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The Earth in the Universe
The Universe
• The universe is made up of many
• Galaxies are made up of many stars.
• Some stars have planetary systems
similar to our solar system.
• Earth is a satellite planet of one
particular star…. our Sun.
Where is our solar system
• Our solar system is located in the Milky
Way Galaxy.
• The Milky Way is part of a cluster of
about 30 other galaxies.
Building Our Milky Way
• The central bulge is at the center.
• Spiral arms are around the central
bulge. They contain mostly blue stars,
gas and dust.
• The Earth is located in one of the spiral
• There are blue stars and red stars in
our galaxy.
• Blue stars are young and hot stars.
• Red stars are old and cool stars.
Where is the Earth located?
• Earth is the 3rd planet from the Sun in
our solar system.
Is the Earth Round?
• Technically, Earth is an oblate spheroid.
• It is wider at the equator than at the
• This is caused by the rotation of the
Earth on its axis.
Earth’s Axis
• The Earth’s axis is
an imaginary line
that runs through
the center of the
Earth from the
north pole to the
south pole.
• The Earth is “tilted”
with relation to this
imaginary line 23.5⁰
Earth’s Rotation
• One rotation about
the Earth’s axis
takes 24 hours. This
is called a day.
• Rotation about the
Earth’s occurs from
west to east.
(Counter clockwise)
• Earth’s rotation is
the cause for day
and night.
What happens when the direction
of the axis changes?
• The change in the
direction of the Earth’s
axis is called precession.
• The angle remains the
• This will affect the stars
near the poles
• Does not change the
seasons as long as the
23.5⁰ tilt stays the same.
• The “wobble” about the precessional
axis is called nutation.
• Nutation is a change in the in the angle
of tilt by ½ ⁰ one way or the other.
Results in the tilt either being 23⁰ or
• This occurs over an 18 year period.
• This is due to the Moon.
• This causes a slight change in the
• A barycenter is the
point between two
objects where they
balance each other.
• Its kind of like the
center of gravity.
• The center of
gravity is the point
in the middle of all
the material that
makes up an object,
Center Point of Gravity and
• When a moon orbits a planet, or a planet
orbits a star, both bodies are orbiting
around a point that lies outside the
larger body.
• The moon does not orbit the exact
center of the Earth, but a point about
1710 km below the Earth’s surface.
• The sun is not stationary in the solar
system. It moves as the planets tug on
it, but it never gets too far from the
solar system barycenter.
Planetary Orbits and
Kepler’s Law
• Johannes Kepler was a German
mathematician, astronomer and
• He was a key figure in the 17th century
scientific revolution.
• Kepler’s Laws describe the motion of
the planets around the sun.
• Kepler knew of 6 planets: Earth, Venus,
Mercury, Mars, Jupiter and Saturn.
Kepler’s First Law
• States that planets move around the
sun in ellipses, with the sun at one
• What does this really mean?
– This means that the distance between the
planet and the sun varies, as the planet
goes around.
Kepler’s Second Law of Planetary Motion
Each planet moves around the Sun so that an imaginary line
joining the planet and the Sun will sweep over equal areas in time
This means that because the orbits are elliptical,
the planet’s travel at different speeds at different
positions in the orbit.
(a) The planet’s position in it’s orbit where it is closest to
the Sun.
(b) The speed is fastest at perihelion
(a) The planet’s position in it’s orbit where it is farthest from
the Sun.
(b) The speed is slowest at aphelion
Earth’s Orbit
Kepler’s Third Law of Planetary Motion
The farther a planet
is from the Sun, the
longer it takes to
make one complete
The Sun
Parts of the Sun
• The sun has a core, a
radioactive zone, and a
convective zone.
• The sun is composed of
gas and has no solid
• The two gases that make
up the sun are hydrogen
and helium.
• Compared to other stars,
our sun is medium sized
and has a medium
temperature. However,
it is still VERY hot!
Producing Energy
• Gravity pulls all of the mass
inward, creating intense pressure.
• The pressure is high enough to
force 2 atoms of hydrogen to
fuse into an atom of helium
• Heat is released during this
reaction and so is radiation (in all
parts of the electromagnetic
spectrum). This radiation strikes
Earth, helping heat the
atmosphere, drive our weather,
and provide energy for life.
Solar Wind Protection
• The Earth is
protected from the
solar wind by it’s
magnetic field which
extends from the
How does the Sun support life on
• Photosynthesis is the
process by which green
plants and other
organisms make their
own food.
• Green plants take in
carbon dioxide, water
and sunlight and
produces oxygen while
making their food.
Differentiated Heating by the
• As the Earth moves
around the sun, different
parts of the Earth get
different amounts of solar
• The tropics get more solar
radiation than the poles,
so it is warmer there year
Sun and Seasons
• The Earth’s movement around the Sun is
called a revolution.
• The revolution and the tilt are the main
causes of the seasons.