Astronomy 1010-H
Planetary Astronomy
Fall_2015
Day-18
Exam Sadistics
Ex-1
Ex-2
N
Ave. 58.5
Stdev
Median
Mode
High 91
Low 31
70
72
56.1
14.8
57.5
49
16.3
56
61
94
23
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; Ch. 3, 4, & 5
•
SW-chapter 4 posted: due Today
SW-chapter 5 posted: due Fri. Oct. 9
•
Definitions & Terms -1
•
•
•
•
Excitation: The process of an electron absorbing a
photon, gaining energy.
De-Excitation : The process of an electron losing a
photon, losing energy.
Ionization: The process of an atom losing an
electron due to absorbing too much energy.
Recombination : The process of an atom
capturing an electron as it loses energy.
Photons
 Light also behaves as a particle.
 Photon: particle of light.
 Photons carry energy and can have
different amounts of energy.
 Photons with high energy = light with high
frequency.
 Photons with low energy = light with low
frequency.
 Atoms can absorb or emit photons.
 Atoms have a dense nucleus of protons and
neutrons.
 Electrons surround the nucleus in a “cloud.”
 Electrons can have
certain energies;
other energies are not
allowed.
 Each type of atom
has a unique set of
energies.
 Energy level diagram
represents this.
 Lowest energy is the
ground state.
 Emission: An
electron emits a
photon and drops to
a lower energy state,
losing energy.
 The photon’s energy
is equal to the
energy difference
between the two
levels.
 Absorption: An
electron absorbs the
energy of a photon,
moving the electron
to a higher energy
level.
 The photon’s energy
has to be equal to
the energy
difference between
the two levels.
 The spectrum of
a cloud of
glowing gas
contains
emission lines.
 When viewed
through a cloud
of gas, a
continuous
spectrum will
have absorption
lines.
 The wavelengths at which atoms emit and
absorb radiation form unique spectral
fingerprints for each atom.
 They help determine a star’s composition,
temperature, and more.
MATH TOOLS 5.1
 Knowing the speed of light and one other
variable, either the wavelength or frequency
of the light in question, you can find the
remaining quantity.
 Example: Find the wavelength of the light
wave coming from a radio station
broadcasting on 770 AM:
Lecture Tutorial
Light & Atoms: (pg. 65)
• 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—Energy Levels
In the energy level diagram, transition B has half the
energy of transition A. What is the wavelength of emitted
light?
A. 225 nm
B. 450 nm
C. 900 nm
B:  = ?
A:  = 450 nm
 The motion of a light source toward or away
from us changes our perception of the
wavelength of the waves reaching us.
 Doppler effect.
 Light from approaching objects is
blueshifted; the waves crowd together.
 Light from receding objects is redshifted;
the waves are spaced farther apart.
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
D
v

0 c
D = wavelength shift
o = wavelength if source is not moving
v = velocity of source
c = speed of light
MATH TOOLS 5.2
 If you know the wavelength of light you are
observing as well as the wavelength of light
the object would be emitting if it were at rest,
you can find the speed of the object using
the Doppler effect.
Concept Quiz—Doppler Shift
Hydrogen emits light at  = 656 nm. You see
a distant galaxy in which the light from
hydrogen has  = 696 nm.
This galaxy is
A. moving toward us.
B. moving away from us.