Astronomy Unit 2

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Astronomy Unit 2

• Telescopes
• Celestial Spheres/Constellations
• Apparent Motion of the Stars
• Motion of the Planets

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Telescopes

• Vocab Words for this section are
• Reflecting Telescope
• Refracting Telescope
• Radio Telescope
• Space Telescope

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Telescopes

• Hans Lippershey was the inventor of the telescope
  in 1608.
• Galileo was the first to use a telescope to study
  the sky in 1609.
• The invention and use of the telescope began a
  huge number of discoveries in the field of
  astronomy.

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Telescopes

• 3 types of telescopes
• Optical Telescopes study visible light.
• Reflecting telescopes use mirrors to bounce light
  from an objective lens to an eyepiece lens
• Refracting telescopes use lens to bend light and
  magnify images coming through an objective lens.
• Radio Telescopes study radio waves from earth.
• Space Telescopes travel out of Earths atmosphere
  to study the other types of radiation not visible
  to the naked eye, and the radiation that cannot
  make it through earths protective atmosphere.

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Telescopes

• Optical Telescopes study the visible light
  section of the electromagnetic spectrum.
• They uses mirrors and/or lenses to magnify the
  light.

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Telescopes

• One type of Optical Telescope is the Reflecting
  Telescope
• Within this telescope there are mirrors to bounce
  the light traveling through.

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Telescopes

• Another type of Optical telescopes is the
  Refracting Telescope
• Within this telescope there are lenses to bend
  the light traveling through.

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Telescopes

• Radio Telescopes use a parabolic antenna and a
  receiver to study radio waves.
• Radio Waves are a type of radiation that is not
  normally visible to the naked eye.

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Telescopes

• Space telescopes travel out of earths atmosphere
  to study all different types of radiation that
  can not make it through earths atmosphere.
• Examples are the Hubble Space Telescope and the
  Chandra Space Telescopes

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Celestial Sphere/Constellations

• Vocab words for this section are
• Celestial Sphere
• Declination
• Right Ascension
• Constellation
• Circumpolar Constellation
• North Circumpolar Constellation
• South Circumpolar Constellation
• Zodiac
• Ecliptic

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Celestial Sphere/Constellations

• A celestial sphere is similar to a globe of the
  sky.
• It is an imaginary sphere where the sun, the
  moon, and all the other stars appear to be
  combined.

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Celestial Sphere/Constellations

• To locate on the celestial sphere, you use
  declination and right ascension.
• Declination measures angular distance North or
  South of the celestial equator
• Between 0 and 90 degrees
• Right Ascension measures distances eastward,
  along the celestial equator from the vernal
  equinox
• Goes up to 360 degrees

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Celestial Sphere/Constellations

• The 88 recognized constellations by the
  International Astronomical Union are plotted on
  the Celestial Sphere.
• Some constellations are close enough to a
  celestial pole that they are visible in certain
  locations on earth all year long. These
  constellations are called Circumpolar
  Constellations.

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Celestial Sphere/Constellations

• Constellations close to the N. Celestial Pole are
  North Circumpolar Constellations
• They are visible from the North Pole all year
  long!
• Constellations close to the S. Celestial Pole are
  South Circumpolar Constellations.
• They are visible from the South Pole all year
  long!

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Celestial Sphere/Constellations

• These are the North Circumpolar Constellations

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Celestial Sphere/Constellations

• These are the South Circumpolar Constellations

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Celestial Sphere/Constellations

• The ecliptic is the apparent path the sun traces
  out in the sky throughout the year.
• It is visible on the celestial sphere!
• Along the ecliptic there is a band of 12
  constellations. They are called the zodiac
  constellations
• These are where astrological signs come from.
  The constellation that rises and sets during the
  month of your birthday is supposedly your sign.

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Celestial Sphere/Constellations

• The 12 constellations of the zodiac are

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Apparent Motion of the Stars

• Vocab Words for this section are
• Constellation
• Circumpolar Constellation
• Diurnal Circles
• Parallax

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Apparent Motion of the Stars

• We have previously discussed circumpolar
  constellations.
• This concept deals with how stars appear to move
  throughout the year.

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Apparent Motion of the Stars

• If you trace the path a star makes each day, it
  would trace out a Diurnal Circle.
• This the circular path a star appears to take
  each day.
• We cant see stars during the daytime because of
  the sun, so we dont actually see the circle.

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Apparent Motion of the Stars

• Diurnal Circles

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Apparent Motion of the Stars

• Stars also display parallax.
• Parallax is the apparent movement of an object
  due a change in the viewers position.
• You can try it with your finger.
• Hold your finger in front of your face. Close
  your left and view your finger from your right
  eye. Quickly switch eyes. Go back and forth a
  few times. Your finger should appear to move
  even though it isnt actually moving.
• As the earth moves around the sun, it changes our
  viewing position of stars. This causes them to
  display parallax!

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Apparent Motion of the Stars

• We use a stars parallax (or apparent shift)
  relative to fixed background stars, to
  determine the distance to stars.
• Stars that are further away display less of a
  parallax, than stars that are close to us.

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Motion of the Planets

• Vocab Words for this section are
• Sidereal Motion
• Prograde
• Retrograde
• Keplers 1st Law of Planetary Motion
• Keplers 2nd Law of Planetary Motion
• Ellipse

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Motion of the Planets

• A sidereal day actually takes 23 hours, 56
  minutes and 4.09 seconds
• This is the amount of time it takes the earth to
  get back to the same location it was at
  previously.
• We dont use this as a day because the earth not
  only rotates, but it moves a little bit around
  the sun in its revolution during each rotation.
  This is where we get the 24 hour day from.

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Motion of the Planets

• As we watch planets move across the sky, they
  move relative to their background fixed stars.
• Planets normally move westward across the night
  sky. This is called Prograde motion.
• Sometimes planets appear to begin moving
  backward or eastward across the night sky.
  This is called Retrograde motion.
• Please not that if you look these words up, the
  directions will be backwards because Astronomers
  pretend like you are living on the planet looking
  out. For our purposes we define the word as how
  it looks in the night sky!

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Motion of the Planets

• The planets dont actually switch directions.
• What is happening is our orbits around the sun
  (the earths and whichever planet we are looking
  at) are catching up with each other.
• This makes the planet appear to move backwards
  for a small portion of time.
• See the animation at the following website to
  help you understand prograde vs. retrograde
  motion
• Prograde vs. Retrograde Motion

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Motion of the Planets

• Johannes Kepler developed 3 laws for how the
  planets move around the sun. He did this after
  making detailed studies and observations as to
  how the planets are moving.
• We are going to study the first 2!
• These laws dont only apply to planets, but they
  also apply to how moons orbit their parent
  planets!

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Motion of the Planets
Keplers First Law of Planetary Motion
Planets follow elliptical orbits, with the Sun at
one focus of the ellipse.
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Motion of the Planets

• The planets move around the sun in an elliptical
  shape with the sun at one of the foci.
• An ellipse appears as a squashed circle.
• It is defined as a closed loop where the sum of
  the distances from 2 points (the foci) to every
  point on the line is constant.

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Motion of the Planets

• This means there are times throughout the year
  where the earth is closer and further from the
  sun.
• The earth is actually closer to the sun in
  December, our winter!
• It is about 147,450,000 km from the sun
• The earth is further from the sun in June, our
  summer!
• It is about 152,400,000 km from the sun

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Motion of the Planets
Keplers 2nd Law of Planetary Motion
As a planet moves in its orbit, it sweeps out an
equal amount of area in an equal amount of time.
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Motion of the Planets

• Keplers 2nd Law implies that when a satellite is
  closer to its parent object, it actually travels
  faster than when it is further away!
• When we are closer to the sun we travel slightly
  faster than when we are further away.
• This is due to the gravitational pull the parent
  object has on the satellite.
• The pull the sun has on the earth
• On average the earth travels at 29.78 km/s

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Motion of the Planets

• Keplers Laws apply to ALL the planets that orbit
  the sun.
• Keplers Laws also apply to how every moon orbits
  its parent planet!