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Fingerprints in Fingerprints in SunlightSunlight

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How can we How can we study the stars study the stars & Sun?& Sun?

We can’t get there from hereWe can’t get there from here Only/primary way of learning about distant Only/primary way of learning about distant

objects is through their light (electromagnetic objects is through their light (electromagnetic spectrum)spectrum)

Light has ‘fingerprints” which provide Light has ‘fingerprints” which provide information about itinformation about it

How can we “read” these fingerprints and How can we “read” these fingerprints and what do they tell us about the star?what do they tell us about the star?

No matter how good your No matter how good your telescope, a star is only a telescope, a star is only a point of lightpoint of light

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What is the What is the spectrum of spectrum of light?light?

Anything hotter than absolute zero Anything hotter than absolute zero radiates/emits energy, i.e. lightradiates/emits energy, i.e. light

Sun & stars emit a continuous spectrum Sun & stars emit a continuous spectrum (“black body”) of EM radiation(“black body”) of EM radiation

Our eyes see “white” light, which is Our eyes see “white” light, which is made of a spectrum of colors, visible in made of a spectrum of colors, visible in a rainbowa rainbow

Spectrum = “The distribution of energy Spectrum = “The distribution of energy emitted by a radiant source, e.g. the emitted by a radiant source, e.g. the Sun, arranged in order of wavelengths”Sun, arranged in order of wavelengths”

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What is a What is a spectrograph?spectrograph?

A relatively simple-to-A relatively simple-to-understand scientific understand scientific instrument to look at instrument to look at a spectruma spectrum

Like a prism – breaks Like a prism – breaks light into its colorslight into its colors

Thin, rectangular slit Thin, rectangular slit produces a rectangle produces a rectangle of lightof light

Example output from a spectrograph

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Your Simple Your Simple SpectrographSpectrograph

Diffraction gratingDiffraction grating

(similar effect to prism(similar effect to prism

or CD)or CD) Slit & light sourceSlit & light source Scale (optional)Scale (optional) Eye or instrument Eye or instrument

for viewingfor viewingBuild, examine &

try out your spectrograph

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Most astronomy is Most astronomy is done with done with spectrographs!spectrographs!

Your spectrograph Stanford Solar Center Home-made

spectrograph attached to telescope

NASA’s SOHO Spacecraft

Hubble’s new Cosmic Origins Spectrograph

Student spectrograph & gas

lamp

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What can we learn with What can we learn with a spectrograph?a spectrograph?

Sometimes there are extra bright Sometimes there are extra bright colorscolors

Sometimes there are missing Sometimes there are missing colorscolors

To infraredTo ultraviolet

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Fingerprints in LightFingerprints in Light

The extra or missing colors indicate certain The extra or missing colors indicate certain chemical elements have affected the lightchemical elements have affected the light

Each chemical element changes the spectrum Each chemical element changes the spectrum either by making certain colors brighter or either by making certain colors brighter or removing certain colorsremoving certain colors

Each chemical element has a different and Each chemical element has a different and unique pattern of colors, hence the unique pattern of colors, hence the “fingerprints”“fingerprints”

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Example fingerprintsExample fingerprints

HydrogenHydrogen

HeliumHelium

SodiumSodium

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Some Elements on the Some Elements on the SunSun Hydrogen (H)Hydrogen (H)

Helium (He)Helium (He)

Sodium (Na)Sodium (Na)

Oxygen (OOxygen (O2)2)

Iron (Fe)Iron (Fe)

Sun

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What does it mean What does it mean “lines”?“lines”?

We call these chemical fingerprints “lines”, We call these chemical fingerprints “lines”, because they show up in our spectrograph because they show up in our spectrograph as thin rectangles, from our rectangular slitas thin rectangles, from our rectangular slit

Absorption lines – produced when a Absorption lines – produced when a chemical element has absorbed energy chemical element has absorbed energy

Emission lines – produced when a chemical Emission lines – produced when a chemical element has emitted energyelement has emitted energy

Lines can show up in any part of the EM Lines can show up in any part of the EM spectrum (not just visible light)spectrum (not just visible light)

Hydrogen lines

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Let’s try an exampleLet’s try an example

Point your Point your spectrograph to an spectrograph to an incandescent light incandescent light or sunlightor sunlight

Next, point your Next, point your spectrograph to a spectrograph to a fluorescent light fluorescent light bulbbulb

What do you see? What do you see? Especially notice the Especially notice the bright green linebright green line

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You should have seen a You should have seen a continuous spectrum with continuous spectrum with some extra bright colored some extra bright colored lineslines

Fluorescent bulb, Fluorescent bulb, old styleold style

Fluorescent bulb, Fluorescent bulb, new stylenew style

MercuryMercury

What do you What do you conclude?conclude?

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Another experimentAnother experiment

Work in teamsWork in teams Take your candleTake your candle Burn a hollow around your wickBurn a hollow around your wick Put salt in the hollow, or pour Put salt in the hollow, or pour

salt onto the flamesalt onto the flame Look for a brief flashLook for a brief flash What do you see?What do you see?

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What did you see?What did you see?

The candleThe candle

Sodium spectrumSodium spectrum

What is salt? What is salt? Sodium chlorideSodium chloride

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Is there sodium on the Is there sodium on the Sun?Sun?

Solar spectrumSolar spectrum

Sodium spectrumSodium spectrum

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How does How does this work?this work?

Atoms are a nucleus surrounded by shells Atoms are a nucleus surrounded by shells or “energy levels” of electronsor “energy levels” of electrons

Different chemical elements have Different chemical elements have different levels where electrons can livedifferent levels where electrons can live

Electrons can be knocked up levels, or Electrons can be knocked up levels, or down levelsdown levels

Electrons can be knocked off completely Electrons can be knocked off completely (atom becomes ionized)(atom becomes ionized)

Lost electrons can be recapturedLost electrons can be recapturedInstructor will demonstrate the Nested Globe Atom model

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Energy LevelsEnergy Levels

To move from one level or To move from one level or another requires another requires ENERGYENERGY

Movement from one specific Movement from one specific energy level to another requires energy level to another requires a specific amount of energya specific amount of energy

Higher levels require more Higher levels require more energyenergy

Energy is conserved, never lostEnergy is conserved, never lost

Each element requires different sets or Each element requires different sets or collections of these “amounts of collections of these “amounts of energy”energy”

Energy absorbed – electron jumps up

Energy released – electron jumps down

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PhotonsPhotons

An “amount of energy” is An “amount of energy” is essentially a photon, or a essentially a photon, or a packet of lightpacket of light

Photons come in only Photons come in only certain “sizes”, or certain “sizes”, or amounts of energyamounts of energy

Light then consist of Light then consist of little photons, or little photons, or quantaquanta, , each with an energy of each with an energy of Planck's constant times Planck's constant times its frequency.its frequency.

Planck's constant = 6.626068 × 10Planck's constant = 6.626068 × 10-34-34 m m22 kg / skg / s

2020

Hydrogen,Hydrogen, an example an example

Hydrogen has 1 electronHydrogen has 1 electron

From it’s resting state, From it’s resting state, Level 1, this electron can Level 1, this electron can move to a number of move to a number of other levels, e.g. Level 2, other levels, e.g. Level 2, Level 4, Level “n”Level 4, Level “n”

The energy required to The energy required to move between any 2 move between any 2 levels is specific for levels is specific for hydrogen & for each hydrogen & for each chemical elementchemical element

Level 1 to level 2absorbs a 122 nm photon of energyfrom “outside”

Level 2 to level 1emits a 122 nm photon of energy

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Hydrogen, Hydrogen, stillstill

Electrons can skip Electrons can skip levels, up or downlevels, up or down

Some skips Some skips to/from certain to/from certain levels have nameslevels have names

For example, the For example, the hydrogen Balmer hydrogen Balmer Series – any skips Series – any skips that start or end that start or end at Level 2at Level 2

Balmer Series, any skips that originateor end at Level 2

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Why is the Balmer Why is the Balmer Series interesting?Series interesting?

Luckily for us, the Luckily for us, the skips to and from skips to and from Level 2 in hydrogen Level 2 in hydrogen emit or absorb emit or absorb photons of photons of visible visible light!light!

But other skips can result in UV, But other skips can result in UV, infrared, or other EM infrared, or other EM spectrum photos.spectrum photos.

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Prepare for an activityPrepare for an activity

Make sure everyone receives a Make sure everyone receives a Spectra WorksheetSpectra Worksheet

Make sure everyone receives a kit Make sure everyone receives a kit of straws, skewers, and styrofoam of straws, skewers, and styrofoam balls.balls.

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Let’s PlayLet’s Play

6 -> 2

5 -> 2

4 -> 2

3 -> 2

Lower energy -><- Higher energy

Take out your straws, styrofoam balls, sticks, and spectra sheet

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Questions on any of Questions on any of these concepts?these concepts?

Next I’ll quickly explain what is an Next I’ll quickly explain what is an H-alpha solar telescope. These H-alpha solar telescope. These are the most common form of are the most common form of amateur solar telescopes.amateur solar telescopes.

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H alphaH alpha

H alphaH alpha is the name of is the name of the transition ofthe transition of

electrons in hydrogen electrons in hydrogen between Levels 2 and 3between Levels 2 and 3

(656 nm). (656 nm). i.e. your red i.e. your red (pink) straw(pink) straw

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The Sun “in H alpha”The Sun “in H alpha”

Hydrogen alpha filters allow only light in the 656nm wavelength to pass through. This is the line that appears in the red part of the spectrum when an electron moves from Level 3 to Level 2.

This allows us to see light produced at a particular temperature in the photosphere (surface) of the Sun.

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Questions on H-alpha Questions on H-alpha solar telescopes?solar telescopes?

After the presentation, we will view the Sun through an h-alpha telescope.

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Absorption & EmissionAbsorption & Emission

3030

Absorption and Absorption and Emission on the SunEmission on the Sun

The Sun emits a continuous The Sun emits a continuous spectrumspectrum

All light from the Sun comes All light from the Sun comes from the surface, or from the surface, or photosphere, 5800 degrees Kphotosphere, 5800 degrees K

As the atoms bounce around the As the atoms bounce around the photosphere, photons are photosphere, photons are constantly being absorbed and constantly being absorbed and re-emittedre-emitted

Although the original light was Although the original light was traveling our way, re-emitted traveling our way, re-emitted photons are sent off in all photons are sent off in all directions so most of them never directions so most of them never make it to our instrumentsmake it to our instruments

The result is a continuous The result is a continuous spectrum with absorption linesspectrum with absorption lines

A high resolution really long spectrum, chopped into

lines sliced and stacked on top of each other

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Absorption in the solar Absorption in the solar spectrumspectrum

Solar surface

Photons->

H

He

O2

Fe

H

Photons are constantly being absorbed and re-

edmitted in random directions

Fewer of the absorbed and re-edmitted photos end up

traveling toward us

Questions?

3232

What secrets do What secrets do spectra tell us?spectra tell us? TemperatureTemperature CompositionComposition MovementMovement Magnetic fieldsMagnetic fields

3333

Reading a spectrumReading a spectrum

A spectrum can be graphed as wavelength vs. intensity

6169 6172 6175 6178

Measure Here

Location and shape changes of the line give us a lot of additional information

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Spectra tell us Spectra tell us temperaturestemperatures

If you look at the If you look at the strongest colors or strongest colors or wavelength of light wavelength of light emitted by a star, then emitted by a star, then you can calculate its you can calculate its temperature temperature

temperature in degrees Kelvin = temperature in degrees Kelvin =

3 x 103 x 1066/ wavelength in nanometers = 5800 K on the surface of our / wavelength in nanometers = 5800 K on the surface of our SunSun

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Spectra tell us about Spectra tell us about compositioncomposition Am emission or absorption line Am emission or absorption line

means a specific chemical means a specific chemical element has been involved with element has been involved with the light you are seeingthe light you are seeing

Careful, though. The element Careful, though. The element could be from the source, or from could be from the source, or from an intervening plasma or gas an intervening plasma or gas cloudcloud

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How do spectra tell us How do spectra tell us about movement?about movement? A Doppler shift happens when an object is moving A Doppler shift happens when an object is moving

towards or away from us, as in a siren coming towards towards or away from us, as in a siren coming towards usus

Wavelength is influenced by the movementWavelength is influenced by the movement It works with sound, with light, with any waveIt works with sound, with light, with any wave

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Spectral line in Labis at 643.6 nm

Spectral line shifted to666.4 nm in source.

Speed of source = 300,000 x (666.4 – 643.6)/643.6 = +10,628 km/s

Hydrogen spectrumin lab

Hydrogen spectrum ina distant moving object

Doppler Shifts tell us Doppler Shifts tell us about motionsabout motions

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Doppler, continuedDoppler, continued

Motion away Motion away from us from us results in a results in a “red shift”“red shift”

Motion Motion towards us towards us results in a results in a “blue shift“blue shift

Why don’t they call it a violet shift?

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Spectra tell us about Spectra tell us about magnetismmagnetism

Sunspots are magnetic

storms on the Sun Magnetic fields

cause spectral lines to split into

thirds

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NASA’s Solar Dynamics NASA’s Solar Dynamics Observatory (SDO)Observatory (SDO)

Launched in November 2010Launched in November 2010 3 instruments, one of which is 3 instruments, one of which is

Helioseismic Magnetic Imager (HMI)Helioseismic Magnetic Imager (HMI) HMI is from the Solar Observatories HMI is from the Solar Observatories

team at Stanford – my group!team at Stanford – my group! HMI works similarly to a spectroscopeHMI works similarly to a spectroscope

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SDO and HMISDO and HMI

How SDO looks in space

HMI instrumentSDO before launch

We are excited!!!

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Any Questions?Any Questions?

Use your spectroscopes Use your spectroscopes to look at moonlight, to look at moonlight, reflected sunlight, reflected sunlight, fluorescent lights, neon fluorescent lights, neon signs, mercury vapor signs, mercury vapor and sodium streetlights, and sodium streetlights, etc.etc.

Show people how Show people how science is done by science is done by teaching about the Sun teaching about the Sun and spectroscopyand spectroscopy!!

Thank you!Thank you!Sun Dragon Art image © by Henry Roll. Used with permission.