Telescopes use either refraction or reflection to collect and focus light. Refracting telescopes use convex lenses to bend light, while reflecting telescopes use concave mirrors. Major components of telescopes include the primary mirror or lens, diagonal mirror, aperture, filters, and charged-coupled devices (CCDs) that capture images digitally. Telescopes allow astronomers to see faint objects by gathering more light and forming focused images.

1. DETECTING,
COLLECTING &
FOCUSING LIGHT

3. Telescope
The main purpose of a
telescope is to capture
more light and see
fainter objects than our
eyes allow us to see.

4. Telescopes come in many
different varieties but
they all boils down into
two major principles.
Refracting and
Reflecting of light.

5. Refracting Telescope
A refracting telescope
uses a convex mirror
(the center is thicker than
the edges) to focus light.

6. The refraction properties
of glass (the way it bends
light) are used to gather
parallel rays of light and
focus them to a point. The
image is created at the
focal point of the telescope.

10. Reflecting telescope
A reflecting telescope
uses a concave mirror
instead of convex mirror
to collect and focus light.

11. A large concave mirror
(the center is thinner
than the edges) collects
and reflects the light to
make an image.

12. Reflecting telescopes can
see objects that are a
millionth or a billionth the
brightness of the faintest
star that can be seen by the
human eye alone.

16. Objective/
Primary Mirror
The large, concave, lightgathering mirror in a
reflecting telescope.

18. Diagonal/
Secondary Mirror
In a reflecting telescope,
a mirror that directs the
light from the primary
mirror to a focal position.

20. Cassegrain Telescope
A type of reflecting
telescope in which
incoming light hits the
primary mirror and is then
reflected upward toward
the prime focus,

21. where a secondary mirror
reflects the light back
down through a small hole
in the main mirror into a
detector or eyepiece.

23. Newtonian Telescope
A reflecting telescope designed
so that the focused light is
reflected by a small secondary
mirror out to the side of the
telescope, where it can be
viewed.

25. Aperture
The opening in a telescope
or other optical instrument
that determines how much
light it collects.

26. The size of the diaphragm
opening in a telescope’s lens
regulates amount of light
passes through onto the film
inside the camera the moment
when the shutter curtain in
telescope opens during an
exposure process.

29. Lens
An optical instrument, made
of glass or some other
transparent material, shaped
so that parallel rays of light
passing through it are bent to
arrive at a single focus.

31. Filter
Color filters are usually
constructed using transparent
pieces of dyed glass, plastic,
lacquered gelatin (e.g. Wratten
filters) that have been treated to
selectively transmit the desired
wavelengths while restricting
others

33. The two most
common types of
filters in use today

34. Absorption Filters
Absorb unwanted
wavelengths.
They are used to create special
effects in a number of
photography applications and
are widely employed in the
cinema industry.

35. In addition, absorption
filters are commonly found
in signs and traffic signals
and as directional signals
on automobiles, boats, and
airplanes.

37. Interference Filters
Remove selected
wavelengths by internal
destructive interference
and reflection.

38. These filters differ from
absorption filters in the
fact that they reflect and
destructively interfere with
unwanted wavelengths as
opposed to absorbing
them.

40. CCD
Charged-coupled device:
an electronic device that
records the intensity of light
falling on it. Have replaced
film in most astronomical
applications.

41. When you take a picture
with a digital camera, the
image is recorded by a
sensor, called a "charged
coupled device" or CCD

45. Focal Plane
The surface where the
lenses and/or mirrors of a
telescope form an image of
a distant object.

47. Focus
Also called an image
point, a point in an optical
system in which light rays
are brought together; the
location where an image
forms in such systems.

50. Coherent
A relationship indicating
that electromagnetic waves
are in synchronization with
each other. Waves that are
coherent exhibit persistent
interference effects.

52. Chromatic Aberration
A distortion of an
optical system that results
in different colors not
focusing in the same way,
often producing color
fringes or distorted shapes.

55. Dispersion
The spreading of light
or other electromagnetic
radiation into a spectrum.
A rainbow is an example of
the dispersion of light
caused by raindrops.

57. False-color image
A depiction of an
astronomical object in
which the colors are not
the object's real colors.

58. Instead, they are colors
arbitrarily chosen to
represent other properties
of the body, such as the
intensity of radiation at
other than visible wave
lengths.

64. Photoelectric Effect
Emission of electrons
from a material when light
of a high-enough frequency
strikes it.

65. Regardless of the
brightness of the light, no
electrons are emitted
unless the photons' energy
is greater than a value that
depends on the material.

68. Pixel
The term "pixel" is
actually short for "Picture
Element." These small
little dots are what make
up the images on computer
displays.

69. The screen is divided up
into a matrix of thousands
or even millions of pixels.
Typically, you cannot see
the individual pixels,
because they are so small.

72. Surface Brightness
The overall brightness
of an
extended astronomical
object such as a galaxy, star
cluster, or nebula.

73. Ex: a galaxy with a high
density of stars will have a
high surface brightness,
but one with the same
number of stars more
widely spread out will have
a lower surface brightness.

75. THE END!
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