Another very good idea, looks really great. But you can use it to show more than just sizes! This is a very good moment to show shapes of stars and their changes too. Giants in general are not perfectly spherical - it's impossible on this scale! Maybe you should try to make a giant as a combination of a few spheres which rotate around its "centre of mass"? Here is a numerical simulation of Betelgeuse's shape:
http://www.aip.de/~mst/pub_files/images ... 0086_E.gif
http://www.aip.de/~mst/pub_files/images ... _I1brm.jpg
There are movies somewhere too, I dont have a link to them - if you want I can send them to you (timescale of changes and their sizes are important).
I think it would be a good idea to add Altair or Achernar due to their elongated shape.
AFAIK Deneb rotates very fast, it should be elongated too.
I mean you shouldnt put all these stars in your extension, but it would be really useful to see stars which differ in sizes AND shapes.
And something about VV Cephei:
"The three stars with the largest known sizes are KW Sagitarii (distance 9,800 light-years), V354 Cephei (distance 9,000 light-years), and KY Cygni (distance 5,200 light-years), all with radii about 1500 times that of the Sun, or about 7 astronomical units(AU). For comparison, the red super-giant star Betelgeuse is known from other work to have a radius about 650 times that of the Sun, or about 3 AU. If one of these stars were placed in the sun?€™s location, its outer layers would extend to midway between the orbits of Jupiter (5.2 AU) and Saturn (9.5 AU). The previous record holder, mu Cephei comes in a close fourth in size in the study. The only other star for which a very large size has been claimed is the binary star system VV Cephei, which consists of a red super-giant and a hot companion orbiting within a common gaseous envelope, in which the gravitational forces of the companion have distended the surface of the super-giant and the meaning of the size of the star is therefore fuzzy. None of the stars in the new study are believed to be binaries, and thus their properties tell us about the extreme sizes that normal stars reach."
Please also check this link (look carefully at Vega and Tsih!):