Spirals
– classified by size of central bulge
•tightness of spiral
pattern correlated with bulge size
•arms more knotty Sa ® Sc
•i/s gas (21 cm (H)
& molecular line radiation) increases Sa
® Sc
•A & G stars in
disk ® whitish color
•new O & B stars
b(+ nebulae) in arms ® bluish color
•Barred spirals – SBa ®
SBc (massive dark
matter halo ® no bar?)