Lecture 13: Searching for planets orbiting other stars I: Properties of Light

1. Lecture 13: Searching for planets orbiting other stars I: Properties of Light How could we study distant habitats remotely ? The nature of light - spectrum, spectral lines Using spectroscopy to do remote sensing of exoplanets

2. NASA Messenger space probe enters into orbit around Mercury

3. The nature of light • Light - electromagnetic waves that have: Wavelength Frequency Speed … and Energy

4. Direct Detection of Planets • Direct detection is challenging because of the technical limits of telescopic observations

5. Telescopes: 2 basic designs • Telescopes with a lens for an objective are refractors:

6. Telescopes: 2 basic designs • All large telescopes are reflectors: with a mirror, instead of a lens.

7. Telescopes • Harvard is a partner in the construction of the largest new telescope: The Giant Magellan Telescope (D ~ 25 m)

8. Light and Telescopes - Optics • Resolution - the ultimate limitation comes from the wave properties of light: diffraction

9. Light and Telescopes - Optics • Resolution - the ultimate limitation comes from the wave properties of light: diffraction

10. Light and Telescopes - Optics • Resolution - the ultimate limitation comes from the wave properties of light: diffraction

11. Telescopes: 2 basic designs • All large telescopes are reflectors: with a mirror, instead of a lens.

12. Light and Telescopes - Optics • Resolution and telescope spider diffraction

13. Light and Telescopes - Optics • Resolution and telescope spider diffraction

14. Telescopes: 2 basic designs • Telescopes with a lens for an objective are refractors: suffer from chromatic aberration

15. The nature of visible light White light is a mixture of the colors; monochrome light behaves like waves of the same wavelength.

16. The nature of visible light • Visible light: a form of electromagnetic energy / radiation that our eyes are sensitive to.

17. The Spectrum • Can tell us temperature: • a thermal radiation spectrum is a continuous spectrum of light that depends only on the temperature of the object that emits it.

18. The Spectrum • Thermal spectrum: • the spectrum of the Sun is roughly similar to a thermal spectrum.

19. The Spectra of Stars • The Sun vs. a smaller, cooler star (M-star), • The wavelength at which a star’s spectrum peaks, reveals the star’s surface temperature:

20. Using Spectra for Remote Sensing • Forming spectral lines in the spectrum

21. Using Spectra for Remote Sensing • Measuring spectral lines in the spectrum

22. Electron Orbits in Atoms

23. Electron Orbits in Atoms Plots of electron density shapes of 1s, 2p and 3d orbitals:

24. Atoms and Spectral Lines • Spectral lines correspond to the energy of a transition an electron makes between two distinct states.

25. Model: Seager & Sasselov 2000 Detection: Charbonneau et al 2002

26. Molecules and Spectral Lines • Spectral lines of molecules also correspond to the energy to transit between distinct states

27. The Spectra of Stars • The Sun vs. a smaller, cooler star (M-star)

28. The Spectra of Planets • Mars

29. Using Spectra for Remote Sensing • Forming spectral lines in the spectrum

31. Main points to take home: • Visible light: form of electromagnetic energy (radiation) to which our eyes are sensitive. • Spectrum: the amount of light of any given wavelength, emitted or reflected by an object. • Thermal spectrum: a simple spectrum that depends only on the object’s temperature. • Spectral lines: in emission or absorption; every atom and molecule has a specific set.