Light and Telescopes

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Slide 39

A refracting telescope uses a lens to concentrate incoming light

Slide 40

Slide 41

A larger objective lens provides a brighter (not bigger) image

Slide 42

lenses reverse images

Slide 43

Three main functions of a telescope

Brighten

(called light gathering power)

See fine detail

(called resolution)

and least important,

Magnify

magnification = (objective lens focal length / eyepiece lens focal length)

Slide 44

Functions of a Telescope

To gather light.

want a large objective

range of few inches to 10 meters!!

To resolve fine detail.

limited by size and atmospheric “seeing”

To magnify

least important

about 50x per inch of aperture (rule of thumb)

Slide 45

Refracting telescopes have drawbacks

Spherical aberration

Chromatic aberration

Slide 46

Slide 47

Refracting telescopes have drawbacks

Spherical aberration

Chromatic aberration

Sagging due to gravity distorting the lens

Unwanted refractions

opaque to certain wavelengths of light

Yerkes Observatory - 40-inch Refracting Telescope: The Largest Refracting Telescope in the World

Slide 48

Reflecting telescopes use mirrors to concentrate incoming starlight

Slide 49

Slide 50

Astronomer’s face two major obstacles in observing the stars

Light Pollution from Cities

Effects of Twinkling from Earth’s atmosphere

Slide 51

Tucson, Arizona in 1959 and 1980

Slide 52

Earth’s atmosphere hinders astronomical research

Slide 53

Rapid changes in the density of Earth’s atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle.