Lab3_Light_and_Telescopes
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University of Southern California *
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343M
Subject
Astronomy
Date
Dec 6, 2023
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docx
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8
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Name
: Eric Chung
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Date
: 2/18/2023
LIGHT & TELESCOPES
Activity 1: Waves
Astronomers use light to study celestial objects, but the light comes in many forms.
The
most familiar form is visible light, the form of electromagnetic radiation that we can see.
The full spectrum of electromagnetic radiation extends to much longer and too much
shorter wavelengths that we can see, however.
Radio waves, microwaves, infrared,
visible, and ultraviolet light, x-rays, and gamma rays are all forms of electromagnetic
radiation.
Light is an example of a wave, and there are many types of waves in nature.
Examples
of familiar waves are water waves, sound waves, and light waves (and don’t forget
gravity waves!).
Waves are characterized by three parameters: wavelength, frequency
(waves per second), and speed, and these properties are related by a simple
expression. (See module: Nature of Light)
Speed = Wavelength x Frequency
Speed is measured as distance traveled per second.
Wavelength is the length of a wave from peak to peak.
Frequency is the number of waves per second that pass a given point.
Example 1
:
What is the wavelength of a typical sound wave?
The frequency of, say,
middle C is about 256-278 cycles per second depending on the scale, and sound
travels at about 340 meters per second.
F1 = 256 Hz
F2 = 278 Hz
V = 340 m/s
W1 = V/f1 = 1.32 m
W2 = V/f2 = 1.22 m
It’s between 1.328 and 1.223 meters.
Example 2
: A tsunami wave travels at a speed of about 0.2 meters/second, with a
wavelength of about 50,000 m.
What will be the time between peaks of a tsunami wave
coming ashore on the beach?
V = 0.2 m/s
w = 50,000 m
1
f = V/w = 4 x 10^-6 Hz
The time between peaks is 0.000004 Hertz.
Example 3
:
Electromagnetic waves travel with speed of about 300,000 km per second
(3 x 10
8
meters per second).
What is the wavelength of an electromagnetic wave with a
frequency of one billion cycles per second (10
9
cycles per second). What kind of light is
this?
V = 3 x 10^8 m
f = 10^9 Hz
w = V/f = 0.3 m >> radio light (radio wave)
The wavelength is 0.3 meters. This type of light is called radio light, or radio waves.
Example 4
:
Gravity waves also travel at the speed of light (3 x 10
8
meters per second).
Two neutron stars, each with mass equal to two solar masses, orbiting each other with a
separation of 0.63 light seconds and a period of 750 seconds (frequency = 0.0013 per
second), will emit gravity waves.
What is the wavelength of these gravity waves?
V = 3 x 10^8 m/s
f = 0.0013/s
W = S/f = 2.31 x 10^12
It’s 2.308 x 10^12 meters.
Gravitational waves (or gravity waves) are disturbances or ripples in the curvature of
spacetime, generated by accelerated masses, that propagate as waves outward from
their source at the speed of light. In general, gravitational wave frequencies are much
lower than those of the electromagnetic spectrum (a few thousand hertz at most,
compared to some 10
16
to 10
19
Hz for X-rays). Consequently, they have much larger
wavelengths – ranging from hundreds of kilometers to potentially the span of the
Universe.
Activity 2: Analyzing Infrared Images
Examine the three pairs of optical and infrared images of the Old Faithful geyser in
Yellowstone National Park (Old Faithful is the most frequently erupting large geyser in
the park). A geyser is a hot spring which erupts periodically.
These eruptions are
caused by the buildup of hot water and steam trapped by constrictions in the "plumbing
system" of a hot spring.
When enough pressure builds up the geyser erupts.
The three
image pairs are a time sequence from the beginning to the end of the geyser’s eruption.
The infrared images are shown in “pseudocolor” since our eyes cannot see infrared
light.
Color corresponds to temperature with the hottest parts of the image shown as
white light and the coolest parts shown as black.
2
1.
Which regions of the image are the coolest?
From black to blue are the coolest. This is where the geyser is actively erupting.
2.
Which regions are the hottest?
From yellow to white are the hottest. This is where the geyser is not erupting.
3.
Do the infrared images give you information that you cannot get from the visible light
images?
Yes, they let us see temperature differences within images. This allows us to know how
hot the geyser’s eruption is.
4.
Describe the difference between pseudo color and true color.
In what circumstances
would pseudo color be useful?
Pseudo color lets us visualize things that we cannot see with our own eyes. Pseudo
color is helpful when needing to document such aspects like the temperature of the
geyser. True color is the actual colors of objects as seen by our naked eye.
5.
What would astronomers learn from observations of astronomical objects in infrared
light, compared to observations in visible light?
They can learn the temperatures of celestial objects or regions, and cross reference that
with others. Infrared can also be used to study wavelengths, stars, invisible to the
human eye, and more.
Visible Light Images
Infrared Images
3
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