Starry Monday at Otterbein

1. Welcome to Starry Monday at Otterbein Astronomy Lecture Series -every first Monday of the month- April 4, 2005 Dr. Uwe Trittmann

2. Today’s Topics • Spectra – Fingerprints of the Elements • The Night Sky in March

3. 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.)

4. 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

5. Light is an electromagnetic Wave • Medium = electric and magnetic field • Speed = 3 105 km/sec

6. Electromagnetic Spectrum

7. Visible Light 400–440 nm Violet 440–480 nm Blue 480–530 nm Green 530–590 nm Yellow 590–630 nm Orange 630–700 nm Red

8. Three Things Light Tells Us • Temperature • from black body spectrum • Chemical composition • from spectral lines • Radial velocity • from Doppler shift

9. Peak frequency Black Body Spectrum (gives away the temperature) • All objects - even you - emit radiation of all frequencies, but with different intensities

10. 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!

11. 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

12. Measuring Temperatures • Find maximal intensity  Temperature (Wien’s law) Identify spectral lines of ionized elements  Temperature

13. Spectral Lines – Fingerprints of the Elements • Can use this to identify elements on distant objects! • Different elements yield different emission spectra

14. 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)

15. 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)

16. Origin of Spectral Lines: Emission Heated Gas emits light at specific frequencies  “the positive fingerprints of the elements”

17. Origin of Spectral Lines: Absorption Cool gas absorbs light at specific frequencies  “the negative fingerprints of the elements”

18. 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.

19. Doppler Shift

20. 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

21. Application:Classification of the Stars Class Temperature Color Examples O 30,000 K blue B 20,000 K bluish Rigel A 10,000 K white Vega, Sirius F 8,000 K white Canopus G 6,000 K yellowSun,  Centauri K 4,000 K orange Arcturus M 3,000 K red Betelgeuse Mnemotechnique: Oh, Be AFine Girl/Guy, Kiss Me

22. 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

23. Hertzsprung-Russell diagrams … of the closest stars …of the brightest stars

24. 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!

25. 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)

26. Moon Phases • Today (Waning crescent, 20%) • 4 / 8 (New Moon) • 4 / 16 (First Quarter Moon) • 4 / 24 (Full Moon) • 5 / 1 (Last Quarter Moon)

27. Today at Noon • Sun at meridian, i.e. exactly south

28. 10 PM Typical observing hour, early March • no Moon • Jupiter • Saturn at meridian

29. South-East Perseus and Auriga with Plejades and the Double Cluster

30. Zenith • Big Dipper points to the north pole

31. South-West • The Winter Constellations • Orion • Taurus • Canis Major • Gemini • Canis Minor

32. South Spring Constellations - Cancer - Leo - Hydra Deep Sky Objects: - Beehive Cluster (M44)

33. 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.)

34. 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!