Download Earths Motion

Astronomy
EEn.1.1 Explain the Earth’s role as a
body in space
Astronomy: Part 1
EEn.1.1.1 Explain the Earth’s motion through
space, including precession, nutation, the
barycenter and its path about the galaxy.
Big Bang Theory
• Hubble’s Law (1920’s) – All other galaxies
objects of the universe are moving away from
our galaxy
• Redshift vs. Blueshift?
– https://www.youtube.com/watch?v=th_9ZR2I0_w
&index=95&list=PL908547EAA7E4AE74
How The Universe Came To Be…
• The Big Bang Theory
• Scientists believe that everything in the
universe was together compressed as an
infinitely small volume
• 15 billion years ago in an explosive
moment, the small volume began
expanding at and incredible rate
– In moments, the universe was already the size
of the solar system
Big Bang Theory Continued
• After thousands of years of EXPANDING and
cooling, matter was able to combine into
separate entities forming galaxies and stars
• Our Sun was created from a nebula
– A swirling cloud of gas and dust
– With the force of gravity, the cloud began
collapsing on itself
– The temperature increased to the point where
nuclear reactions could occur- this is the birth
of our Sun
Nebular Hypothesis
• Kant and Laplace (1800’s)
– Theory that our Solar System originated from the
collapse of a Nebula
– http://csep10.phys.utk.edu/astr161/lect/solarsys/
nebular.html
Formation of Our Solar System
Formation of Our Solar System
• Astronomers use Earth-based observations and data
from probes to derive theories about how our solar
system formed.
• The significant observations related to our solar system’s
formation include the shape of our solar system, the
differences among the planets, and the oldest planetary
surfaces, asteroids, meteorites, and comets.
How did our Solar System form?
A Collapsing Interstellar Cloud
• Stars and planets are formed from clouds of gas and
dust, called interstellar clouds or a nebula.
• The interstellar clouds consist mostly of gas, especially
hydrogen and helium that often appear as blotches of light
and dark.
• Many interstellar clouds can be observed along the Milky
Way in regions that have relatively high concentrations of
interstellar gas and dust.
A Collapsing Interstellar Cloud
• Our solar system may have begun when interstellar gas
started to condense as a result of gravity and became
concentrated enough to form the Sun and planets.
– The collapse is initially slow, but it accelerates and the cloud soon
becomes much denser at its center.
– Rotation slows the collapse in the equatorial plane,
and the cloud becomes flattened.
– The cloud eventually becomes a rotating disk with a dense
concentration at the center.
Sun and Planet Formation
• The disk of dust and gas that formed the Sun and
planets is known as the solar nebula.
• The dense concentration of gas at the center of this
rotating disk eventually became the Sun.
• In the disk surrounding the Sun, the temperature varied
greatly with location.
• As the disk began to cool, different elements and
compounds were able to condense depending on their
distance from the Sun which impacted the compositions of
the forming planets.
Formation of Our Solar System
Sun and Planet Formation
Merging into Planets
– Jupiter was the first large planet to develop in the outer solar system.
– As its size increased, its gravity began to attract additional gas, dust,
and planetesimals.
– As each gas giant acquired material from its surroundings, a disk
formed in its equatorial plane, much like the disk of the early solar
system.
– In the disk, matter coalesced to form satellites.
Formation of Our Solar System
Sun and Planet Formation
Merging into Planets
– The inner planets also formed by the merging of planetesimals.
– These planetesimals were composed primarily of refractory
elements, so the inner planets are rocky and dense.
– The Sun’s gravitational force is theorized to have swept up much of
the gas in the area of the inner planets, preventing them from
acquiring much additional material.
– The inner planets initially ended up with no satellites.
Formation of Our Solar System
Sun and Planet Formation
Debris
– The amount of interplanetary debris thinned out as it crashed into
planets or was diverted out of the solar system.
– The planetesimals in the area between Jupiter and Mars, known as
the asteroid belt, remained there because Jupiter’s gravitational force
prevented them from merging to form a planet.
Formation of our Solar System
• Once our Sun was born…
• The dust particles in our galaxy began to combine to
form clusters
• The clusters stick together to form rocks
• Accretion occurs- gravity causes the rocks to
combine forming planets
• This completed the formation of our Solar System
approximately 5 billion years ago
• Evidence Supporting the Big Bang Theory
– Everything is made of the same types of matter and
elements
– Red Shift
Parts and Pieces of the Universe
Universe: Everything! As far as you can see and then
more!
Galaxies: Groups of stars, dust, and gases held together
by gravity. (Gravity is just an attraction between
objects with mass!). We live in the Milky Way galaxy
(100 billion stars!)
Solar System: Planets orbiting a star. Our star is the SUN!
The Universe’s Hierarchy
• The Universe is made of billions of galaxies
• Each galaxy contains approximately 500 billion
stars
• Some stars have planetary systems that rotate
around it (similar to our solar system)
• Each planet functions as a satellite
– A celestial body orbiting a planet or object
• The Earth is a satellite of our Sun
More about gravity…..
Gravity is a force that
- holds us to the Earth
- causes objects to fall to the ground
- causes earth to go around the sun
- causes the Sun to be pulled towards the
center of the Milky Way Galaxy
Gravity acts between any two objects even if
they are far apart!
The Greeks led the way!
600 BC – 150 AD: the Greeks used observations
to develop philosophical arguments to explain
natural events.
Aristotle (350 BC) concluded that the Earth was
round because it always cast a curved shadow
on the moon when it passes between the sun
and the moon.
Greek Models of the Universe
Geocentric Model: At first the Greeks though
that Earth was motionless at the center of the
universe and all planets orbited Earth.
Heliocentric Model: Then they believed that
the Earth and other planets orbited around
the sun.
Ptolemaic System: Later, they were able to
account for the movement of the planets.
Modern Astronomy was born!
• Copernicus (around 1500) concluded that
Earth is a planet just like the other 5 planets
that were known at the time. He proposed a
solar system model with the sun at the center
and the planets orbiting in circles around it.
• Keplar (around 1600) discovered three laws of
planetary motion and determined that the
orbits were elliptical rather than circular.
Kepler’s First Law
• Kepler -showed that planets revolved around
the sun in an ELLIPSE rather than a CIRCLE.
• This is an oval shape that is centered on two foci
points
• The major axis is the line that passes through
both foci
• Each planet has a different orbital size
• Astronomical unit- a planet’s average distance
from the Sun
Kepler’s Second Law
– An imaginary line sweeps out from the
SUN to all of the planets EQUAL amounts
of AREA in equal amounts of time.
• Kepler’s Third Law
– He found a mathematical relationship
between a planet’s ellipse and its orbital
period.
– Kepler’s third law states P 2 = a 3, where P
is a unit of time measured in Earth years,
and a is a unit of length measured in
astronomical units.
Eccentricity
• A planet in elliptical orbit is not at a constant distance
from the Sun
• Perihelion- when a planet is closest to the Sun in its
orbit
• Aphelion- when a planet is furthest away from the Sun
in its orbit
• Eccentricity- the length of the major axis of the elliptical
orbit
• This defines the exact shape of each planet’s orbit
Motion in the Universe
(Reference: www.astrosociety.org)
Think about this…
1. The earth makes one complete rotation in about 24 hours
(1000 miles/hour)
2. The earth makes one complete revolution around the sun
in 1 year (66,000 miles/hour)
3. The sun (and the Earth!) move about toward the bright
star Vega (43,000 miles/hour)
4. AND..the galaxy is spinning! Our sun (and the earth!) take
one galactic year to make it around the Milky Way.
(483,000 miles/hour).
5. Speed limit of the universe: 670,000,000 miles/hour
(aka the speed of light!)
Let’s discuss Earth’s motion..
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Precession
Nutation
Barycenter
Rotation
Revolution
Precession
(wobbling)
A slow motion of Earth’s axis that traces out a cone
over a period of 26,000 years.
Earth’s rotation axis is not fixed! Today, the North
Star is “Polaris”. In 13,000 years, the North Star
will be “Vega.
Precession is mostly caused by the gravitational
influence of the sun and the moon pulling in the
equatorial bulges of the earth
Precession
• Precession is the change in direction of the
axis but not any change in tilt.
• Change of tilt does not affect the seasons.
Nutation
• Nutation- a wobble of the precessional
axis.
• Slight change of 1/2° each way –
• Occurs every 18 year period due to the
gravitational pull of the moon.
– This can increase seasonal affects
Nutation
(a wiggle in the wobble!)
Barycenter
• The common center of mass around which
two or more bodies revolve
• Due to the pull of the planets, the Sun is
not still in the solar system; it rotates
around a center of mass
Earth-Moon Barycenter
• The moon does not orbit the exact center of
the Earth, but a point on a line between the
Earth and the Moon about 1,710 km below
the surface of the Earth. This is where their
masses balance.
The Sun never strays…..
• The Sun never strays too far from the solar
system’s barycenter!
• Remember, the sun is not stationary in our
solar system, but moves as the planets tug on
it (gravity).
Barycenter
Rotation
• Rotation is the turning, or spinning, of a body
on its axis.
• Rotation gives us day and night
Daily Motions
• The sun and moon rise and set everyday due
to the Earth’s Rotation
– The length of a day is the time needed for the
Earth to make one complete turn on its axis
– The time period from sunrise to sunset is called
the solar day
• This also controls our timekeeping system
• Evidence for the Earth’s rotation include
Foucault Pendulums and the Coriolis Effect
Rotation of the Earth Affects Earth’s
Shape
The rotation of the Earth contributes to the shift
of the shape of our planet. It is not a perfect
sphere, but is flattened at the poles and has a
bulge around the equator.
Shape of the Earth
• The Earth is NOT a perfect sphere but an
ellipse.
• The circumference of the Earth is larger
around the equator than around the poles
• There is an equatorial bulge created by the
Earth’s rotation
• A point on the equator is rotating faster than a
point at the poles
• This also causes a lower gravitational pull
towards the equator
– This is why many space stations/ launches are
closer to the equator
Revolution
Earth revolves around the sun in an elliptical
orbit. It takes a year for this to occur.
Since the orbit is elliptical, Earth’s distance from
the sun varies.
Earth is closest to the sun at perihelion.
Earth is farthest from the sun at aphelion.
Annual Motions
• The Earth year is 365.25 days- this is how long it
takes for the Earth to orbit the Sun
• The plane in which the Earth orbits about the Sun
is the ecliptic
– The Earth’s axis is tilted to the ecliptic about 23.5°
• The Earth’s axis stays fixed even as the Earth orbits the Sun
• At different times throughout the year, the Sun
appears to be further away from the Earth.
– This is the Earth’s altitude- the distance from the
observers horizon to the object in the sky
Earth
• The Earth’s distance from the Sun allows
water to exist in all three states of matter
– Solid, liquid, and gas
– This allows for life on the planet
• The Earth’s dense atmosphere and a mild
greenhouse effect makes conditions suitable
for life
The MOON REVOLVES AROUND
EARTH in one MONTH.
Motions of the Moon
• One complete cycle of the moon goes
through all of the phases
– This lasts for 29.5 days ABOUT ONE MONTH.
• Everyday the tide rises and falls due to the
moon’s gravity and orbit
– The effects of the tides can be increased by the
Sun’s gravitational pull
The Effects of Orbits
• There is NOT always a solar eclipse, because the
orbits have to line up in order to block the sun
• The distance between the Sun, Earth, and Moon
changes periodically
– Perigee- the closest point in the Moon’s orbit
to the Earth
– Apogee- the furthest point in the Moon’s orbit
to the Earth