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

So for same bulb

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 EquationOne of these items is the light bulbOne of these items is the SunL is the power

For same fluxiness

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)

% difference• Used when you don’t know the answer.

Provides a measure of the precision of your results.

• Helps identify outliers.

Accuracy & Precision

Wien’s Law – Color and Temperature

Wavelength in meters from this formula1 nanometer = 10-9 meter1 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/

Wavelengths_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

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 X-ray 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/

black_holes/

Black Hole• G1915

+105. 14 solar masses.

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.cosmic-ray.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/

filters.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