The Cosmic Perspective Chatper 6: Telescopes

Telescopes

Collects data about the universe

Lens

transparent cartilage that bends light to form an image on the retina

retina

light sensitive cells located at the back wall of the eye

pupil

controls how much light enters the eye

focus (focal point)

parallel rays of light converge to a point

focal plane

where the image appears in focus, on the eye this is located on the retina

Film/Digital aperature

controls amount of light that enters lens

shutter

curtain; made of thin metal, can be timed to allow more photos

exposure time

amount of time light is allowed to let through, controlled by shutter

Changed couple device (ccd)

Silicon chip, grid like pattern, allowed digital photography to go forward

Pixels

Electronic chips that are physically divided into grids of picture elements

Image processing

images that have been combined and manipulated through techniques.

Light collecting area

Tells how much light can be collected from a telescope at one time

- a small increase in diameter allows for a bigger light collection.

Angular resolution

Tells us how much detail we can see in a telescopes image

- higher resolution shows better detail.

Interference

Limit telescopes angular resolution even when all other conditions are perfect.

- can cancel information

Diffraction limit

Effects of interference that limit telescope resolution, depends on both the diameter of the telescopes primary mirror and the wavelength of the light being observed

Refracting telescope

Works like an eye, uses glass lenses to focus light, held up to the eye and look through it.

- needs to be aimed precisely, very sensitive because of exposure to ambient temperature.

Imaging

use photographs of astronomical objects

Reflecting telescopes

Uses curved mirrors instead of glass lenses , all that matters is the surface . Uses primary and secondary mirror.

Filters

Placed in front of a camera to allow particular colors or wavelengths of light to pass through

Spectroscopy

Breaking down waves of light, identify chemical compositions, temperature, and movemnt on distant objects

Spectrograph

breaks light up into its colors

Timing

Objects in sky where brightness varies, times rotation of planets by light curves

Light pollution

The atmosphere scatters light, is human made, you can't see many stars, can hinder astronomical observations

Turbulence

Moving currents of air, stars don't really twinkle

Dark location:

Area where there is minimal light pollution

Dry location

Limited clouds and rain

Calm location

Limited turbulence

High location

Above the densest part of the atmosphere

Adaptive optics

Can eliminate blurring, allows telescopes to to achieve angular resolution close to diffraction limit

Interferometry

Link 2 or more individual telescopes to achieve angular resolution of a much larger telescope

Radio telescope

Most common type of telescope in the world

- essentially it is a satellite dish designed to collect radio waves from a satellite in Earth orbit

Infrared telescope

Limited by the Earth's atmosphere, information can be collected from a visible light telescope , wavelengths do not reach the ground, can only be measured from higher elevations

Ultraviolet telescope

Can be collected and focused by visible light mirrors, Earth's atmosphere completely absorbed that making most observations impossible from the ground

X-ray telescopes

Has sufficient energy to penetrate many materials including living tissue an ordinary mirrors , uses special mirrors called grazing incidence mirrors so rays graze their surfaces as they are deflected toward the focal plane