GEARS Workshop Tuesday
2011
Warm Up
• Good morning!
• Complete form online
• Complete paper evaluation up to activities
completed
• Create a code name to add to top of sheet so
you can get the same one back each day – OR
keep yours safe all week to turn in on Friday.
Flux Simulator
• Flux Simulator for Fluxiness we found
1
Iµ 2
d
constant proportional to power of bulb
I=
2
d
So for same bulb
constant proportional to power of bulb
I1 =
2
d1
constant proportional to power of bulb
I2 =
d22
constant for bulb = I 2 d22 = I1d12
I 2 I1
= 2 when bulb constant
2
d1 d2
Engage: Flux Lab
• How can we use the inverse square law of
light to find out how luminous the sun is?
• Think for a few minutes in groups of 4 or 5.
Brainstorming.
Flux Lab – groups of 3-4
• Demonstrate the concept in the room with 2
light bulbs.
• Explain that there are 2 measurements to
make
– distance to bulb for equal brightness wax – each
person decides
– Color of wax on each side when equal brightness
Photometer Lab Equation
One of these items is the light bulb
One of these items is the Sun
L is the power
L1
L2
=
2
2
(dist1 ) (dist2 )
For same fluxiness
Sun power
Fluxiness seems same =
2
dsun
Bulb power
Fluxiness seems same =
2
dbulb
Sun power Bulb power
=
2
2
dsun
dbulb
Where the d represents distance to the wax from sun or bulb
Discussion
• % error
• Color – each person better have something
written down
• Sources of error: Brainstorm
% error
• Used when know actual value and you are
doing a verification lab.
• Provides a measure of the accuracy of your
results (hint – see characteristics of science)
measured - known
% error =
´100%
known
% difference
• Used when you don’t know the answer.
Provides a measure of the precision of your
results.
• Helps identify outliers.
measured - average
% difference =
´100%
(measured + average) / 2
Accuracy & Precision
Wien’s Law – Color and
Temperature
0.0028978 m K
lmax =
T
Wavelength in meters from this formula
1 nanometer = 10-9 meter
1 meter = 109 nanometer
Find Temperature of the Sun
• You need the radius of sun from the pinhole
camera experiment.
• Prize to the group with the closest
measurement if your workshop facilitator
thinks it is OK
Find color of the Sun
• http://eosweb.larc.nasa.gov/EDDOCS/Wavele
ngths_for_Colors.html
• Compare with what you saw.
Explain: Flux Lab
• We used inverse square law model & known source
• We assumed Sun was blackbody (known from other
observations)
• We used Stefan-Boltzmann model and pinhole
camera radius (from geometry and knowing
distance) to get temperature of the sun as blackbody
• We used Wien’s Law model for peak wavelength of
blackbody emitter using the temperature
Models
• Models (aka theories, math equations,
previously tested ideas) help extend our
knowledge of the world around us
• Why can’t we just go measure the
temperature of the Sun?
• How do we measure anything in astronomy?
Sun
• Insert advertisement here
– Fall workshop
– Resource Teachers
– GEARS wiki
• Sun & Space Weather Introduction
Elaborate: Intrinsic Properties
of Stars
• Let’s think back to initial categories made of
star image
• Having made a few measurements now – let’s
list the intrinsic properties of stars on the
board together
Organizing Stars
• Astronomers want nothing more than to
classify and categorize – just like every other
scientist
• First thing we do is try to plot things on graphs
to see if there is a pattern
• Let’s plot two intrinsic properties against one
another.
•
•
•
•
This is on board – not in
powerpoint
Start with axes only
Point out logarithmic scaling
Point out backwards temperature
Add main sequence – units of solar lum –
what that mean
• Test for understanding – ask where blue stars
• Ask where red stars
• Ask where luminous, cold, hot, less luminous
•
•
•
•
Add white dwarfs
Ask for understanding – hot cold dim not
Add supergiants
Add giants
• Hey.. You know – dwarfs, giants.. Seems to
imply something about radius
• Blackbodies follow Stefan-Boltzmann relation
• Luminosity and temperature and radius all
related.
Radius on HR diagram
WOW!
• What a great diagram – 3 intrinsic properties
in one graph!
Mass?
• Yes indeedy… mass for main sequence is on
this diagram too.
• Luminosity – Mass Relation
LµM
3.5
Age on diagram?
• Sort of – if high mass main sequence star –
know something. As they fuse such a short
time
• But what about if it is a G star, like the Sun?
• Need groups of stars and use a model
Composition?
• No… but hey
• Luminosity, Mass, temperature, radius, and
age… on one graph!
• Models of blackbodies allow us to know more
about stars than we can get from observations
alone.
•
•
•
•
•
•
•
Elaborate more: Create a
diagram
If time – if not, assign for HW.
Nearby Stars
Bright Stars
Cluster 1
Cluster 2
Put all on same axes!
See today’s online agenda for a data file.
Your Graphs
• Did all the graphs look the same?
Stellar Evolution
• Engage: What are some questions you have
about stars right now?
• Brainstorm a list on your whiteboards.
Explore: Stellar Evolution
• Simulators – as on agenda.
• Is the main sequence for stars on the L-T
diagram a sequence of age?
Explain
• Stars are simply balance (or imbalance) of forces – in
vs. out.
• Formation – gravity stronger than gas pressure force
• Main sequence – gravity in balance with gas pressure
force (btw – fusion!)
• Unbalance signals end of main sequence –exciting
things happen
• Then back in balance for end state
Star Formation
• What are some of the things you notice about
places where we find young stars?
Star Formation
M16 – X-ray stars
Star Formation
• Accompanied by dust!
– Collapse requires cold – think ideal gas law
– “Dust” protects from light from nearby stars that
might heat gas
• Wispy gas – the future fuel for the star
• And some very powerful stars that are very
high temperature – emitting lots of light at Xray and UV- the signatures of young stars
Explain:
• Do all stars evolve the same way?
• Do all stars take the same amount of time to
evolve?
• What is your evidence to support your claim?
Summary:
•
•
•
•
Really high mass
High mass
The Sun and the lower mass stars
http://cheller.phy.georgiasouthern.edu/gears/
Units/2-StellarEvolution/2Stars_7.html
• Compare main sequence lifetimes, end states.
End of Stars
• Main sequence is the stage of existence where
stars are fusing hydrogen to helium
• Spend largest fraction of their existence doing
this
• More massive stars – short lived
• Low mass stars – long lived
• Range – 100,000 years – 100 billion years!
BPPSC – Red Giant – on left.
Artist conception - right
Planetary Nebula
White dwarf –
Artist impression
Supergiant to Supernova
Crab SNR + Pulsar
Black Holes
• http://hubblesite.org/explore_astronomy/blac
k_holes/
Black Hole
• G1915
+105.
14
solar
masse
s.
Patterns + models = stellar
evolution theory
• Along with physical models of gravity, gas
pressure, electrostatic repulsion, nuclear
physics
• Plus some nice spectral line measurements
• Get a beautiful scenario of stellar evolution
• Imagine the Universe powerpoint
Star Lifetimes
• http://astrosun2.astro.cornell.edu/~mcomins/
lab10_solutions.pdf
Cluster ages
• What is a cluster? And why are they
important?
• Globular cluster distribution told us shape of
our own galaxy
• Globular clusters helped us learn about
interstellar “dust”
• Help us determine age of our galaxy
M30 Cluster
Clusters of stars – ages
Which one is younger?
Go back to diagrams made
earlier in XL
• What can those clusters tell you now about
age of the cluster? At least relative ages?
Extra fun question
•
•
•
•
High mass stars fusion Hydrogen to Helium
So do low mass stars
Stars are made up primarily of Hydrogen
So… high mass stars should have lots more
hydrogen to fuse than low mass stars
• How come high mass stars fuse hydrogen for
so much less time?
Misconception alert
• http://aspire.cosmicray.org/labs/star_life/hr_interactive.html
• Comes from images like on next page.
Life after
main
sequence
Evaluate: Can you fill in this
concept map?
• Vocab – Red
Giant, black
hole, white
dwarf,
planetary
nebula,
neutron star,
supernova
Journey to the Stars
• Pairs: One watch and jot down areas in which
students could have misconceptions or in
which a misconception is addressed
• One watch and note some ‘student
worksheet’ ideas.
Extra bonus material
• It seems like temperature measuring is hard –
have to figure out the exact place of the peak
wavelength or know the radius of star
• So is luminosity measuring – adding up all the
light at all wavelengths…
• How do we really measure temperature and
luminosity?
• Magnitude (absolute in a filter, such as U, B, V, R, I, J,
K)
• and ‘color’ which is difference between two
magnitudes (e.g. B-V, U-B, J-K)
• http://astro.unl.edu/naap/blackbody/blackbody.html
• http://astro.unl.edu/naap/blackbody/filters.html
• http://astro.unl.edu/naap/blackbody/animations/filt
ers.html
Outcomes
• Identify end phases of stars like the sun
• Match evolutionary stages to initial mass
ranges
• Relate atmospheric properties to astronomical
equipment needed
• Relate mass of star to lifetime and power
• Correctly identify colors and luminosities of
stars using an HR diagram