Spectroscopic methods were predominantly used by physicists and astrophysicists. It is studied by physicists and astrophysicists. This issue is further obfuscated by the fact that many astronomers are physicists or astrophysicists. The letters are not standards, but are recognized by common agreement among astronomers and astrophysicists. Ambartsumian was one of the leading astrophysicists and astronomers of the 20th century. Radiance is also sometimes called "intensity", especially by astronomers and astrophysicists, and in heat transfer. Some astrophysicists were unconvinced that the cosmological redshifts are caused by universal cosmological expansion. Astrophysicists have applied tidal theories to predict the obliquity of extrasolar planets. By the 1950s, speculating about antimatter comets and meteoroids was a commonplace exercise for astrophysicists. The shapes of these nova nebulae are of much interest to modern astrophysicists. Astrometric measurements are used by astrophysicists to constrain certain models in celestial mechanics. This is helpful for astrophysicists interested in predicting the behavior of supernova remnants. However, some communities of astrophysicists continue to call the muon a "mu-meson". Such a network would afford astrophysicists with more robust search capabilities and higher scientific yields. Astrophysicists classify this as a fourth type of rock&colon; Primitive rock.