Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-17
Course Announcements
•
How is the sunset/sunrise observing going?
•
Dark Sky nights – Mon. 10/5 & Wed. 10/7 starting at
7:30pm – at the Observatory.
•
Exam-2 will be Friday, Oct. 9
•
SW-chapter 4 posted: due Mon. Oct. 5
SW-chapter 5 posted: due Fri. Oct. 9
•
Definitions & Terms -1
•
Light: The primary source of information in
astronomy for all objects. When we say “light” we
are talking about everything from gamma-rays to
radio-waves. This does NOT include gravity waves.
 Gravitational objects create Roche limits
within which the effects from their tidal forces
can destabilize other objects.
 Planets, stars, and galaxies can be affected.
 Galaxies can be distorted with tidal tails.
 Moons of planets can have great internal
activity because of tides, perhaps allowing for
conditions for life.
MATH TOOLS 4.3
 In order to leave a planet’s surface, an
object must achieve a velocity greater than
the planet’s escape velocity.
 Therefore, Earth’s escape velocity is
MATH TOOLS 4.4
 The net tidal force is the difference in force
on the two sides of the planet.
 The Moon’s tidal forces on Earth are 2.2
times as strong as the Sun’s tidal forces
on Earth, resulting in greater lunar tides
than solar tides.
 Almost all
knowledge of the
universe beyond
Earth comes from
light.
 Light can tell us
about objects in
space: temperature,
composition,
speeds, and more.
 Light moves at 300,000 km/s in a vacuum.
 First measured by Rømer when observing
Jupiter’s moons.
 Speed is slower in other materials, e.g.,
glass.
 Light is a wave of combined electricity and
magnetism, called an electromagnetic wave.
 Changing electric and magnetic fields create a
self-sustaining electromagnetic wave.
 Wavelength ():
length between
crests.
 Amplitude: height.
 Frequency (f):
number of waves
that pass by each
second.
 Period (P): time to
complete one cycle.
 A long wavelength
means low
frequency.
 A short wavelength
means high
frequency.
 The speed of light, c,
is constant.

S
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d
c
W
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l
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n
g
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
o
r
F
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f
 Visible spectrum:
small range of
wavelengths that
humans can see.
 Red light = longest
wavelength
( ~ 750 nm).
 Violet light = shortest
wavelength
( ~ 380 nm).
 “Roy G. Biv.”
 Visible light is just one small part of the
electromagnetic spectrum:
Gamma rays X-rays UV Visible IR Microwave Radio

increasing
f
decreasing
Lecture Tutorial
EM Spectrum: (pg. 47)
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with
one another. Take time to understand it
now!!!!
• Come to a consensus answer you both agree
on.
• If you get stuck or are not sure of your answer,
ask another group.
Concept Quiz—AM and FM
On the FM dial, the frequencies run from 88 to 107 MHz
(million cycles per second). On the AM dial, the range is
570 to 1600 kHz (thousand cycles per second). Which
statements are true?
A.
B.
C.
D.
FM photons have shorter wavelengths than AM.
FM photons have higher energies than AM.
FM photons travel at the same speed as AM.
All the above statements are true.