Transcript Object A

Astronomy 1020-H
Stellar Astronomy
Spring_2016
Day-15
Course Announcements
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1st “Hot Topics in Science”: Coming soon …
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Topics this semester are: Human Cloning, Environmental
Toxicology, & Fracking … includes pizza.
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Dark Night Observing: Mon. 2/29 & Wed. 3/2 –
7:30pm at the APSU Observatory
Exam-2 – Fri. 3/4 Chapters 5 & 6
Smartworks Chapters 5 & 6: Due Fri. 3/4
Spring Break Mar. 5-13 (Sat.-Sun.)
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APSU Research and Creativity Forum April 15, 2016
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Abstracts are due: 4:00pm Fri., March 18
Feb. 29 – Last day to drop with an automatic “W”
Apr. 1 – Last day to drop a class with W, F, FA
 The motion of a light source toward or away
from us changes our perception of the
wavelength of the waves reaching us.
 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.
 Temperature is a measure of the average
speed of the motions of atoms.
 Kelvin scale: Water freezes/boils at 273 K /
373 K.
 Absolute zero is when thermal motion stops.
Emitted Light
 Luminosity: amount of light leaving a
source.
 The amount and type of light leaving a
source changes as an object heats up or
cools down.
 The hotter an object is, the more luminous
it is.
 The hotter an object is, the bluer it is.
 Dense objects emit
a blackbody (or
Planck) spectrum.
 Continuous.
 Gives light at all
wavelengths.
 Example:
incandescent light
bulb.
 For two objects of
the same size, the
hotter one will:
• Emit more total light
at all wavelengths.
• Emit more total
energy every
second.
• Emit light at shorter
wavelengths, on
average.
Stefan’s Law
 Flux is the total amount of energy emitted
per square meter every second (the
luminosity per area).
 Then:
F  T
4
where T is the temperature, F is the flux,
and  (sigma) is called the StefanBoltzmann constant.
 Hotter objects emit much more energy (per
square meter per second) than cool objects.
Wien’s Law
 The peak wavelength of a blackbody is
inversely proportional to its temperature.
2
,
900
,
000
nm
K


peak
T
 Peak wavelength peak : the wavelength of
light of a blackbody that is emitted the
most.
 Here the wavelength is in nanometers and
the temperature is in kelvin.
 “Hotter means bluer.”
MATH TOOLS 5.3
 With the Stefan-Boltzmann law, you can find
Earth’s flux using its average temperature of
288 K.
 Using Wien’s law, you can find the Sun’s
surface temperature using the fact that its
peak wavelength is around 500 nm.
Luminosity is the total energy (light)
emitted by an object in each second.
 Stefan-Boltzmann law
 Luminosity depends on an surface area (A),
4
and its temperature (T ); Surface Area ∝ R
 Luminosity = 4π R  T
2
2
4
 Big and Hot objects have greater luminosity than small
cool objects
Great Blizzard of 2015 – Part 3
Exam Sadistics
Metric
Number
Mean
StdDev
Median
Mode
High
Low
Ex-1
28/32
70.7
15.3
73.2
--95.2
40
How BIG Are the Stars?
While We Wait for Everyone
Luminosity is the total energy (light)
emitted by an object in each second.
 Stefan-Boltzmann law
 Luminosity depends on an surface area (A),
4
and its temperature (T ); Surface Area ∝ R
 Luminosity = 4π R  T
2
2
4
 Big and Hot objects have greater luminosity than small
cool objects
Lecture Tutorial
Luminosity: (pg 55)
 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.
Hertzsprung-Russell Diagram
Luminosity (solar units)
10,000
1
4
1,000
100
10
3
1
0.1
0.01
2
5
0.001
0.0001
20,000
10,000
Temperature (K)
5,000
Which star is Hot and Dim?
Luminosity (solar units)
10,000
1
4
1,000
100
10
3
1
0.1
0.01
2
5
0.001
Temperature (K)
0.0001
20,000
10,000
Temperature
(K)
5,000
Which star is Cool and Dim?
Luminosity (solar units)
10,000
1
4
1,000
100
10
3
1
0.1
0.01
5
0.001
2
Temperature (K)
0.0001
20,000
10,000
Temperature (K)
5,000
Which star is Largest?
Luminosity (solar units)
10,000
1
4
1,000
100
10
3
1
0.1
0.01
2
5
0.001
0.0001
20,000
10,000
Temperature (K)
5,000
Which star is smallest?
Luminosity (solar units)
10,000
1
4
1,000
100
10
3
1
0.1
0.01
5
0.001
Temperature (K)
0.0001
20,000
10,000
Temperature (K)
5,000
2
L
B
2
4r
 Brightness is the
amount of light
arriving at a
particular place.
 Decreases as the
distance from a light
source increases,
obeying an inverse
square law.
 The light spreads
out over a greater
area.
Lecture - Tutorial:
Blackbody Radiation (pg. 59)
 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.
Star A
Star A
Star A
Star D
Energy
Star C
Output per
second
Star B
VIBGYOR
VIBGYOR
Wavelength
VIBGYOR
Which has the longer peak wavelength?
1.
Star A
2.
Star C
Star A
Energy
Output
per
3.
Same
Star C
second
VIBGYOR
Wavelength
Which has the lower surface
temperature?
1.
Star A
2.
Star C
Star A
Energy
Output
per
3.
Same
Star C
second
VIBGYOR
Wavelength
Which star looks red?
1.
Star A
Star A
Energy
2.
Star C
3.
Both
4.
Neither
Output
per
Star C
second
VIBGYOR
Wavelength
Which has the greater energy output?
1.
Star A
2.
Star C
Star A
Energy
Output
per
3.
Same
Star C
second
VIBGYOR
Wavelength
Which star is larger?
1.
Star A
2.
Star C
Star A
Energy
Output
per
3.
Same
Star C
second
VIBGYOR
Wavelength
Which star is larger?
1.
Star A
2.
Star D
3.
Same
Star A
Star D
Energy
Output
per
second
VIBGYOR
Wavelength
Try to determine EVERYTHING about how these four
stars compare!! Temp, Energy output, color, size
(area)…..
Object
A
Energy Output per second
VIBGYOR
range
Object C
Wavelength
visible
range
Object
B
Wavelength
visible
VIBGYOR
Energy Output per second
range
VIBGYOR
Energy Output per second
Energy Output per second
visible
Wavelength
visible
range
Object D
VIBGYOR
Wavelength
 The telescope is the
astronomer’s most
important tool.
 Purpose: to gather
light of all kinds.
 Two kinds of optical
telescopes:
reflecting and
refracting.
 Invented in 1608 by
Hans Lippershey.
Telescopes

Telescopes have three functions:
1.
Gather light

2.
Resolve objects

3.
LGP ∝ Area = πR2
Θ = 2.06 X 105 (λ/D)
Magnify EXTENDED objects
CONNECTIONS 6.1
 When light encounters a new material, it can
either experience reflection or refraction.
 In refraction, the light will be bent depending
on the value of the index of refraction
relative to the first material.
CONNECTIONS 6.1
 Refraction depends on the wavelength—
violet light is bent more than red.
 Dispersion: the resulting spreading out of
the wavelengths of light.
 Causes chromatic aberration in lenses,
which can be fixed by a compound lens.
 Refracting telescopes
use lenses.
 Objective lens: refracts
the light.
 Aperture: size of the
objective lens (larger
aperture gathers more
light).
 The objective lens is
placed in the aperture.
 Focal length: distance between lens and the
image (longer = larger image).
 Aperture sets the light-collecting power.
 Focal length determines the image size.
 The largest refracting telescope has a
1-meter aperture.
 Problems with refractors:
• Need to be large to have a long focal length.
• Lenses suffer from chromatic aberration.
 Reflecting telescopes use mirrors.
 There are primary and secondary mirrors.
 Focal length is determined by the path the
light takes reflecting off the mirrors.
 Reflectors have
advantages over
refractors.
 No chromatic aberration.
 Bigger telescopes due to
increased focal length in
the same amount of
physical space and no
need for massive lenses.
 The largest telescopes in
the world are reflectors.
A concave mirror focuses light
Spherical Aberration
Correcting S.A.
Spherical
aberration can
be eliminated by
a parabolic
shape or a
corrector plate
Focal Arrangements
There are
several
types of
reflecting
telescopes
Schmidt-Cassegrain
MATH TOOLS 6.1
 The light-gathering power of a telescope is
proportional to the square of the aperture
size.
 A telescope’s magnification depends on the
focal lengths of the objective lens or mirror
and the eyepiece.