Starry monday at otterbein
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Welcome to. Starry Monday at Otterbein. Astronomy Lecture Series -every first Monday of the month- April 4, 2005 Dr. Uwe Trittmann. Today’s Topics. Spectra – Fingerprints of the Elements The Night Sky in March. Feedback!.

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Starry Monday at Otterbein

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Starry monday at otterbein

Welcome to

Starry Monday at Otterbein

Astronomy Lecture Series

-every first Monday of the month-

April 4, 2005

Dr. Uwe Trittmann


Today s topics

Today’s Topics

  • Spectra – Fingerprints of the Elements

  • The Night Sky in March


Feedback

Feedback!

  • Please write down suggestions/your interests on the note pads provided

  • If you would like to hear from us, please leave your email / address

  • To learn more about astronomy and physics at Otterbein, please visit

    • http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)

    • http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)


Light and spectra

Light and Spectra

  • Color of light determined by its wavelength

  • White (visible) light is a mixture of all colors

  • Can separate individual colors with a prism


Light is an electromagnetic wave

Light is an electromagnetic Wave

  • Medium = electric and magnetic field

  • Speed = 3 105 km/sec


Electromagnetic spectrum

Electromagnetic Spectrum


Visible light

Visible Light

400–440 nmViolet

440–480 nmBlue

480–530 nmGreen

530–590 nmYellow

590–630 nmOrange

630–700 nmRed


Three things light tells us

Three Things Light Tells Us

  • Temperature

    • from black body spectrum

  • Chemical composition

    • from spectral lines

  • Radial velocity

    • from Doppler shift


Black body spectrum gives away the temperature

Peak frequency

Black Body Spectrum (gives away the temperature)

  • All objects - even you - emit radiation of all frequencies, but with different intensities


Starry monday at otterbein

Cool, invisible galactic gas

(60 K, mostly low radio frequency)

Dim, young star

(600K, mostly infrared)

The Sun’s surface

(6000K, mostly visible)

Hot stars in Omega Centauri

(60,000K, mostly ultraviolet)

The hotter the object, the higher the peak frequency!


Wien s law

Wien’s Law

  • The peak of the intensity curve will move with temperature, this is Wien’s law:

    Temperature / frequency = constant

    So: the higher the temperature T, the smaller the frequency f, i.e. the higher the energy of the electromagnetic wave


Measuring temperatures

Measuring Temperatures

  • Find maximal intensity

     Temperature (Wien’s law)

Identify spectral lines of ionized elements

 Temperature


Spectral lines fingerprints of the elements

Spectral Lines – Fingerprints of the Elements

  • Can use this to identify elements on distant objects!

  • Different elements yield different emission spectra


Origin of spectral lines

Origin of Spectral Lines

  • Atoms:electrons orbiting nuclei

  • Chemistry deals only with electron orbits (electron exchange glues atoms together to from molecules)

  • Nuclear power comes from the nucleus

  • Nuclei are very small

    • If electrons would orbit the statehouse on I-270, the nucleus would be a soccer ball in Gov. Bob Taft’s office

    • Nuclei: made out of protons (el. positive) and neutrons (neutral)


Starry monday at otterbein

  • The energy of the electron depends on orbit

  • When an electron jumps from one orbital to another, it emits (emission line) or absorbs (absorption line) a photon of a certain energy

  • The frequency of emitted or absorbed photon is related to its energy

    E = h f

    (h is called Planck’s constant, f is frequency)


Origin of spectral lines emission

Origin of Spectral Lines: Emission

Heated Gas emits light at specific frequencies

 “the positive fingerprints of the elements”


Origin of spectral lines absorption

Origin of Spectral Lines: Absorption

Cool gas absorbs light at specific frequencies

 “the negative fingerprints of the elements”


Spectral lines

Spectral Lines

  • Light of a low density hot gas consists of a series of discrete bright emission lines: the positive “fingerprints” of its chemical elements!

  • A cool, thin gas absorbs certain wavelengths from a continuous spectrum dark absorption ( “Fraunhofer”) lines in continuous spectrum: negative “fingerprints” of its chemical elements, precisely at the same wavelengths as emission lines.


Doppler shift

Doppler Shift


Application separate close binary stars

Application: Separate close Binary Stars

  • Too distant to resolve the individual stars

  • Can be viewed indirectly by observing the back-and-forth Doppler shifts of their spectral lines


Application classification of the stars

Application:Classification of the Stars

Class TemperatureColorExamples

O30,000 Kblue

B20,000 KbluishRigel

A10,000 KwhiteVega, Sirius

F8,000 KwhiteCanopus

G6,000 KyellowSun,  Centauri

K4,000 KorangeArcturus

M3,000 KredBetelgeuse

Mnemotechnique: Oh, Be AFine Girl/Guy, Kiss Me


The hertzprung russell diagram

The Hertzprung-Russell Diagram

  • A plot of absolute luminosity (vertical scale) against spectral type or temperature (horizontal scale)

  • Most stars (90%) lie in a band known as the Main Sequence


Hertzsprung russell diagrams

Hertzsprung-Russell diagrams

… of the closest stars…of the brightest stars


Stellar lifetimes

Stellar Lifetimes

  • From the luminosity, we can determine the rate of energy release, and thus rate of fuel consumption

  • Given the mass (amount of fuel to burn) we can obtain the lifetime

  • Large hot blue stars: ~ 20 million years

  • The Sun: 10 billion years

  • Small cool red dwarfs: trillions of years

    The hotter, the shorter the life!


The night sky in march

The Night Sky in March

  • The sun is getting higher -> shorter nights!

  • Spring constellations (Cancer,Leo,Coma,Virgo,…) contain few bright stars but many galaxies

  • Jupiter is in opposition this month (i.e. at its brightest)


Moon phases

Moon Phases

  • Today (Waning crescent, 20%)

  • 4 / 8 (New Moon)

  • 4 / 16 (First Quarter Moon)

  • 4 / 24 (Full Moon)

  • 5 / 1 (Last Quarter Moon)


Today at noon

Today at Noon

  • Sun at meridian, i.e. exactly south


10 pm

10 PM

Typical observing hour, early March

  • no Moon

  • Jupiter

  • Saturn at meridian


South east

South-East

Perseus and

Auriga

with Plejades and the Double Cluster


Zenith

Zenith

  • Big Dipper points to the north pole


South west

South-West

  • The Winter Constellations

    • Orion

    • Taurus

    • Canis Major

    • Gemini

    • Canis Minor


South

South

Spring Constellations

- Cancer

- Leo

- Hydra

Deep Sky Objects:

- Beehive Cluster (M44)


Mark your calendars

Mark your Calendars!

  • Next Starry Monday at Otterbein: May 2, 2005, 7 pm

    (this is a Monday )

  • Web pages:

    • http://www.otterbein.edu/dept/PHYS/weitkamp.asp (Obs.)

    • http://www.otterbein.edu/dept/PHYS/ (Physics Dept.)


Mark your calendars ii

Mark your Calendars II

  • Physics Coffee is every Wednesday, 3:30 pm

  • Open to the public, everyone welcome!

  • Location: across the hall, Science 256

  • Free coffee, cookies, etc.

  • Details about Otterbein’s Rocket Contest there!


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