Astronomy
Chapter 5 Section 1,2,3 Outline
Section 1:
Optical Telescopes:
-
Telescope: Light bucket, captures as
many photons as possible from a given region of the sky and concentrate them into
a focused beam for analysis.
o
Optical telescopes are designed specifically
to collect the wavelengths that are visible to the human eye.
-
Refracting and Reflecting Telescopes:
o
Refraction is the bending of a beam of
light as it passes from one transparent medium into another.
o
Reflecting telescope uses a lens to
gather and concentrate a beam of light.
o
Prime focus is the primary mirror in a
reflection telescope.
-
Comparing Refractors and Reflectors:
o
Factors that tend to favor reflecting
instruments over refractors:
§ Light
must pass through the lens is a disadvantage of a refracting telescope.
§ As
light passes through the lens, some of it is absorbed by the glass. This causes
problems with visible radiation.
§ A
large lens can be quite heavy, and tends to deform under its own weight.
§ A
lens has two surfaces that must be accurately machined and polished.
-
Types of Reflecting Telescopes:
o
Newtonian Telescope:
§ Named
after Isaac Newton, light is intercepted before it reaches the prime focus and
then is deflected by 90o, usually to an eye piece at the side of the
instrument.
o
Cassegrain Telescope:
§ Named
after Guillaume Cassegrain, the point behind the primary mirror where the light
from the star finally converges is called the Cassegrain focus. Requires
starlight to be reflected b several mirrors.
Section 2:
-
Light-Gathering Power:
o
Collecting area:
§ The
total area capable of gathering radiation.
-
Resolving Power
o
Angular resolution:
§ The
factor that determines our ability to see fine structure.
o
Diffraction:
§ The
tendency for light to bend around corners
o
Diffraction-limited resolution:
§ The
amount of diffraction increases in proportion to the wavelength used, and
observations in the infrared or radio range are often limited by its effects.
Section 3:
-
Image Acquisition:
o
Charge-coupled devices (CCD’s):
§ Electronic
detectors that aquire data of stars, they lead directly into computers.
o
Pixels:
§ Tiny
picture elements, they make up an image.
-
Image Processing:
o
Background noise:
§ Anything
that corrupts the integrity of a message, such as static on an AM radio or the “snow”
on a TV screen.
-
Wide-angle Views:
o
Large reflectors are very good at
forming images of narrow fields of view, wherein tall the light that strikes
the mirror surface moves almost parallel to the axis of the instrument.
-
Photometry:
o
Telescopes act as high power cameras
when a CCD is placed at their focus.
o
Photometry:
§ The
measurement of brightness.
o
Photometer:
§ A
device that records highly accurate and rapid measurements of light.
-
Spectroscopy:
o
Spectrometers:
§ Devices
that read the spectrum of light given off by stars and light.
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