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Telescopes

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How do they work? History Hans Lippershey Middleburg, Holland invented the refractor telescope in 1608 Galileo the first to use a telescope in astronomy. – PowerPoint PPT presentation

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Title: Telescopes


1
Telescopes
  • How do they work?

2
1. History
2. Lenses Hardware
3. Reflecting Telescopes
4. Refracting Telescopes
3
History
  • Hans Lippershey Middleburg, Holland
  • invented the refractor telescope in 1608
  • Galileo
  • the first to use a telescope in astronomy.
    Galileo's designs used a combination of convex
    and concave lenses.
  • Kepler
  • improved the design to have two convex lenses,
    which made the image upside-down. Kepler's design
    is still the major design of refractors today,
    with a few later improvements in the lenses and
    the glass to make them.

4
Why cant you see an object that is far away?
  • The answer is simple the object does not take up
    much space on your eyes screen (retina).
  • Using a digital camera analogy, at 150 feet the
    writing on a dime does not cover enough pixels on
    your retinal sensor for you to read the writing.
  • This can be corrected by bending the light with
    lenses.

5
Lenses
  • The lens in your eyes works like a glass lens.
    The light bends as it goes through a different
    medium.
  • Light rays are bent when they intersect glass a
    curved surface can produce an image.
  • In your eye, the image is then focused at the
    retina.

6
How does this apply to telescopes?
  • If you had a bigger eye, you could collect more
    light from the object. This image could be
    magnified so it stretches out over more pixels in
    your retina.
  • In a telescope, two pieces make this possible
  • the objective lens (refractor telescopes) or
    primary mirror (reflecting telescopes)
  • the eye piece

7
  • The objective lens (in refractors) or primary
    mirror (in reflectors) collects lots of light
    from a distant object and brings that light, or
    image, to a point or focus.
  • An eyepiece lens takes the bright light from the
    focus of the objective lens or primary mirror and
    "spreads it out" (magnifies it) to take up a
    large portion of the retina. This is the same
    principle that a magnifying glass (lens) uses it
    takes a small image on the paper and spreads it
    out over the retina of your eye so that it looks
    big.

8

Diagram of a simple telescope. Parallel light rays enter from the left, pass through the objective lens, come to a focus at the focal plane, and exit through the eyepiece lens. The focal length of the objective is F, and the focal length of the eyepiece is f. www.ifa.hawaii.edu
9
  • When you combine the objective lens or primary
    mirror with the eyepiece, you have a telescope.
  • Again, the basic idea is to collect lots of light
    to form a bright image inside the telescope, and
    then use something like a magnifying glass to
    magnify (enlarge) that bright image so that it
    takes up a lot of space on your retina.

10
A telescope has two general properties
  • how well it can collect the light
  • (the aperature)
  • how much it can magnify the image
  • (the magnification)

11
The Aperture
  • A telescope's ability to collect light is
    directly related to the diameter of the lens or
    mirror -- the aperture -- that is used to gather
    light. Generally, the larger the aperture, the
    more light the telescope collects and brings to
    focus, and the brighter the final image.

12
Magnification
  • The telescope's magnification, its ability to
    enlarge an image, depends on the combination of
    lenses used. The eyepiece performs the
    magnification. Since any magnification can be
    achieved by almost any telescope by using
    different eyepieces, aperture is a more important
    feature than magnification

13
A closer look at eyepieces
                                                                                                                        View through an eyepiece. Note that the image is upside-down.
14
Eyepiece
  • The purposes of the eyepiece are to
  • produce and allow you to change the telescope's
    magnification
  • produce a sharp image
  • provide comfortable eye relief (the distance
    between your eye and the eyepiece when the image
    is in focus)
  • determine the telescope's field of view
  • apparent - how much of the sky, in degrees, is
    seen edge-to-edge through the eyepiece alone
    (specified on the eyepiece)
  • true or real - how much of the sky can be seen
    when that eyepiece is placed in the telescope
    (true field apparent field/magnification)

15
Filters
  • Filters are pieces of glass or plastic that you
    can place in the barrel of an eyepiece to
    restrict the wavelengths of light that come
    through in the image.
  • Set of filters for viewing, including a light
    pollution filter (left) and colored filters for
    enhancing contrast in planetary images.
  • Filters can be used to
  • enhance the viewing of faint sky objects in
    light-polluted skies
  • enhance the contrast of fine features and details
    on the moon and planets
  • safely view the sun

16
There are 2 main types of Telescopes
  • Refractor telescopes, which use glass lenses
  • Reflector telescopes, which use mirrors instead
    of lenses.
  • Both types accomplish exactly the same thing, but
    in completely different ways.

17
Refractor Telescopes
  • Refractors are the type of telescope that most of
    us are familiar with. They have the following
    parts
  • a long tube, made of metal, plastic, or wood
  • a glass combination lens at the front end
    (objective lens)
  • a second glass combination lens (eyepiece)
  • Refracting telescopes focus light rays by bending
    them with glass.

18
                                                                                                                                                                                                                                                
This is the simplest telescope design you could
have. A big lens gathers the light and directs it
to a focal point and a small lens brings the
image to your eye.
19
Refracting telescopes are not used for
astronomical research (anymore) because they are
large and have heavy lenses (i.e. expensive).
20
Reflecting Telescopes
  • History
  • Isaac Newton developed the reflector about 1680,
    in response to the chromatic aberration (rainbow
    halo) problem that plagued refractors during his
    time. Instead of using a lens to gather light,
    Newton used a curved, metal mirror (primary
    mirror) to collect the light and reflect it to a
    focus. Because the mirror reflected light back
    into the tube, he had to use a small, flat mirror
    (secondary mirror) in the focal path of the
    primary mirror to deflect the image out through
    the side of the tube, to the eyepiece otherwise,
    his head would get in the way of incoming light.
  • In 1722, John Hadley developed a design that used
    parabolic mirrors, and there were various
    improvements in mirror-making. The Newtonian
    reflector was a highly successful design, and
    remains one of the most popular telescope designs
    in use today.

21
Reflecting telescopes focus light by bending them
with mirrors
22
Not everything is visible
www.yorku.ca/eye/spectrum.gif
  • Many modern day telescopes do not use visible
    light to collect images.
  • Radio telescopes, x-ray telescopes and infrared
    (IR) telescopes have become a staple of modern
    day astronomy, producing some amazing images.

23
Famous Telescopes
  • Keck Telescope
  • http//www.jpl.nasa.gov/events/lectures/dec04.cfm
  • Kitt Peak Observatory
  • http//www.jpl.nasa.gov/events/lectures/dec04.cfm

24
Very Large Array (VLA)radio telescopes
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