The stars of the cluster, as seen from Earth, approximate a curving, tapering shape, and it is for this reason that NGC 6633 is occasionally known by another name, the Captain Hook Cluster. The entire cluster spreads across an area of sky approximately equivalent to that of the Moon's disc. None of the individual stars in the cluster exceed eighth magnitude, but the cluster as a whole has a visual magnitude of +4.59 (and so is visible to the naked eye under good seeing conditions).
The brighteststar within the area of the cluster is HD 169959, which lies near the base of the cluster's 'hook' shape. This star is in fact not part of the cluster at all, but a whitegiant lying nearly four times farther from the Solar System, whose light, despite its much greater distance, outshines the foreground stars that truly belong to the Tweedledum Cluster.