VIEWS OF OUR UNIVERSE UNIT: Electromagnetic Spectrum/Waves Notes

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VIEWS OF OUR UNIVERSE UNIT Electromagnetic
Spectrum/Waves Notes

• Astronomy

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• Wave a rhythmic disturbance that carries energy
  through matter or space

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Types of Waves

• Transverse Wave - a wave that vibrates
  perpendicular to the direction of the waves
  motion
• Longitudinal Wave - a wave that vibrates parallel
  to the direction of the waves motion

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Characteristics of Waves

• Crest - the high points of a wave
• Trough - the low points of a wave
• Amplitude(A) - the distance from the midpoint of
  a wave to its crest or trough

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More Characteristics of Waves

• Wavelength (?) - the distance between two
  consecutive points on a wave (ex crest to crest)
• Frequency (f) - the number of waves that pass a
  given point in one second, measured in Hertz(Hz)

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More Characteristics of Waves

• Rarefaction - part of a longitudinal wave where
  the molecules are spread farther apart
• Compression - part of a longitudinal wave where
  the molecules are closer together

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• Speed of a wave vf ? (velocity
  frequencyXwavelength)
• Interference of waves - when two or more waves
  combine they combine to form a new wave

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Types of Interference

• Constructive Interference - when two or more
  waves combine to make a bigger wave than the
  original ones
• Destructive Interference - when two or more waves
  combine to make a smaller wave than the original
  ones

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Constructive Interference
Destructive Interference
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• Sound - longitudinal waves produced by the
  vibration of objects, the speed of sound depends
  on the elasticity of the medium it travels
  through and the temperature of the medium it
  travels through

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• Sound (again) - speed of sound in room
  temperature air is 340 m/s, sound travels faster
  in liquids than in gases and faster in solids
  than in liquids

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• Light
• an electromagnetic transverse wave
• it travels in a straight line at 3X108 m/s in
  space
• each type of light has a different wavelength
  with gamma rays the shortest wavelength and radio
  waves the longest

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There are seven types of light (in order from the
longest wavelength to the shortest)Radio Waves,
Microwaves, Infrared Waves, Visible Light (red,
orange, yellow, green, blue, indigo, violet),
Ultraviolet Light, X-Rays, Gamma Rays
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• Visible Spectrum - the part of light we can see
  made of seven colors ROY G BIV (red, orange,
  yellow, green, blue, indigo, violet)
• White - the reflection of all colors together
• Black - absorption of all colors together

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• Primary Colors of Light - red, green, blue (when
  you mix these you get white light)
• Primary Colors of Pigments(things that absorb
  certain colors and transmit others) - yellow,
  cyan, magenta (when you mix these colors you get
  black)

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• Polarization - when light can only travel/vibrate
  in one direction
• Refraction - the bending of waves as they go from
  one medium to another
• Diffraction - the bending of waves around objects

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• Reflection - when waves bounce back off an object

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• Law of Reflection - the angle of incidence equals
  the angle of reflection
• Lenses - refract light
• Mirrors - reflect light
• Prisms - separate light into the visible spectrum
  by refraction

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• Types of Objects
• a)opaque - no light gets through
• b)translucent - some light gets through but no
  image
• c)transparent - all light gets through so an
  image is seen

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How Objects Produce Light

• An electron has a natural orbit that it occupies,
  but if you energize an atom you can move its
  electrons to higher orbitals.

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• A photon of light is produced whenever an
  electron in a higher-than-normal orbit falls back
  to its normal orbit.

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• During the fall from high-energy to
  normal-energy, the electron emits a photon -- a
  packet of energy -- with very specific
  characteristics. The photon has a frequency, or
  color, that exactly matches the distance the
  electron falls.

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How We See Objects in Light Other Than Visible

• Telescopes are connected to computers that take
  the light they receive, calculate the amount of
  light coming from a specific area, and translate
  that light intensity into color. The computers
  then generate pictures we can see using the
  information the telescopes provided on the light
  intensity.

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Radio Astronomy

• Radio waves are given off by many astronomical
  objects. They are very long waves that can
  penetrate gas and dust clouds in space allowing
  us to see behind nebula we would not be able to
  with visible light. Radio waves also penetrate
  into our atmosphere with little interference.
  Two of the most well-known radio telescopes are
  the VLA and Arecibo.

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Cassiopeia A supernova remnant in radio light
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Triangulum Galaxy in radio and visible light
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Microwave Astronomy

• Microwaves are produced by many objects in space.
  They do not penetrate into our atmosphere easily
  though. We must put probes and satellites into
  space to observe the microwaves produced by
  celestial objects. Microwave astronomy is mostly
  used to study the microwave radiation given off
  at the Big Bang called cosmic microwave
  background radiation.

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Cosmic Microwave Background Radiation taken by
WMAP
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Infrared Astronomy

• Infrared Astronomy is the detection and study of
  the infrared radiation (heat energy) emitted from
  objects in the Universe. All objects emit
  infrared radiation. Only since the early 1980's
  have we been able to send infrared telescopes
  into orbit around the Earth, above the atmosphere
  which hides most of the Universe's light from us.
  The first of these satellites - IRAS (Infrared
  Astronomical Satellite) - detected about 350,000
  infrared sources, increasing the number of
  cataloged astronomical sources by about 70.

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All Sky Map of IRAS Point Sources The plane of
our galaxy runs horizontally across the image.
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• In space, there are many regions which are hidden
  from optical telescopes because they are embedded
  in dense regions of gas and dust. However,
  infrared radiation, having wavelengths which are
  much longer than visible light, can pass through
  dusty regions of space without being scattered.
  This means that we can study objects hidden by
  gas and dust in the infrared, which we cannot see
  in visible light, such as the center of our
  galaxy and regions of newly forming stars.

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• The center of our galaxy in red light (at top),
  near-infrared light (middle) and far-infrared
  (bottom). Notice the different information
  gathered in each light.

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Visible Light Astronomy

• Visible astronomy, also called optical astronomy,
  encompasses all the information gathered from
  space that can be seen by our eyes. Until a
  couple of decades ago, all information gathered
  from space was in the visible spectrum. We can
  use both Earth-based and space-based telescopes
  to gather visible information. Because visible
  light will not readily pass through objects,
  nebulae can block our view of the visible light
  emitted by objects in space. The most famous
  optical telescope in the world is the Hubble
  Space Telescope.

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Galaxy M100 taken by HST
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Center of Galaxy Centaurus A taken by HST
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Galaxy Triplet Arp 274 taken by HST
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Star Clusters in the Large Magellanic Cloud taken
by HST
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Quadruple Moon Transit of Saturn taken by HST
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A Cosmic String of Pearls surrounds an
exploding star taken by HST
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Ultraviolet Astronomy

• Because Earths atmosphere absorbs so much UV
  radiation, much of UV astronomy is now done from
  space and sometimes from rockets and balloons.
  Planets, stars and galaxies all produce UV
  radiation. It is UV radiation that helps us
  absorb vitamin D, gives us suntans, can give us
  sunburns, and can cause skin cancer.

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X-Ray Astronomy

• Earths atmosphere absorbs most of the incoming
  x-rays from space so X-ray telescopes need to be
  space-based. X-rays are given off by stars
  (especially neutron stars) and also by the light
  that gets absorbed into black holes. The Chandra
  X-ray Observatory is the most famous x-ray
  telescope in use today.

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Gamma Ray Astronomy

• Gamma rays are absorbed by Earths atmosphere so
  Gamma ray telescopes are space-based. Processes
  that produce gamma rays include cosmic ray
  interactions with interstellar gas, supernova
  explosions, and interactions of energetic
  electrons with magnetic fields.

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• Gamma-ray bursts are short-lived bursts of
  gamma-ray photons, the most energetic form of
  light. At least some of them are associated with
  a special type of supernovae, the explosions
  marking the deaths of especially massive stars.
• Lasting anywhere from a few milliseconds to
  several minutes, gamma-ray bursts (GRBs) shine
  hundreds of times brighter than a typical
  supernova and about a million trillion times as
  bright as the Sun, making them briefly the
  brightest source of cosmic gamma-ray photons in
  the observable Universe. GRBs are detected
  roughly once per day from wholly random
  directions of the sky.

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