373,183.608 miles
(5.9x1012mi)
• Organized matter in the universe forms:
Galaxies
• A galaxy is a collection of billions of
stars, etc. held together by gravity
Average galaxy has over 100 billion
stars
There are over 100 billion galaxies
Galaxies are classified by shape
 Elliptical, irregular, spiral
Galaxies
Our solar system is in the Milky Way
Galaxy
 The Milky Way Galaxy is spiral shaped
(pg 41, Figure 3-3)
Stars
• A star is a large ball of gases held
together by gravity
Stars produce large amounts of energy
and shine
Stars
• Energy Production
Energy released by stars is produced
by nuclear fusion in their cores
Nuclear fusion – where smaller atoms
combine to make larger atoms
Only occurs under VERY high
temperature and VERY high pressure
within the core of the stars
Energy produced is radiated as EM
energy
Stars
• Star Classification
Stars are classified by
Temperature/Color and Luminosity/Size
ESRT pg 15
Stars
Star Types
Most stars
Average Size
As temperature increases,
Main
Sequence luminosity increases
Examples:
Sun, Alpha Centauri, Sirius,
Barnard’s Star, Proxima Centauri,
Spica
Star Types
Large
High luminosity, low temperature
Giant
Late stage of small – medium sized
star
Examples:
Pollux, Aldebaran, Polaris
Star Types
Massive
Very high luminosity, low temperature
Super
Giant
Late stage of a big star
Examples:
Rigel, Deneb, Betelgeuse
Star Types
Small
Low luminosity, high temperature
White
Dwarf
Last shining stage of small – medium
sized star
Examples:
40 Eridani B, Procyon B
Star Types
Dead star
Black
Dwarf
No more fusion = not much EM
energy
Distance to Other Stars
• Distance to other stars:
Alpha Centauri = 4.2 ly
Barnard’s Star = 6.0 ly
Sirius = 8.6 ly
Polaris = 430 ly
Betelgeuse = 640 ly
Rigel = 860 ly
Life of a Star
Solar Systems
• A solar system is a star with objects
orbiting around it
Our Solar System
Our Solar System
• Solar system(ours) – the sun and all
objects that orbit the sun
Parts of the Solar System
• Satellite – any object that revolves
around another object
The Earth is a satellite of the sun
The moon is a satellite of the Earth
Parts of the Solar System
• Planets
Largest satellites of
the sun
There are 8 planets
orbiting the sun
Parts of the Solar System
• Asteroids
Rocky, mostly irregularly shaped
objects that orbit the sun
 Most between Mars and Jupiter
Parts of the Solar System
• Moons
A body that orbits a planet or an
asteroid
Parts of the Solar System
• Comets
A “dirty snowball” orbiting the sun
Main body is solid, tail is gases
produced as heat from the sun
vaporizes main body
Parts of the Solar System
• Meteroids
Small solid fragments that orbit the sun
Meteor – a meteoroid that passes
through the Earth’s atmosphere
 Meteorite – a meteor that lands on
Earth
 Impact crater – depression in Earth’s
surface caused by a meteorite
Evolution of the Solar System
• Our solar system is about 5 billion
years old
• The death of a star caused debris
(gas and dust) to be thrown into
space
• Matter from the cloud starts to pull
together into a center and spin
• The large amount of matter in the
center begins nuclear fusion = sun
Evolution of the Solar System
• Outlying matter forms clumps in ring
around sun
Heavier elements stay closer to sun,
lighter elements blown further outward
Becomes planets, moons, asteroids,
etc.
Evolution of the Solar System
• Heat produced by gravity, friction,
etc causes planets to melt
Planets layered based on density while
in this liquid stage
• Terrestrial planets harden into solid
planets known today
Evolution of the Solar System
Evolution of the Solar System
• http://www.antares-
fulldome.com/film/birth-solar-system
Evolution of the Solar System
Characteristic
Which planets?
Distance from Sun
Size (relative)
Composition
Density
Number of moons
Other features
Terrestrial
Jovian
Motion of the Planets
• Our solar system spins with Milky Way
Galaxy
One trip every 225 million years
Rotation
• Rotation – spinning on an imaginary
axis
Period of rotation = the time it takes for
a planet to spin on its axis once =
length of that planets day
You can tell planets spin because their
surface features move
Revolution
• Revolution – movement of a planet
around the sun in its orbit
Orbit = path that a planet follows as it
travels around sun
Period of revolution = the time it takes
for a planet to make one trip in its orbit
around the sun = the length of that
planet’s year
Planets revolve around the sun
counter-clockwise if watching from
Polaris
Planetary Orbits
• Orbits are shaped like an oval,
called an ellipse
• Ellipses have two points in the
middle called foci (singular = focus)
The sun is one of the foci in all planets’
orbits
• The major axis is the straight line
distance from one side of the ellipse
to the other passing through both
foci
Planetary Orbits
Major Axis
Eccentricity
• Eccentricity = how oval an ellipse is
Measured using a formula
 Eccentricity of an ellipse = distance between the foci
length of the major axis
Eccentricity of a circle = 0
 Eccentricity of a line = 1
– All ovals fall between 0 and 1
Earth’s orbit: page 50, Figure 3-11
 To scale it appears to be a circle

Eccentricity
Eccentricity of ellipse above:
Distance from Sun and Apparent Solar
Size
• The sun is one of the foci for all
planet orbits
• This means that the actual distance
between the sun and each planet
varies throughout the year
NOT what causes the seasons
Distance from Sun and Apparent Solar
Size
• The sun will appear larger when
Earth is closest to sun in its orbit (Jan
3)
• The sun will appear smaller when
Earth is furthest from the sun in its
orbit (July 4)
Principles of Motion and Orbits
• Planets stay in their path around the
sun due the balance of two main
principles of motion
Inertia – an object at rest will stay at
rest or an object in motion will stay in
motion – same direction, same speed –
until another force acts on the object
Principles of Motion and Orbits
Gravitation – force of attraction
between all objects
 Strength of gravitation between two
objects depends on the combined
mass of the objects and the distance
between the objects
– Greater mass = greater gravitation,
lesser mass = less gravitation
– Closer together = greater gravitation,
further apart = less gravitation
Principles of Motion and Orbits
• Actions of both keep planets in orbit
Inertia would keep planet going in
straight line
Gravity pulls planet toward sun
 Curves planet’s path in its orbit
Principles of Motion and Orbits
Principles of Motion and Orbits
• Orbital speed – how fast a planet
travels in its orbit
Depends on the planet’s distance from the
sun
 When a planet is closer to the sun it moves
faster in its orbit
– More gravity
 When a planet is further from the sun, it
moves slower in its orbit
– Less gravity