Transcript Telescopes - Year9LightEffects

Telescopes
A telescope is an instrument specifically designed to
view remote objects through use of
electromagnetic radiation. The most common
type of telescope is the optical telescope, which
operates through gathering and focusing light
from the visible part of the electromagnetic
spectrum.
Some telescopes work in infrared light or in
ultraviolet. Optical telescopes enhance the
brightness of distant objects and the angular size.
Electromagnetic Spectrum
The electromagnetic spectrum is the range of
every possible frequency in electromagnetic
radiation. The electromagnetic spectrum of
an object is determined by the certain
distribution of radiation both emitted and
absorbed by the object.
How it Works
So that the optical telescope can receive,
observe, photograph, study and send images
to a computer, it employs a variety of optical
elements such as glass – lenses or mirrors to
gather light and other electromagnetic
radiation to bring the said light and radiation
to a focal point.
The basic light gathering element, the objective
(the convex lens or concave mirror used to
gather incoming light) focuses that light from
the distant object to a focal plane where it
forms a real image. This image can then be
recorded or viewed through an eyepiece,
which acts like a magnifying glass. We then
see an inverted, magnified virtual version of
the real object.
Inverted Images
Most telescopes use a system of inverted
images, produced at the focal plane. These
are called inverting telescopes. In
astronomical telescopes the inverted view
usually stays uncorrected for it doesn’t affect
the way the telescope is used.
Real and Virtual Images
A virtual image is created when the outgoing beams of light
from a point on the object do not actually intersect, or
meet, at a point. An example of this is looking at yourself in
front of a flat mirror and perceiving the image to be at a
doubled distance away from you. If you look into a mirror
and are standing a metre from the mirror, your reflection
will appear to be two metres away.
A real image, on the contrary, is a representation of the
object, in which the perceived location of the object is a
meeting of the rays of light that make up the image. An
example is of the images seen on a cinema screen. The
source is the projector and together with the rear camera
detector produces an image, which is then produced on the
human retina.
Types of Telescopes
Telescopes are often used in astronomy. There
are three main types:
The Refracting Telescope
It uses lenses to form an image. The refracting
telescope uses an objective lens and a type of
eyepiece together to collect more light than the
human eye could gather unaided. It focuses the
light onto a focal plane and gives the viewer a
clearer, brighter and larger picture of the object, a
magnified virtual image.
The Reflecting Telescope
It uses a collection of mirrors to form the image.
Light bounces off a large concave mirror, which
in turn focuses the light on a secondary mirror.
The most common type of focus is Coude’s
focus. This method uses two extra mirrors to
reflect the image outside of the telescope, so
that the image can be seen through a lens or
photographed.
The Catadioptric Telescope
This uses both a combination of lenses and
mirrors to form an image; the lens might
be in front of the mirror or somewhere
along the optical path to create the
image. If used in a prime focus
configuration they can have a very wide
coma free field of view.
The End