Transcript Tools for Studying Space

Warm Up 5/29/08
1)
2)
3)
What does a prism do?
a. separates sunlight into ultraviolet and infrared
radiation
b. separates visible light into several colors
c. changes the wavelength of electromagnetic waves
d. combines the colors of visible light into white light
What will happen to an object’s wavelength as the
object moves toward you?
a. The wavelength will vary.
b. The wavelength will be shortened.
c. The wavelength will not change.
d. The wavelength will be lengthened.
Large Doppler shifts indicate ____.
a. high speeds
c. low speeds
b. low temperatures
d. high temperatures
Answers: 1) b. 2) b. 3) a.
Tools for Studying Space
Chapter 24, Section 2
Refracting Telescopes





Refracting Telescope – a telescope that uses a
lens to bend and concentrate the light from
distant objects
The most important lens in a refracting telescope,
the objective lens, produces an image by bending
light from a distant object so that the light
converges at an area called the focus
For an object such as a star, the image appears
as a point of light; for nearby objects, it appears
as an inverted replica of the original
Astronomers usually study an image from a
telescope by first photographing the image
Chromatic Aberration – the property of a lens
whereby light of different colors is focused at
different places
Simple Refracting Telescope
Concept Check
What is chromatic aberration?
 Chromatic aberration is an effect
associated with refracting telescopes
that weakens an image and produces
a halo of color around it.

Reflecting Telescopes






Reflecting Telescope – a telescope that
concentrates light from distant objects by using a
concave mirror
Because the focus of a reflecting telescope is in front
of the mirror, an observer must be able to view the
image without blocking too much incoming light
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
Both refracting and reflecting telescopes have three
properties that aid astronomers in their work: 1)
light-gathering power, 2) resolving power, and 3)
magnifying power
Another advantage of telescopes with large
objectives is their great resolving power, which
allows for sharper images and finer detail
To find the magnification, divide the focal length of
the objective by the focal length of the eyepiece
Viewing
Methods with
Reflecting
Telescopes
Concept Check
What is light-gathering power?
 Light-gathering power refers to the
telescope’s ability to intercept more
light from distant objects, thereby
producing brighter images.

Detecting Invisible Radiation






A narrow band of radio waves is able to penetrate
the atmosphere, by measuring these waves we can
map the galactic distribution of hydrogen
Radio Telescope – a telescope designed to make
observations in radio wavelengths
A radio telescope focuses the incoming radio waves
on an antenna, which absorbs and transmits these
waves to an amplifier, just like a radio antenna
Large dishes are necessary to intercept an adequate
signal from celestial sources
Radio telescopes are less affected by turbulence in
the atmosphere, clouds, and the weather; viewing is
possible 24 hours a day; they can “see” through
interstellar dust clouds that obscure visible
wavelengths
Radio telescopes have revealed spectacular events
(the collision of two galaxies!)
Radio Telescopes
Concept Check
Why can radio telescopes be used 24
hours a day?
 They do not need visible light to
obtain images.

Space Telescopes





Space telescopes orbit above Earth’s
atmosphere and thus produce clearer
images than Earth-based telescopes
The first space telescope, built by NASA,
was the Hubble Space Telescope (put into
orbit in 1990)
Hubble and other telescopes have detected
more than 140 extrasolar planets (a planet
orbit around a star other than the sun)
A planet’s gravity causes a Doppler shift in
light emitted by the planet’s star
Space telescopes are designed often to
observe objects in space at wavelengths
outside the visible spectrum; this allows
astronomers to classify objects and to
study how they formed
Hubble Space Telescope
Assignment


Read Chapter 24, Section 2 (pg. 678-683)
Do Chapter 24 Assessment #1-34