Download CHAPTER 3: Light and Telescopes

Discussion Questions
1. The primary purpose of building larger optical
telescopes on the Earth’s surface is to
a.
b.
c.
d.
increase the light-gathering power.
increase the magnification.
improve the resolution.
allow a wider range of wavelengths to be viewed.
2. Why was the Hubble Space Telescope placed in orbit?
a.
b.
c.
d.
Maintenance on the telescope is easier to do in Earth orbit than on the
Earth’s surface.
To be closer to the stars
To eliminate the distorting effect of the Earth’s atmosphere
To detect X-rays, which cannot penetrate the Earth’s atmosphere
3. How long does it take light to travel 3 ! 108 m?
a.
1 year
b.
8 minutes
c.
1 minute
d.
1 second
4. A light source has a frequency
of 2 ! 105 Hz. What is its
wavelength?
a.
0.67 ! 10"3 m
b.
1.5 ! 103 m
c.
6 ! 1013 m
d.
0.16 ! 10"1 3 m
5. A light source has a frequency
of 2 ! 1013 Hz. What region of the
electromagnetic spectrum is it in?
a.
Gamma ray
b.
Ultraviolet
c.
Visible
d.
Infrared
e.
Microwave
CHAPTER 3:
Light and
Telescopes
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WHAT DO YOU THINK?
What is light?
! What is the main purpose of a telescope?
! Why do stars twinkle?
! How hot is a “red hot” object?
! What color is the Sun?
!
You will discover…
discover…
•the connection between sunlight, radio waves, and other
kinds of electromagnetic radiation
•the debate over what light is, and how Einstein resolved it
•how telescopes collect and focus light
•why different types of telescopes are used for different
types of research
•what new generations of land-based and space-based
high-technology telescopes being developed can do
•how astronomers use the entire spectrum of
electromagnetic radiation to observe the stars and other
astronomical events
•how to tell whether an object in space is moving toward
or away from Earth
Prisms
Newton found that the prism itself does not add the colors
to the light, but that color is an intrinsic property of light.
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When light of a single color is passed through two slits, the
light from the two sources creates an interference pattern of
bright and dark regions. This shows that light is a wave.
In 1860, James Clerk Maxwell combined and unified the
current theories of electricity and magnetism and showed
that electric and magnetic fields should travel through
space together in the form of electromagnetic waves.
These waves are characterized by their wavelength,
the distance between two peaks in a wave.
There are a wide range of
wavelengths of electromagnetic
waves plotted on the
electromagnetic spectrum. We
classify these waves by their
source, use, or interactions with
other matter.
Only a very small range of
wavelengths, 400nm to 700nm, are
visible to humans. (Since these
wavelengths are small we describe
them in terms of nanometers
(10-9m) or Angstroms (10-10m).
Other wavelengths are classified as
Gamma Rays, X-Rays, Ultraviolet,
Infrared, Microwaves or Radio
waves.
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Ole Romer used two eclipses of one of Jupiter’s moons to
show that light does not travel infinitely fast and to measure
its speed. One can also use Maxwell’s equations to
calculate the speed of light.
The speed of light, denoted by the letter c, has since been measured to be
299,792.458km/s which we generally round to
c = 300,000 km/s = 186,000 mi/s
The Doppler Effect
Sources moving toward
the observer squeeze
light waves in front of
them, causing them to be
shorter. We call this a
blueshift.
Sources moving away
from the observer stretch
the light waves behind
them, causing them to be
longer. We call this a
redshift.
Einstein showed that light also behaves as a
particle. He found that light behaves as discreet
packets called photons. The energy of a photon
decreases with its wavelength and is calculated
by:
Photon energy =
Planck’
Planck’ s constant ! speed of light
wavelength
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