Light and Telescopes

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Light and Telescopes

• Curiosity is one of the permanent and certain
  characteristics of a vigorous mind.
• Samuel Johnson (1709-1784)

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What is Light?

• Dfn.
• Wave- disturbance within a vibrating material
• Water waves (transverse vibration)
• Sound waves (longitudinal vibration
• Demonstrations
• Light wave - consists of rapidly vibrating
  electrical and magnetic disturbances called an
  electromagnetic wave. (Does not require a
  vibrating medium.

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Wave Terms

• Wavelength
• Crest
• Trough

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Wave Frequency

• Number of vibrations per second
• Units of Hz (Hertz) or cycles per second
• Values range from 108 - 1020 vib. per sec.
• Related to wavelength by equation
• c f x l
• c speed of light 3 x 108 m/s
• f frequency in cycles per sec
• l wavelength in meters

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Human Eye Sensitivity
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Speed of light

• 186,000 miles/sec (7 times around the
  circumference of the earth in 1 sec.)
• 3 x 108 m/s or 3 x 105 km/s
• 1 light-year (ly) - the distance light travels in
  one year.
• (3x108 m/s)(365 d/y)(24 h/d)(3600 s/h)
• 9.5 x 1015 m or 6 trillion miles

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Hot Objects emit light

• The bluer the light the hotter the source
• Demo.

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Typical Stars
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Radiation Laws

• Wiens Law
• lmaxT 3x106
• lmax in nm and T is in Kelvin
• Stefan-Boltzman
• Total energy from object is proportional to the
  fourth power of the temperature.
• (If the temperature is doubled the amount of
  energy is (2x2x2x2) times greater (16X)

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Radiation curves for 3 different temperatures.
Thermal Radiation Curves
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Astronomical Observations

• Building Observatories
• Problem of Atmosphere

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Telescope Terms

• Objective- The main lens or mirror that collects
  the light
• Light-gathering power-the ability of a telescope
  to collect light
• Aperture - clear diameter of the lens or mirror.
  Light-gathering power is proportional to the
  square of the aperture.
• Focal length-distance from the lens to the image
  formed of a distance object.
• Eyepiece-the lens that you look through to see
  the image formed by the objective.
• f Number-the ratio of the focal length of the
  objective to the aperture.

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Types of Telescopes-Refractors
Astro-Physics 160 mm f/7.5 8000.00
Orion 60 mm 99.00 700mm, f/11.7
Yerkes Observatory f/19 Worlds largest refractor
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Refractors-How they Work
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Reflectors - Examples
AU observatory 1977 vintage 14 Celstron
f/11 5000.00
Orion 3 reflector f/9.2 99.00
LBT on Mt. Grahmn near Tucson, AZ 500 tons, 2 8.4
m mirrors 120,000,000
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LBT First light 10/12/2005
NGC 891
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Telescope Mounts
alt-azimuth - type of telescope mount, similar to
a camera tripod, that uses a vertical (altitude)
and a horizontal (azimuth) axis to locate an
object.
Typical Alt-azimuth mount
Fork Mount
Dobsonian type mount
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Telescope Mounts
equatorial - type of telescope mount that uses
two axes (right ascension, or polar, and
declination) aligned with the poles to track the
motion of an object across the sky.
New AU German Equatorial Mount
Equatorial Wedge Fork Mount
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AU Telescope
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Types of Reflectors- Cassegrain
Cassegrain
Schmidt Cassegrain
Maksutov-Cassegrain
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Types of Reflectors- Newtonian
Newtonian
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Types of Reflectors- Prime Focus
Prime Focus
Dr. Nicolas Mayall observing at Prime Focus of
the 4 m Mayall Telescope
Kitt Peak National Observatory
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Other Terms

• Image Size
• Proportional to the focal length of the
  telescopes main lens or mirror
• Resolving Power
• The ability to produce sharp, detailed images
  under ideal observing conditions
• Diffraction
• The dispersion of light due to the scattering of
  light due to small imperfections in a surface
• Magnification
• Magnifying power focal length of objective
• focal
  length of eyepiece
• Example AU telescope has focal length of 3900
  mm. What is the magnifying power with a 40 mm
  eyepiece.
• M 3900 mm/ 40mm 97.5

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Maximum Useful Magnification

• The practical limit of useful magnification for
  any telescope is about
• 2X the aperture in mm
• 50X the aperture in inches

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Telescope Aberrations

• Chromatic Aberration
• A lens causes different colors to be bent
  differently, therefore not focusing all colors at
  the same point.
• Achromatic telescopes correct for this with
  multiple lenses.
• Apochromatic telescopes correct with additional
  lenses. Much more expensive.

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Telescope Aberrations

• Spherical Aberration
• Tends to blur a star image and is due to the use
  of a spherical surface instead of a parabolic
  surface.
• The focal point is not the same for all rays
  entering the telescope.

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Telescope Enhancements

• CCD cameras
• Charge coupled detectors greatly enhance the
  sensitivity of the telescope over visual
  observations and photographic film.

The Model ST-7XME is a self-guided imaging camera
and contains two CCD detectors one for guiding
and the other for collecting the image.
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Telescope Enhancements

• Spectrograph
• detects all of the wavelengths of light
• temperature of a hot object composition of an
  object

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Other Eyes on the Universe Radio telescopes
The first radiotelescope and the latest model.
Both are located at the National Radio Astronomy
Observatory. The Robert C. Byrd Green Bank
Telescope (GBT) is 100m by 110 m. It contains
16,000,000 pounds of moving weight.
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Other Eyes on the Universe Infrared Telescope
The Spitzer Space Telescope (formerly SIRTF, the
Space Infrared Telescope Facility) was launched
into space by a Delta rocket from Cape Canaveral,
Florida on 25 August 2003. During its 2.5-year
mission, Spitzer will obtain images and spectra
by detecting the infrared energy, or heat,
radiated by objects in space .
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Other Eyes on the Universe Hubble Space
Telescope
Hubble Site
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Other Eyes on the Universe Gamma Ray Telescope
GLAST is a next generation high-energy gamma-ray
observatory designed for making observations of
celestial gamma-ray sources in the energy band
extending from 10 MeV to more than 100 GeV. The
projected launch date for GLAST is the fall of
2007.
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Other Eyes on the Universe X-Ray
TelescopeChandra
Since its launch on July 23, 1999, the Chandra
X-ray Observatory has been NASA's flagship
mission for X-ray astronomy.