Re: What does 'RR' stand for in RR Lyrae stars?

Peter,

There are lots of different classes of variable stars, and each class is named after the first object of its type to be discovered. So RR Lyrae stars are named after their prototype, RR Lyrae. Other classes of variable stars include R Coronae Borealis stars, star, AM Herculis stars, and so on.

But how did RR Lyrae get its name? Well, as you may know, 'Lyrae' means that the star is in the constellation Lyra, and the variable stars in each constellation are all named in a specific order. The letters go like this: R, S, T...Z, then RR, RS...RZ, SS, ST..SZ, etc up to ZZ. After ZZ is reached the system continues on with AA, AB, ...AZ, then BB, BC..BZ.. until QZ is reached (but J is omitted because it looks too much like I). This scheme provides 334 letter combinations. After that variable stars are numbered, with the letter V before, e.g. V 404 Cygni.

So, R Coronae Borealis was the first variable star to be discovered in its constellation, and RR Lyrae was the 10th variable found in Lyra.

Places to go for more information:
Most university-level astronomy textbooks will have a lot of information about variable stars (I got the information about the naming business from Abell's "Exploratin of the Universe") as does David Levy's "Observing Variable Stars: A Guide for the Beginner" (1989, Cambridge University Press). Also see two websites The Astronomical Society of South Australia's Variable Star Group and The American Association of Variable Star Observers.

Pauline