Posted by Robin Leadbeater at 19:32 on 2014 Jan 27
Hi David,Type 1a are indeed the standard candle but you need to take into account the extinction due to everything between it and us. This is done in various ways eg by measuring the amount the spectrum is reddened (The spectrum should get brighter towards the blue but here has a downward slope towards the red) or by measuring the strength of the absorption lines from the interstellar material like the Na D lines here. There is an impressive (to me at least!) early analysis of these in http://www.astronomerstelegram.org/?read=5797 CheersRobin