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• Solar System Consists of the Sun, and everything
  bound to it by gravity. This includes the 8
  planets and their moons, the asteroids, the dwarf
  planets, all the Kuiper belt objects, the
  meteoroids, comets and interplanetary dust.
• Galaxy large system of stars held together by
  mutual gravitation and isolated from similar
  systems by vast regions of space. The Milky Way
  measures about 100,000 light-years across, and is
  thought to contain 200 billion stars.
• Universe the totality of known or supposed
  objects and phenomena throughout space the
  cosmos macrocosm

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Origin of Modern Astronomy
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Early Astronomy
? Astronomy is the science that studies the
universe. It includes the observation and
interpretation of celestial bodies and phenomena.
? The Greeks used philosophical arguments to
explain natural phenomena.
? The Greeks also used some observational data.
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Early Astronomy
? Geocentric Model Ptolemy Greek Astronomer
In the ancient Greeks geocentric model, the
moon, sun, and the known planetsMercury, Venus,
Mars, and Jupiterorbit Earth.
? Heliocentric Model Nicolaus Copernicus
In the heliocentric model, Earth and the other
planets orbit the sun.
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Early Astronomy
? Nicolaus Copernicus
Copernicus concluded that Earth is a planet.
He proposed a model of the solar system with the
sun at the center. Heliocentric Model This
model explained the retrograde motion of planets
better than the geocentric model.
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Early Astronomy
? Tycho Brahe
Tycho Brahe designed and built instruments to
measure the locations of the heavenly bodies.
Brahes observations, especially of Mars, were
far more precise than any made previously.
? Johannes Kepler

• Kepler discovered three laws of planetary
  motion
• 1. Orbits of the planets are elliptical.
• 2. Planets revolve around the sun at varying
  speed.
• 3. There is a proportional relationship between a
  planets orbital period and its distance to the
  sun.

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Early Astronomy
German astronomer Johannes Kepler (1571-1630)
helped establish the era of modern astronomy by
deriving three laws of planetary motion.
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Early Astronomy
? Galileo Galilei
Italian scientist Galileo Galilei (15641642)
used a new invention, the telescope, to observe
the Sun, Moon, and planets in more detail than
ever before.
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Early Astronomy
? Sir Isaac Newton
English scientist Sir Isaac Newton (16421727)
explained gravity as the force that holds planets
in orbit around the Sun.
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Gravitys Influence on Orbits
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Newtons Laws of Motion

• 1st Law
• A body at rest, or in uniform motion, will remain
  so unless acted upon by an unbalanced force.
• 2nd Law
• The change in motion (acceleration) is
  proportional to the unbalanced force
• 3rd Law
• For every action there is an equal and opposite
  reaction

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Gravity

• Gravity is the force that
• holds us to the Earth
• causes a rock to fall towards the ground
• causes the 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.
• action at a distance

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Summary

• Keplers and Galileos Laws provided Newton with
  important clues that helped him formulate his
  laws of motion
• Newton arrived at 3 laws that govern the motion
  of objects
• The law of inertia
• The law of force
• The law of action and reaction
• Newton also arrived at a law of gravity
• But it seemed to require action at a distance!

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Earth Science
Light and Astronomical Observations
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Important Astronomical Measurements
An ellipse is an oval-shaped path.
An astronomical unit (AU) is the average distance
between Earth and the sun it is about 150
million kilometers.
Light-year The distance that light travels in one
year, about 9.5 trillion kilometers.
Parsec A unit of measurement used to describe
distances between celestial objects, equal to
3.258 light-years.
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The study of light

• Electromagnetic radiation
• Visible light is only one small part of an array
  of energy
• Electromagnetic radiation includes
• Gamma rays
• X-rays
• Ultraviolet light
• Visible light
• Infrared light
• Radio waves

Energy radiated in the form of a wave, resulting
from the motion of electric charges and the
magnetic fields they produce.
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The study of light

• Electromagnetic radiation
• All forms of radiation travel at 300,000
  kilometers (186,000 miles) per second

• Light (electromagnetic radiation) can be
  described in two ways
• Wave model
• Wavelengths of radiation vary
• Radio waves measure up to several kilometers long
• Gamma ray waves are less than a billionth of a
  centimeter long
• White light consists of several wavelengths
  corresponding to the colors of the rainbow

A continuum depicting the range of
electromagnetic radiation, with the longest
wavelength at one end and the shortest at the
other.
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• Light (electromagnetic radiation) can be
  described in two ways
• Particle model
• Particles called photons
• Exert a pressure, called radiation pressure, on
  matter
• Shorter wavelengths correspond to more energetic
  photons

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The study of light

• Spectroscopy
• The study of the properties of light that depend
  on wavelength
• The light pattern produced by passing light
  through a prism, which spreads out the various
  wavelengths, is called a spectrum (plural
  spectra)

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The study of light
A spectrum is produced when white light passes
through a prism
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The Doppler effect
Originally discovered by the Austrian
mathematician and physicist, Christian Doppler
(1803-53), this change in pitch results from a
shift in the frequency of the sound waves.
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The Doppler effect
The electromagnetic radiation emitted by a moving
object also exhibits the Doppler effect.

• Redshift, a phenomenon of electromagnetic waves
  such as light in which spectral lines are shifted
  to the red end of the spectrum.

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The Doppler effect
The radiation emitted by an object moving toward
an observer is squeezed its frequency appears to
increase and is therefore said to be blueshifted.
In contrast, the radiation emitted by an object
moving away is stretched or redshifted.
Blueshifts and redshifts exhibited by stars,
galaxies and gas clouds also indicate their
motions with respect to the observer.
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The Big Bang Theory
The theory holding that the universe originated
from the instant expansion of an extremely small
agglomeration of matter of extremely high density
and temperature.
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Photons converted into particle-antiparticle
pairs and vice-versa E mc2 Early universe
was full of particles and radiation because of
its high temperature
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The Big Band Theory

• Evidence for Big Bang

• This is the theory of the universes earliest
  moments.
• It presumes that the universe began from a tiny,
  hot, and dense collection of matter and
  radiation.
• It describes how expansion and cooling of
  particles could have led to the present universe
  of stars and galaxies.
• It explains several aspects of todays universe
  with a very good accuracy.

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Evidence for the Big Bang
In 1927, the Belgian priest Georges Lemaître was
the first to propose that the universe began with
the explosion of a primeval atom.