Paul - Visual binaries are true binary stars whose separations can be observed visually as opposed to spectrographic binaries, which require a spectrometer or interferometer. Optical binaries are the ones that are not true binaries, but only appear to be. Alberio (bet Cyg, WDS 19307+2758, ADS 12540, CCDM19307+2758) shows up as binary in the 6th Catalogue of Orbits of Visual Binary Stars. The cool thing about the 6th Catalogue at - http://ad.usno.navy.mil/wds/orb6/orb6frames.html - are its orbital diagrams, e.g. gam Vir http://ad.usno.navy.mil/wds/orb6/PNG/wds12417-0127r.png Alberio http://ad.usno.navy.mil/wds/orb6/PNG/wds19307+2758k.png - which makes for a good teaching graphic. The diagrams are supposed to launch automatically. On my MS-IE 7.0 browser the javascript is crashing and I have to manually build up the links to retrieve the diagrams. Alberio has an orbital grade of "4" meaning - "Individual elements entitled to little weight,and may be subject to substantial revisions. The quantity 3 log(a) - 2 log(P) should not be grossly erroneous. This class contains: orbits with less than half the ellipse defined; orbits with weak or inconsistent data; orbits showing deteriorating representations of recent data..." - Kurt P.S. - See also Kaler's description stating that the system is a triple, with Alberio A having a companion: http://www.astro.uiuc.edu/~kaler/sow/albireo.html P.P.S. - Looks like I blew the description of basic spectroscopy and Alberio for your prospective student. Hot solid body = continuous spectrum Hot gas = emission spectra Cool gas = absorption spectra _______________________________________________ Sent via CSolutions - http://www.csolutions.net