Optics Basics

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Optics Basics
All telescopes are based upon two basics
properties of optics Mirror An object which is
not transparent to EM waves Lens An object
which is transparent to EM waves. Reflection
The bouncing of light of surfaces - mirrors
Refraction The bending of light through
transparent materials - lenses
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Optics Basics - Reflection
The angle of incidence TI is equal to the angle
of reflection Tr
Ti
Tr
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Optics Basics - Reflection
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Optics Basics - Reflection
Focal Length
Focal Length (f) identifies the distance from the
mirror where an image of the object will form if
the object is very far away.
Image
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Optics Basics Refraction
An electromagnetic wave traveling through a
transparent material (not a vacuum) travels at a
speed less than 3 x 108 m/sec The amount of
slowing is characterized by the index of
refraction of the material, n.
c
n
Speed in the material
The larger the index of refraction, the slower
the em wave travels
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Optics Basics Refraction
Ti
Tr
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Optics Basics Refraction
Ti
Tr
The bending of the light ray due to the change in
speed of the light is called refraction.
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Optics Basics Refraction
Image
Focal Length
Focal Length (f) identifies the distance from the
lens where an image of the object will form if
the object is very far away.
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Optics Basics Light Gathering
The large mirror or lens that is the primary
collector of EM energy is called the objective
mirror or objective lens. The number of photons
collected by the telescope is directly
proportional to the area of the objective. Since
the area of the objective is proportional to the
diameter of the objective squared, Number of
photons collected is proportional to d2 Finally,
the brightness of the image is proportional to
the number of photons collected, Image
brightness is proportional to d2
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Optics Basics Refraction
Image
Eyepiece
A short focal length lens, called an eyepiece, is
used as a simple magnifier to examine the image.
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Refractors
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Refractors
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Reflectors
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Newtonian Reflectors
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Catadioptric Reflectors Also Known as Compound
Telescopes
Compound telescopes fold the path of the light
back upon itself. The result is a short barrel
telescope that is very convenient for amateur
astronomers because of the telescopes
transportability. The two most popular designs
of catadioptric telescopes are Schmidt-Cassegrain
and Maksutov-Cassegrain. They each use
differently shaped lenses and mirrors to achieve
a similar quality aperture in an easy-to-carry
size. For people who like to take their telescope
to a remote location and track distant objects
across the night sky, a compound telescope is a
great fit.
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Catadioptric Reflectors Schmidt Cassegrain
Telescope
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Catadioptric Reflectors Maksutov Cassegrain
Telescope
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Cheap Telescope design the Dobsonian
Telescope Newtonian Reflector
See the links in the PHY250 website for building
instructions
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Other Applications
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Radio Telescope
National Radio Astronomical Observatory at Green
Bank, Va.
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Radio Telescope
National Radio Astronomical Observatory at Green
Bank, Va.
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Radio Telescope
Radio Wave Emission from the Center of the Milky
Way
Radio Continuum (408 MHz) Intensity of radio
continuum emission from high-energy charged
particles in the Milky Way,from surveys with
ground-based radio telescopes (Jodrell Bank Mark
I and Mark IA, Bonn 100-meter, and Parkes
64-meter). At this frequency, most of the
emission is from electrons moving through the
interstellar magnetic field at nearly the speed
of light. Shock waves from supernova explosions
accelerate electrons to such high speeds,
producing especially intense radiation near these
sources. Emission from the supernova remnant Cas
A near 110 longitude is so intense that the
diffraction pattern of the support legs for the
radio receiver on the telescope is visible as a
cross shape. Frequency 408 MHz Angular
resolution 51 arcminutes
Jodrell Bank Lowell Telescope
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Infrared Telescope
Infrared Emission from the Center of the Milky Way
Infrared Composite mid-and far-infrared
intensity observed by the Infrared Astronomical
Satellite (IRAS) in 12, 60, and 100 micron
wavelength bands. The images are encoded in the
blue, green, and red color ranges, respectively.
Most of the emission is thermal, from
interstellar dust warmed by absorbed starlight,
including star-forming regions embedded in
interstellar clouds. The display here is a mosaic
of IRAS Sky Survey Atlas images. Emission from
interplanetary dust in the solar system, the
"zodiacal emission," was modeled and subtracted
in the production of the Atlas. Frequencies 3.0
x 103-25 x 103 GHz Angular resolution 5
arcminutes
Infrared Astronomical Satellite
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Orion Optical Wavelength Image
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Infrared Telescope
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Infrared Telescope
Stars bright in different lightThis infrared
portrait of the Orion starbirth region was taken
by the European Southern Observatorys new VISTA
telescope, the worlds largest wide-field-of view
telescope. The image, which measures about 35
light-years from top to bottom, records radiation
with about twice the wavelength of light visible
to the human eye. Many of the red features just
above the center are young stars and the
high-speed streams of gas they eject. These stars
are completely hidden by dust in visible light
but can be seen at dust-penetrating infrared
wavelengths. Feb 10, 2010
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Optical Telescopes
Visible Emission from the Center of the Milky Way
Optical Intensity of visible (0.4 - 0.6 micron)
light from a photographic survey. Due to the
strong obscuring effect of interstellar dust,the
light is primarily from stars within a few
thousand light-years of the Sun, nearby on the
scale of the Milky Way. The widespread bright red
regions are produced by glowing, low-density gas.
Dark patches are due to absorbing clouds of gas
and dust, which are evident in the Molecular
hydrogen and Infrared maps as emission regions.
Stars differ from one another in color, as well
as mass, size and luminosity. Interstellar dust
scatters blue light preferentially, reddening the
starlight somewhat relative to its true color and
producing a diffuse bluish glow. This scattering,
as well as absorption of some of the light by
dust, also leaves the light diminished in
brightness. The panorama was assembled from
sixteen wide-angle photographs taken by Dr. Axel
Mellinger using a standard 35-mm camera and color
negative film. The exposures were made between
July 1997 and January 1999 at sites in the United
States, South Africa, and Germany. Frequency
460 x 103 GHz Angular resolution 1 arcminute
Hubble Space Telescope (HST)
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Ultraviolet Telescopes
Ultraviolet You might notice that missing from
the list of images is the ultraviolet region of
the electromagnetic (EM) spectrum. Ultraviolet
radiation begins just past the blue/violet region
of the visible (optical) spectrum, and ends when
X-rays take over. The boundaries between named
regions can get a little blurred, especially if
the broad-band regions (example infrared) are
further broken into sub-regions (example near
infrared and far infrared). One reference on EM
waves says microwaves extend from about 1
millimeter to about 10 centimeters. In that case,
the map of molecular hydrogen would fall into the
category of microwaves. The sky has been observed
at ultraviolet wavelengths with various detectors
links to EUVE, IUE, etc. will be listed. An
all-sky image has not been presented here because
it is relatively featureless. You may view an
all-sky survey map in the extreme-ultra-violet at
http//archive.stsci.edu/euve/images/jbis_map.gif.
The image at that site comes from data obtained
with the Extreme Ultraviolet Explorer (EUVE).
Extreme Ultraviolet Explorer
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X-ray Telescopes
X-Ray Emission from the Center of the Milky Way
X-Ray Composite X-ray intensity observed by the
Position-Sensitive Proportional Counter (PSPC)
instrument on the Röntgen Satellite (ROSAT).
Images in three broad, soft X-ray bands centered
at 0.25 , 0.75, and 1.5 keV are encoded in the
red, green, and blue color ranges, respectively.
In the Milky Way, extended soft X-ray emission is
detected from hot, shocked gas. At the lower
energies especially, the interstellar medium
strongly absorbs X-rays, and cold clouds of
interstellar gas are seen as shadows against
background X-ray emission. Color variations
indicate variations of absorption or of the
temperatures of the emitting regions. The black
regions indicate gaps in the ROSAT survey.
Frequency 60-360 x 106 GHz Angular
resolution 115 arcminutes
ROSAT
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Gamma Ray Telescopes
Gamma Ray Emission from the Center of the Milky
Way
Gamma Ray Intensity of high-energy gamma-ray
emission observed by the Energetic Gamma-Ray
Experiment Telescope (EGRET) instrument on the
Compton Gamma-Ray Observatory (CGRO). The image
includes all photons with energies greater than
300 MeV. At these extreme energies, most of the
celestial gamma rays originate in collisions of
cosmic rays with hydrogen nuclei in interstellar
clouds. The bright, compact sources near Galactic
longitudes 185, 195, and 265 indicate
high-energy phenomena associated with the Crab,
Geminga, and Vela pulsars, respectively.
Frequencies gt2.4 x 1013 GHz Angular
resolution 120 arcminutes
CGRO
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Milky Way Object Finder
Finder Diagram Major structural features of the
Milky Way (red), optical H II regions (blue),
radio sources (green), and OB associations
(purple) are labeled in the finder chart. The
image in the finder chart is derived from the
IRAS 100 micron map of intensity with contours
from the COBE DIRBE 3.5 micron map overlaid. The
axes of the finder diagram are labeled in degrees
of Galactic longitude and latitude.
Then mosaics in the previous transparencies were
taken from the website of the Astrophysics Data
Facility (ADF) at the NASA Goddard Space Flight
Center (GSFC).