Chp 5.1-5.3 Outline

5.1

• Optical Telescope- Optical is designed specifically to collect the wavelengths that are visible to human eye.
• Telescope-device designed to collect as much light as possible from some distant source and deliver it to a detector for a detailed study. Depending on the size and power of the telescope one can see several thousand light years into space.
• Refracting Telescope- uses a lense to concentrate and focus the light captured by the telescope.
• Reflecting Telescopes- use mirrors to reflect the image.
• Newtonian and Cassegrain- reflecting telescopes that use secondary mirrors to avoid placing detectors at the prime focus. More complex light paths are also used to allow the use of large or heavy equipment that cannot be plaved near the telescope.

5.2

• All large astronomical telescopes are reflectors because large mirrors are lighter and easier to consturct than large lenses. They also suffer fewer defects and do not need to be replaced or cleaned as often as lenses.
• The collecting area, which is the light gathering power of a telescope, is proportional to the square of the mirror diameter.
• To study the faintest sources of radiation, astronomers must use very large telescopes. They suffer least from the effects of diffraction and are able to better achieve better angular resolution once the blurring effects of Earth's atmosphere are overcome.
• The amount of diffraction is proportional to the wavelength of the radiation under study and inversley proportional to the size of the mirror.

5.3

• Most modern telescopes use charge-coupled devices (CCD's) instead of photographic plates to collect their data.
• The field of view is divided into an array of millions of picels that accumulate an electric charge when light strikes them.
• CCD's are much more sensitive than photographic plates, and are more easily saved into the computer and are much more popular in the astronomical field.
• Photometry may be performed either on a stored image or during the observations, using a specialized detector called a spectrometer, that may be used to analyze the spectrum of the radiation recieved.