Download APSU_1000_35 Liberal Arts Univ. Life

ASTR-1010
Planetary Astronomy
Day - 17
Announcements
Homework Chapter 3: Due Today
Smartworks Chapters 4: Due Monday, March 1.
Smartworks Chapter 5 is also posted
Exam 2 will cover chapters 3, 4, & 5
-Target Wednesday, March 3
1st quarter observing night: Tonight!
7:30pm
ClassAction Stuff
• Hydrogen atom simulator
• EM Wave demo
Tutorial:– p.63
Light & Atoms
• 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.
• Work with a partner!
• 5 minutes
Each chemical element produces its own unique
set of spectral lines when it is excited
The type of spectrum given off depends
on the objects involved
Law #1 – The excited atoms within a hot
dense object give off light of all colors
(wavelengths) and produce a continuous
spectrum -- a complete rainbow of colors
(range of wavelengths) without any spectral
lines.
We will study three types of spectra!!!
Hot/Dense Energy Source
prism
Continuous Spectrum
The type of spectrum given off depends on
the objects involved
Law #2 – The excited atoms within a hot,
cloud of gas give off only particular colors
(wavelengths) of light and produce an
emission line spectrum - a series of
bright spectral lines against a dark
background.
We will study three types of spectra!!!
Hot low density cloud of Gas
prism
Emission Line Spectrum
The type of spectrum given off
depends on the objects involved
Law #3 – When the light from a hot dense
object passes through a cool cloud of gas, the
atoms within the cloud can absorb particular
colors (wavelengths) of light and produce a
absorption line spectrum - a series of dark
spectral lines among the colors of the rainbow.
We will study three types of spectra!!!
prism
Hot/Dense Energy Source
Cooler low density cloud of Gas
Absorption Line Spectrum
We will study three types of spectra!!!
prism
Hot/Dense Energy Source
Continuous Spectrum
prism
Hot low density cloud of Gas
Emission Line Spectrum
prism
Hot/Dense Energy Source
Cooler low density cloud of Gas
Absorption Line Spectrum
ClassAction Stuff
• 3 View spectrum animation
• Blackbody demonstrator
• Light & Filters
All objects emit radiation.
For objects of same size:
- the peak intensity drops
with temperature;
- the wavelength of
maximum intensity
moves to the red (longer)
with falling temperature.
What physical situation does a
star like the sun present?
A hot dense core
surrounded by a low
density atmosphere.
Why is this important in
planetary astronomy?
Planets reflect starlight.
The Sun’s Spectrum
The Doppler Effect
• Definition: “The change in wavelength of
radiation (light) due to the relative motion
between the source and the observer
along the line of sight.”
Astronomers use the Doppler Effect to learn
about the radial (along the line of sight) motions
of stars, and other astronomical objects.
Real Life Examples of Doppler Effect
• Doppler Radar (for weather)
• Airplane radar system
• Submarine radar system
– Ok, anything with radar
• Radar gun, used by Law Enforcement
Doppler Shifts
• Redshift (to longer wavelengths): The source
is moving away from the observer
• Blueshift (to shorter wavelengths): The source
is moving towards the observer
Dl
v

l0 c
Dl = wavelength shift
lo = wavelength if source is not moving
v = velocity of source
c = speed of light
Doppler Effect
• When the source of light is moving away from
the observer the wavelength of the emitted light
will appear to increase. We call this a “redshift”.
Doppler Effect
• When the source of light is moving towards the
observer the wavelength of the emitted light will
appear to decrease. We call this a “blueshift”.
Doppler Effect
• “Along the line of sight” means the
Doppler Effect happens only if the object
which is emitting light is moving towards
you or away from you.
– An object moving “side to side” or
perpendicular, relative to your line of sight,
will not experience a Doppler Effect.
Doppler Effect
• When something which is giving off light moves
towards or away from you, the wavelength of
the emitted light is changed or shifted
V=0
Astronomy Application
V=0
Doppler Shift
Lecture Tutorial pg. 73
• Do this one to learn more … it’s normally
done in the stellar class, but has
application s to planetary astronomy.
ClassAction Stuff
• Doppler Shift Animation
• Radial Velocity demo
• Splash page questions