NEBULAE & STAR CLUSTERS A  B  C  D  E  F  G  H  I  J  K  L  M  N  O  P  Q  R  S  T  U  V  W  X  Y  Z                    HOME ABOUT CATEGORIES SITE MAP COPYRIGHT ADVERTISE CONTACT entire Web this site OB association 15 × 15 arcminute field at the center of the Cygnus OB2 association. Image: Palomar Sky Survey A loose grouping of between about 10 and several hundred O stars and B stars, scattered across a region up to several hundred light-years across. The members of an OB association are all of roughly the same age (or in subgroups of the same age) and formed from the same interstellar cloud within the past few million years. See also T association. Related category    • NEBULAE AND STAR CLUSTERS Also on this site: Encyclopedia of Alternative Energy & Sustainable Living Encyclopedia of History Transport Concepts & Designs (partner site) BACK TO TOP