1. Oct. 16, 2007 1 Review: Continuum vs. Line spectra of Stars Blackbody continuum spectrum (Wien’s Law and S-B Law) give color and thus temperature, and luminosity (respectively) of stars Each element (H…. Fe… U) has unique spectral lines since electron orbits differ since total electron number differs Light from the stars (Sun, Vega, etc.) show spectral lines primarily in absorption (dark lines) due to light from “hot” surface (BB continuum) shining up through “cooler” overlying stellar atmosphere. Total spectrum of a star is then underlying BB continuum with absorption lines “carved out” of the continuum (and for very hot stars, or coronae of cool stars, emission lines are seen)

2. Oct. 16, 2007 2 Line spectra allow measure of Velocities Having “sharp” wavelength (color) signatures in spectral lines (usually absorption lines) allows stellar velocity to be measured by Doppler Shift: –Wavelength “compressed” (blueshift) vs. “stretched” (redshift) by amount Δλ/λ o = v/c, for source moving away/toward us at velocity V and line at rest wavelength λ o Primary tool of locating stars in their orbits about our Galaxy (all stars in orbit about galactic center; so all moving via Kepler’s Laws but with differing radial velocities with respect to Sun. Enables measurement of rotation velocity of stars (e.g. Sun) – DL3!

3. Oct. 16, 2007 3 Introduction to Telescopes – what for? Light (over all EM spectrum) from stars is faint; needs to be first collected (with large lens or mirror) and then imaged (so precise direction of light, and star to star details, preserved). See Tf6-3 An refracting optical Telescope employs a collecting lens or (objective) and eyepiece or camera focusing lens (Tf6-5) to “grab” as much light as falls on Objective and focus to image A reflecting optical Telescope employs a primary mirror (instead of lens) which reflects to a secondary mirror and then to a focus (for eyepiece or a camera). The Clay telescope is a Cassegrain focus (Tf6-11) with primary mirror aperture 16in = 0.4m

4. Oct. 16, 2007 4 Telescopes across the EM spectrum… Radio telescopes (e.g. Tf6-22f for Parkes) are huge: their surface need not be as accurate as for an optical telescope, since wavelength so much longer. Mirror surfaces usually “figured” (smooth) to λ/10 IR telescope (e.g. Tf6-26 for Spitzer) are generally smaller since their mirrors need to be cooled to reduce background (at long IR wavelengths; not needed at visible-IR wavelengths) X-ray telescope (e.g. Tf-30 for Chandra) must employ grazing incidence or very shallow angles of reflection: very small collecting area for given diameter mirror – see blackboard notes. Gamma-ray telescopes don’t reflect at all; particle nature of photons instead employed to image – see blackboard notes…