Download CHAPTER 3: Light and Telescopes

CHAPTER 3:
Light and
Telescopes
Electromagnetic Radiation
Only a very small range of wavelengths, 400nm to 700nm, are visible to humans.
Electromagnetic radiation waves, are fluctuations
of electric and magnetic fields, which move
through empty space at the speed of light
Wavelengths are very small so astronomers use
nanometers 10 -9 m or angstroms 10 -10 m
Wave Properties of Light
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Frequency f - number
of waves that arrive in a
given time
Wavelength λ - distance
between crests
Velocity v - distance
covered in one second
by a crest in a certain
direction
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fxλ=ν
velocity of light in a
vacuum c = 300,000km/s
fxλ=c
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.
The transparency of a material depends on the wavelength of
light. Earth’s atmosphere is relatively transparent to visible light
and radio waves, which are referred to as “windows” through
which we can view space from a ground-based telescope.
Particle Properties of Light
Radiating matter emits light in discrete chunks
of energy called QUANTA (photon)
 When atoms are excited they can jump up
energy levels- when they move back down
they give off photons with energy equal to the
amount it needs to loose
 Energy(photon) = hc/ λ
 h= (planck’s constant = 6.63 x1023 J s
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CRAB NEBULA
Optical
Ultra Violet
X-Ray
Radio
Multiwavelength Universe
Radiation Type
Temp.
Source
Gamma-rays
more than 108 (K)
accretion disks
around black holes
X-rays
106-108 K
gas in clusters of
galaxies, supernova
remnants; stellar
corona
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Ultraviolet
104-106 K
supernova remnants; very
hot stars
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Visible
103-104 K
planets, stars, some
satellites
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Infrared
10-103 K
cool clouds of dust and
gas; planets

Radio
less than 10 K
radio emission produced by
electrons moving in
magnetic fields
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