Most of his research focused on physics of nebulae, star systems, and extragalactic astronomy. Novae can be used in much the same way as supernovae to derive extragalactic distances. Observation and discovery of extragalactic supernovae are now far more common. See also cosmic neutrino background and extragalactic background light. Type Ia supernovae are some of the best ways to determine extragalactic distances. There are several different methods for which supernovae can be used to measure extragalactic distances. The device allows for near-instantaneous travel across both interstellar and extragalactic distances. Geller is known for observational and theoretical work in cosmology and extragalactic astronomy. This approach forms part of the cosmic distance ladder for measuring distances to extragalactic objects. Astronomers are interested in studying this galaxy as it can help in measuring extragalactic distances. M87 continued to be labelled as an extragalactic nebula at least until 1954. The almanac largely contains solar system ephemeris and catalogs of selected stellar and extragalactic objects. In parallel, the use of interferometric arrays for extragalactic H-I spectroscopy was being developed. One of these extragalactic novae, M31N 2008-12a, erupts as frequently as once every 12 months. This resulted in an accurate but indirect link to an inertial, extragalactic, reference frame.