>> How hot do they have to be? Where's the line drawn between hot enough to >> flouresce gas and not hot enough. B5?, B3? Between B1 and B2. See the discussion and Hallas color photo at the NGC/IC Web site: http://ngcic.com/MilkyWay/default.htm ...where the naked-eye stars in upper Scorpius serve to show the effect very clearly. \Brian --- This message is from the AZ-Observing mailing list. If you wish to be removed from this list, send E-mail to: AZ-Observing-request@xxxxxxxxxxxxx, with the subject: unsubscribe. The list's archive is at: //www.freelists.org/archives/az-observing This is a discussion list. Please send personal inquiries directly to the message author. In other words, do not use "reply" for personal messages. Thanks.