Cistus, with its many hybrids and cultivars, is commonly encountered as a garden flower. The common name rockrose is applied to the species, a name also shared by the related genera Halimium, Helianthemum and Tuberaria, all in the family Cistaceae. The common name gum cistus is applied to resin-bearing species, especially C. ladanifer.
Quasars are part of a class of objects known as active galactic nuclei (AGN). Other classes include Seyfert galaxies and blazars. All three require supermassive black holes to power them.
Optical Telescopes. In optical astronomy there are three basic types of telescopes; the refractor, the catadioptric and the reflector. The refractor telescope receives light through the objective lens (the large lens closest to the subject being viewed) and sends it to the eyepiece for magnification.