ASTR1030 - FALL, 2008. LECTURE 11; PAGE 1
ASTR1030
Announcements
http://lasp.colorado.edu/~ergun/
ASTR1030/
Next Observing: Thursday, Oct. 2, 7:30 pm. SBO.
Pick Up Midterms
• This weeks reading: Chapter 6.
Today
• Review and finish orbits.
• Light.
Prepare for your exams
Study with the several resources on Docsity
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Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
ASTR1030 Lecture 11: Orbits and Light - Prof. Robert E. Ergun, Study notes of Astronomy
The slides from lecture 11 of the astr1030 course at the university of colorado boulder, focusing on changing orbits and the wave-particle duality of light. It includes formulas for calculating escape velocity, information about the solar system and light spectrum, and the interaction of light with matter.
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ASTR1030 - FALL, 2008. LECTURE 11; PAGE 1
ASTR
Announcements
http://lasp.colorado.edu/~ergun/
ASTR1030/
Next Observing: Thursday, Oct. 2, 7:30 pm. SBO.
Pick Up Midterms
- This weeks reading: Chapter 6.
Today
- Review and finish orbits.• Light.
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 2
ASTR1030 Midterm 1 Scores
10
20
30
40
50
60
70
80
90
AVERAGE = 79MEDIAN
12 10
(^8642)
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 4
Changing Orbits
Example: How fast must a spacecraft go to escape Earth?
v
GM
r
×
×
×
× 6.
×
m --- s
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 5
Changing Orbits
Sun
Mar’s Orbit
Earth
1.5 AU 1 AU
Satellite path.
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 7
Light: The “Wave-Particle Duality”
Photons
Photons are the smallest quanta of light. The energy of the photon is propor-tional to frequency (or inversely proportional to wavelength). A large group ofphotons together (collectively) act as a wave.
Energy
Frequency
∝
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 8
Light
Spectrum
Radio Waves
are the same as light - the lowest frequency (longest wave-
length) part of the spectrum. We (humans) cannot sense radio waves. Infrared Radiation
has frequencies less than that of visible light (longer
wavelengths). We cannot see infrared radiation, but we can feel intense infra-red radiation as heat. Visible Light
is a small portion of the spectrum from 400 nm (red) to 700 nm
(violet). Remember, 1 nm = 1x
m. We (humans) see light.
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 10
Light
Interaction with Matter
There are four basic ways in which light can interact with matter: 1. Emission2. Absorption3. Transmission4. Reflection
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 11
Light: Emission
ALL OBJECTS EMIT LIGHT!
The emitted light generally covers a large range in the spectrum.The peak in the spectrum is proportional to the temperature.
λ
peak
×^ T
Knm o (
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 13
Light: Emission
ALL OBJECTS EMIT LIGHT!
The total amount of energy is proportional to the temperature to the forthpower times the size of the object..
RadiatedEnergy
AreaOfObject
σ
T
σ
Watt m
K
o
×
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 14
Light: Emission
What is the spectral peak of light emitted from our body?What is the spectral peak of light emitted from the sun? Important Point: We can tell how hot stars are from their color.
λ
peak
×^ T
Knm o (
λ
peak
×
K
o
Knm o (
λ
peak
nm
(Infared)
λ
peak
×
K
o
Knm o (
λ
peak
500
nm
(Yellow)
=
ASTR1030 - FALL, 2008. LECTURE 11; PAGE 16
Light: Absorption/Transmission
Every substance has a distinct absorption pattern or finger print.
Important Point: We can tell what a gas is made of by analyzing the
absorption spectrum.
Magnified View
tar
Cloud