24.1 The Study of Light
Electromagnetic Radiation
 Includes gamma rays, X-rays, UV light, visible
light, infrared radiation, microwaves, & radio
waves
 Electromagnetic Spectrum
 Classifies radiation according to wavelength &
frequency
 Photons – small packet of light energy
 Copy diagram on pg. 674 fig. 1
Spectroscopy
 The study of the properties of light that depend on
wavelength
 Continuous spectrum – produced by an incandescent solid,
liquid, or gas under high pressure (emit when hot)
 Absorption spectrum – produced when visible light is
passed through a relatively cool gas under low pressure.
(gas absorbs selected wavelengths of light)
 Emission Spectrum – produced by a hot gas under low
pressure (bright lines)
 When the spectrum of a star is studied, the spectral lines act
as “fingerprints”
The Doppler Effect
 Occurs for both sound and light
 Change in wavelength of a wave that is emitted
from a source that is moving away or toward an
object
 Light source that is moving away = redder
 Light source that is moving toward = blue
 Doppler Effect is used to determine whether a star
or other body in space is moving away from or
toward Earth
REVIEW REVIEW
REVIEW
 What types of radiation make up the
electromagnetic spectrum?
 Compare the 3 types of spectra
 How are the elements in a star determined?
 How can the Doppler Effect tell detection?
24.2 Tools for Studying
Space
Refracting Telescopes
 Bend or refract light
 Objective lens produces an image by bending
light from a distant object so that the light
converges at an area called the focus (central pt.)
 Chromatic aberration ( color & to go astray)
 Property of a lens whereby light of diff. colors is
focused at diff. places (produces a halo around it)
 Blue light is in focus = reddish halo
 Red light is in focus = bluish halo
https://www.youtube.com/watch?v=VzSjqNE2AHM
Reflecting Telescopes
 Chromatic aberration is avoided
 Use a concave mirror that focuses light in front
of a mirror rather than behind
 Most large optical telescopes are reflectors
 Light does not pass through a mirror so the glass
for a reflecting telescope does not have to be of
optical quality
https://www.youtube.com/watch?v=ic2aPxePlEs
Properties of Optical
Telescopes
 Both refracting & reflecting telescopes have 3
properties that help astronomers
 Light gathering power
 Resolving power
 Magnifying power
Detecting Invisible Radiation
 Radio telescopes – focuses the incoming radio waves
on an antenna which absorbs & transmits these
waves to an amplifier just like a radio antenna
 Poor resolution (-)
 Less affected by turbulence than optical telescopes
(+)
 Radio telescopes are hindered by human made radio
interference (hidden in valleys to block these types
of interference)
Space Telescopes
 Orbit above Earth’s atmosphere & produce
clearer images than Earth-based telescopes
 Hubble Space Telescope
 1st space telescope built by NASA
REVIEW
 How does a refracting telescope work?
 Compare and contrast a refracting telescope and
a reflecting telescope
 How do radio telescopes gather data?
 Why do space telescopes obtain clearer images
than Earth based telescopes?